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Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023 (2021)

Chapter: 2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items

« Previous: 1 Introduction
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 15
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 16
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 17
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 18
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 19
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 20
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 21
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 22
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 23
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 24
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 25
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Page 26
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 27
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 28
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 29
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 30
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 31
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 32
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 33
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 34
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 35
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 36
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 37
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 38
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 39
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 40
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 41
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 42
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 43
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 44
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 45
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 46
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 47
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 48
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 49
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 50
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 51
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 52
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 53
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 54
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 55
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 56
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 57
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 58
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 59
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 60
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 61
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 62
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 63
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 64
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 65
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 66
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 67
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 68
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
×
Page 69
Suggested Citation:"2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items." National Academies of Sciences, Engineering, and Medicine. 2021. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023. Washington, DC: The National Academies Press. doi: 10.17226/26080.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2 Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Selected WRC-23 and WRC-27 Agenda Items The following pages provide a discussion of the committee’s consensus opinions on the potential impact and relevance of certain agenda items at issue at the upcoming World Radiocommunication Conference (WRC) in 2023 and preliminary agenda items for WRC-27. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 11

AGENDA ITEM 1.2: ALLOCATIONS FOR INTERNATIONAL MOBILE TELECOMMUNICATIONS (IMT) Agenda Item 1.2 considers “identification of the frequency bands 3 300-3 400 MHz, 3 600-3 800 MHz, 6 425-7 025 MHz, 7 025-7 125 MHz and 10.0-10.5 GHz for International Mobile Telecommunications (IMT), including possible additional allocations to the mobile service on a primary basis, in accordance with Resolution 245 (WRC-19).” Resolution 245 (WRC-19) invites the Radiocommunications Sector of the International Telecommunication Union (ITU)-R to conduct and complete in time for WRC-23 sharing and compatibility studies, with a view to ensuring the protection of services to which the frequency band is allocated on a primary basis, without imposing additional regulatory or technical constraints on those services, and also, as appropriate, on services in adjacent bands. Of primary consideration for the science services regarding this agenda item are the frequency bands listed in RR 5.149, RR 5.458, and RR 5.458A. As a general consideration, applicable to all proposed new frequency allocations, care must be taken to assess the impact on incumbent Radio Astronomy Service (RAS) and Earth Exploration-Satellite Service (EESS) bands, including those listed in footnote RR 5.149. While RAS bands can be protected regionally by limiting emissions within a certain radius of a facility, this is not the case with EESS observations, which are typically satellite-based and global in nature. The detrimental interference levels for spectral line RAS observations are approximately −232 dBW/(m2 Hz) at 3300 MHz and −228 dBW/(m2 Hz) at 6650 MHz, respectively, based on interpolation of the values in Table 2 of Recommendation ITU-R RA.769. For EESS (passive), the Recommendation ITU-R RS.2017, interference threshold for these bands is −166 dBW in reference bandwidths of 200 MHz and 100 MHz for 6.425-7.25 GHz and 10.6-10.7 GHz, respectively. Radio Astronomy Service While there are no primary allocations to the RAS in the frequency ranges covered by this agenda item, footnote RR 5.149 urges administrations to take all practicable steps to protect the RAS from harmful interference in a number of bands, including the 3332-3339 MHz, 3345.8-3352.5 MHz, and 6650-6675.2 MHz bands, when making assignments to other services to which the bands are allocated. RR 5.149 states that emissions from spaceborne or airborne stations can be particularly serious sources of interference to the RAS (see Nos. 4.5 and 4.6 and Article 29). In addition, footnote RR 5.458A urges administrations to take all practicable steps to protect spectral-line observations of the RAS in the band 6650-6675.2 MHz from harmful interference from unwanted emissions of space stations of the fixed- satellite service. The frequency ranges 3300-3400 MHz and 6425-7025 MHz overlap three of the lines listed in Recommendation ITU-R RA.314-10 as being among those of greatest importance to radio astronomy. The ranges 3332-3339 MHz and 3345.8-3352.5 MHz are the suggested minimum bands for observation of the 3335 MHz and 3349 MHz lines of the methyladyne (CH) molecule. The band 6650-6675.2 MHz is the minimum suggested band for observation of the 6668 MHz spectral line of the methanol (CH3OH) molecule. The CH molecule, one of the basic building blocks of life, was the first molecule discovered in the interstellar medium. It is found in abundance in star forming regions, such as the Orion Nebula; its observation allows the study of circumstellar shells and the dynamics of star-forming regions in the Milky Way galaxy as well as external galaxies. Observations of the methanol molecule are used to study maser emission in regions that are forming massive stars, their evolution, age and dynamics, as well as in studies of the structure of our galaxy. For example, methanol observations were used to determine that the spiral arms of the Milky Way galaxy extend further than determined previously by other means. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 12

In general, radio observatories are located in remote sites. Signal attenuation at 3.3 and 6.7 GHz is relatively small, and most of the attenuation is due to the inverse square law. Radio astronomy observatories are also vulnerable to out-of-band emission (OOBE) of mobile devices. Full consideration of the impact of new allocations must include the possibility of OOBE and the aggregate emissions from numerous devices. Detailed consideration of RFI to RAS sites must also include analysis appropriate to the geographic location of the observatory. In the United States, observatories that operate in frequency ranges considered include the Very Large Array (New Mexico), the Green Bank Telescope (West Virginia), the Arecibo Observatory (Puerto Rico), 1 the Haystack Observatory (Massachusetts), Owens Valley (California), the Allen Telescope Array (California), and the 10 sites included in the Very Long Baseline Array. Internationally, they include the Parkes telescope and the Australia Telescope Compact Array in Australia; the African VLBI Network telescope in Ghana and the Meerkat telescope (a pathfinder for the future Square Kilometre Array) in South Africa; the 100-m Radio Telescope in Effelsberg, Germany; the 32-m Torun telescope in Poland, the 10 stations of the European VLBI Network (EVN), including Medicina, Noto, and Sardinia in Italy, and Yebes in Spain; the planned Qitai Radio Telescope in China; and the RATAN-600 telescope in Russia. This list of observatories that operate in the 3.3 GHz and 6.6 GHz ranges is intended to be illustrative of the wide use of these frequencies by the RAS, it is not intended to be comprehensive. Earth Exploration-Satellite Service The radio regulations include direct reference to several of the bands under consideration in this agenda item. RR 5.458 states the following: In the band 6425-7075 MHz, passive microwave sensor measurements are carried out over the oceans. In the band 7075-7250 MHz, passive microwave sensor measurements are carried out. Administrations should bear in mind the needs of the Earth exploration-satellite (passive) and space research (passive) services in their future planning of the bands 6425-7075 MHz and 7075-7250 MHz. Further, of relevance to considerations of the 10.0-10.5 GHz band, the nearby 10.6-10.68 GHz region is allocated to EESS (passive) on a co-primary basis, as is the adjacent 10.68-10.7 GHz band that is afforded RR 5.340 “all emissions prohibited” protection. These EESS bands are used to measure a wide range of ocean and land surface properties that are of critical importance in weather prediction, hydrology, etc. For ocean regions, these variables include sea- surface temperature (for which 6.8 GHz conveys the best information available in the 6-15 GHz range), ocean wind speed (and direction for polarimetric microwave radiometers), and sea-ice thickness. Soil moisture is routinely observed in these bands, and their signals are also used in studies of snow depth and snow water equivalent. Table 2.1 provides details of various passive sensors in these bands. In addition to spaceborne sensors, NOAA “Hurricane Hunter” aircraft routinely make passive observations in these bands to provide critical information for hurricane forecasting. While there is generally less conflict between active services and EESS (passive) over the oceans than over land, Earth Stations in Motion (ESIMs) deployed on merchant vessels have the strong potential to create radio frequency interference (RFI) in ocean scenes. In addition, communication systems deployed on smaller islands will also be sources of RFI for these environmental satellite sensors. Since the passive microwave emissions from the sea surface are relatively weak (as is the case for land surface), oceanographers are forced to average over both space and time to get a useful and accurate retrieval. RFI greatly degrades the space-time resolutions of passive microwave systems and would be expected to do so 1 While the former 305-m telescope at Arecibo Observatory is no longer functional, a 12-m radio telescope is operational at the site, and the observatory remains open. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 13

most significantly in the vicinity of shipping lanes and islands—the very places where societal need for accurate and timely measurements are most critical. The 10-10.5 GHz region is overlapped significantly by a 9.9-10.4 GHz co-primary allocation to EESS (active) that can be used for land imaging, such as topographic and surface deformation mapping, surface water and wetlands dynamics, snow extent, coastal zones, and land-cover/land-use change. This recent allocation for synthetic aperture radar, nearly adjacent to a previous 9.3-9.8 GHz co-primary EESS (active) allocation, was made to enable higher spatial resolution imaging. TABLE 2.1 Passive EESS Sensors in the Frequency Bands 6425-7025 MHz, 7025-7125 MHz, and 10.0- 10.5 GHz Center Frequency Bandwidth IFOVb Sensor Satellite (GHz), polarizationa (MHz) (km) AMSR2 JAXA GCOM-W 6.925 V,H 350 36 × 62 AMSR2 JAXA GCOM-W 7.3 V,H 350 35 × 62 AMSR2 JAXA GCOM-W 10.65 V,H 100 24 × 42 WindSat DoD Coriolis 6.8 V,H 125 39 × 71 WindSat DoD Coriolis 10.7 V,H,3,4 300 25 × 38 GMI NASA GPM Core 10.65 V,H 100 19 × 32 MTVZA-GY-MP RosHydroMet Meteor-MP N1/N2 6.9 V,H 400 135 × 302 MTVZA-GY-MP RosHydroMet Meteor-MP N1/N2 10.6 V,H 100 89 × 198 MTVZA-GY RosHydroMet Meteor-M N2-1/5 10.6 V,H 100 89 × 108 MWRI NSOAS HY-2A/B 6.6 V,H 350 80 × 120 MWRI NSOAS HY-2A/B 10.7 V,H 250 50 × 75 MWRI CMA FY3A-H 10.65 V,H 180 51 × 85 CIMR Copernicus 6.925 V,H,3,4 825 max. <15 km CIMR Copernicus 10.65 V,H,3,4 100 < 15 km MWI DoD WSF-M 10.85 V,H,3,4 500 23 × 38 AMSR3 JAXA GOSAT-GW 6.925 V,H 350 36 × 62 AMSR3 JAXA GOSAT-GW 7.3 V,H 350 35 × 62 AMSR3 JAXA GOSAT-GW 10.65 V,H 100 24 × 42 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Polarization codes are H-horizontal, V-vertical, 3 and 4—3rd and 4th elements of the Stokes vector. b Instantaneous field-of-view dimensions. Recommendation: The committee recommends that if the 3300-3400 MHz, the 6425-7025 MHz, and/or the 7025-7125 MHz frequency bands are identified for International Mobile Telecommunications (IMT), the strongest possible protections be provided to the RAS for observations of the two CH lines in the 3332-3339 MHz and 3345.8-3352.5 MHz bands and to the methanol line in the 6650-6675.2 MHz band, all of which are included in RR 5.149. Similarly, strong protection should be provided to the EESS in the bands 6425-7075 and 7075-7250 MHz, in which essential observations are carried out over the oceans, and that are included in RR 5.458. The committee believes that the most effective protection would be through a primary allocation to the RAS and EESS in the relatively small bands of interest to these services, should a primary allocation to mobile services be made in the broader frequency bands. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 14

Alternatively, the bands of interest to the RAS could be protected by appropriate exclusion zones set up by national or, if needed, multinational agreements. Account should be taken of aeronautical uses, if and when applicable. In addition to an exclusion zone around each RAS facility, likely growth of the IMT service and the impact of future aggregate interference must be taken into account in all sharing and compatibility studies. If identifications are made to the IMT in these frequency ranges, under this alternative, an international footnote that calls attention to the necessity of protecting the RAS and EESS in the bands affected should also be adopted. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 15

AGENDA ITEM 1.4: HIGH-ALTITUDE PLATFORM STATIONS AS IMT BASE STATIONS Agenda Item 1.4 calls to consider “in accordance with Resolution 247 (WRC-19), the use of high- altitude platform stations as IMT base stations (HIBS) in the mobile service in certain frequency bands below 2.7 GHz already identified for IMT, on a global or regional level.” Resolution 247 (WRC-19) recognizes “that the frequency bands 1885-1980 MHz, 2010-2025 MHz, and 2110-2170 MHz in Regions 1 and 3 and the frequency bands 1885-1980 MHz and 2110-2160 MHz in Region 2 are included in No. 5.388A for the use of HIBS, in accordance with the provisions of Resolution 221 (Rev. WRC-07).” Further, Resolution 247 (WRC-19) resolves to invite sharing and compatibility studies to be completed in time for WRC-23 for high-altitude platform stations, to be used as IMT base stations, “to ensure protection of services … to which the frequency band is allocated on a primary basis … and the planned development of primary allocated services, and adjacent services, as appropriate, for certain frequency bands below 2.7 GHz, or portions thereof, globally or regionally harmonized for IMT.” The frequency bands include the following: “694-960 MHz; 1710-1885 MHz (1710-1815 MHz to be used for uplink only in Region 3); 2500-2690 MHz (2500-2535 MHz to be used for uplink only in Region 3, except 2655-2690 MHz in Region 3).” It is important to note that while Resolution 247 (WRC-19) recognizes “d) that some frequency bands below 2.7 GHz are globally or regionally identified for IMT in accordance with Nos. 5.286AA, 5.317A, 5.341A, 5.341B, 5.341C, 5.346, 5.346A, 5.384A, and 5.388,” the Resolution specifically states “that changes to the footnotes referred to in recognizing d) are outside the scope and there should be no additional regulatory or technical constraints imposed on the deployment of ground-based IMT systems in the frequency bands referred to in those footnotes.” The footnotes in recognizing d) (listed above) include the following frequency bands: 450-470 MHz; 698-960 MHz (Region 2) and 694-790 MHz (Region 1) and 790-960 (Regions 1 and 3); 1427-1452 MHz and 1492-1518 MHz (Region 1); 1427-1518 MHz (Region 2); 1427-1452 MHz and 1492-1518 MHz (Region 3); 1452-1492 MHz (many countries in Region 1); 1452-1492 MHz (Region 3); 1710-1885 MHz, 2300-2400 MHz, and 2500-2690 MHz; and 1885-2025 and 2110-2200 MHz. Thus, for this agenda item, the primary concern for the scientific services is the adjacent 2690-2700 MHz band allocated to EESS (passive), RAS, and Space Research (passive) worldwide and the secondary allocation to radio astronomy at 1718.8-1722.2 MHz (RR 5.385). The 2690-2700 MHz band is included in RR 5.340, among those in which “all emissions are prohibited” except in the case of the countries listed in RR 5.422 that include a co-allocation for fixed and mobile, except aeronautical mobile, services on a primary basis, with use limited to equipment in operation by 1 January 1985. In addition, secondary harmonics from portions of the 694-960 MHz band place the following L band science services bands at risk: 1400-1427 MHz, 1610.3-1613.8 MHz, 1660-1670 MHz, and 1718.6-1722.2 MHz. The frequency band 1400-1427 MHz is allocated to EESS (passive), RAS, and Space Research (passive) worldwide and is included in RR 5.340, where “all emissions are prohibited.” The 1610.3-1613.8 MHz and 1660-1670 MHz bands are allocated to RAS on a primary basis and, along with the 1718.6-1722.2 MHz band, are listed in RR 5.149, where administrations are urged to take all practicable steps to protect radio astronomy. As listed in Recommendation ITU-R RA.769, the threshold level for detrimental interference to RAS at 2695 MHz is −247 dBW/(m2 Hz), For spectral line observations in the frequency bands that are at risk from harmonics of the 694-960 MHz band, the threshold levels for detrimental interference to RAS are −239 dBW/(m2 Hz), −238 dBW/(m2 Hz), and −237 dBW/(m2 Hz), at 1.42 GHz, 1.61 GHz, and 1.66 GHz, respectively. Recommendation ITU-R RS.2017 lists a maximum interference level of −176 dBW in a 10 MHz bandwidth within the frequency band of 2.64-2.70 GHz for EESS sensors. For the frequency bands that are at risk from harmonics of the 694-960 MHz band, the maximum interference level for EESS sensors from HIBS base stations is −182 dBW in 27 MHz for the 1.370-1.427 GHz band (ITU-R RS.2336). PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 16

Radio Astronomy Service Emissions from spaceborne and airborne stations, including high-altitude platform stations, can be particularly serious sources of interference to the RAS. The adjacent 2690-2700 MHz band is used by the RAS for studies of the ionized gas in the Milky Way galaxy and the general diffuse galactic background. It is also one of the most useful frequency bands for polarization studies, that allow studies of magnetic fields in our own and external galaxies. Care should be taken that out-of-band emission (OOBE) levels conform to the listed detrimental power levels in Recommendation ITU-R RA.769, −247 dBW/(m2 Hz) at 2695 MHz, even with the establishment of maximum allowed power levels in the neighboring frequency range. In addition, unwanted emission from harmonics of the 694-960 MHz band may lead to radio frequency interference into the 1400-1427 MHz band, designed for observation of neutral hydrogen in our own and nearby galaxies (which is protected by RR 5.340) and into other frequency bands where RAS is co-primary, including frequency bands designed for observations of the OH emission line (1610.6-1613.8 MHz and 1660-1670 MHz, both of which are listed in RR 5.149, where administrations are urged to take all practicable steps to protect the radio astronomy service). Observations of the neutral hydrogen emission line and OH emission lines are essential for our understanding of the nature of the universe and of star formation processes. Any deployment of HIBS should consider their impact and line of sight toward radio astronomy telescopes observing in the intended transmission bands. This includes transmissions between HIBS platforms, as well as the ground-to-HIBS and HIBS-to-ground transmissions, and the full beam patterns and elevation ranges of the radio telescopes. Several major RAS facilities in the United States operate in or near these frequency bands, including the Robert C. Byrd Green Bank Telescope (GBT), the Karl G. Jansky Very Large Array (VLA), the Very Long Baseline Array (an instrument with 10 discrete receiving stations spread over North America), and the Arecibo Observatory. 2 Globally, facilities include the MeerKAT telescope in South Africa, the Australian SKA Pathfinder and Parkes 64-m in Australia, the Effelsberg radio telescope in Germany, the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in China and future facilities such as the Square Kilometre Array (SKA) and next generation Very Large Array (ngVLA). Earth Exploration-Satellite Service HIBS use of 2500-2690 MHz is potentially quite problematic, as 2655-2690 MHz is an EESS passive secondary band. Although there are no currently operating missions, this band is immediately adjacent to 2690-2700 MHz, which is protected as an EESS (passive) primary allocation by RR 5.340 (except per RR 5.422 as noted above). Furthermore, the critically important U.S. operational weather radar network (WSR-88D/NEXRAD) operates at 2700-3000 MHz. HIBS proposed use of 2500-2690 MHz may pose adjacent interference concerns if the 2690-2700 MHz guard band (effectively implemented by EESS (passive) through RR 5.340) is not adequate to prevent overwhelming the NEXRAD radar receiver’s front end interference rejection filters. There are more than 160 NEXRAD systems that run around the clock to support the weather warning and forecast missions of the National Weather Service, the Federal Aviation Administration (FAA), and DoD, along with supporting fundamental meteorology research. NEXRAD data are vital to life safety, and its weather information products have very significant societal and economic impact through storm forecast, property damage avoidance, and related services. Of additional concern, harmonics from HIBS 694-960 MHz transmissions may result in radio frequency interference in other EESS bands. For example, the 1400-1427 MHz band is protected and heavily used for EESS based soil moisture, sea-surface salinity, and vegetation biomass observations as extensively documented in ITU-R RS.2336. In addition to harmonics from the proposed HIBS bands, 2 While the former 305-m telescope at Arecibo Observatory is no longer functional, a 12-m radio telescope is operational at the site and the observatory remains open. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 17

1400-1427 MHz is adjacent to the 1427-1452 MHz IMT band referenced in RR 5.341A, 5.341B, and 5.341C, where HIBS out-of-band emission levels must remain below −182 dBW/27 MHz (base station assumed) to avoid interference according to ITU RS.2336. Recommendation: The committee recommends that if High-altitude platform stations as IMT Base Stations (HIBS) are authorized to operate in the frequency bands listed in Resolution 247 (WRC-19) (i.e., 694-960 MHz, 1710-1885 MHz, and 2500-2690 MHz), then radio astronomy bands must be protected from both in-band and harmonic unwanted emissions of HIBS by at least the power density levels listed in Recommendation ITU-R RA.769. For EESS band protections, the committee recommends protection from unwanted harmonics of 694-960 MHz HIBS emissions to at least the maximum power density levels listed in ITU-R RS.2336, and consideration of appropriate sharing and compatibility studies for the 2655-2690 MHz frequency band, including potential HIBS impact on NEXRAD system performance at 2700-3000 MHz. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 18

AGENDA ITEM 1.5: SPECTRUM USE IN THE FREQUENCY BAND 470 – 694 MHz IN REGION 1 Agenda Item 1.5 is “to review the spectrum use and spectrum needs of existing services in the frequency band 470-960 MHz in Region 1 and consider possible regulatory actions in the frequency band 470-694 MHz on the basis of the review in accordance with Resolution 235 (WRC-15). Resolution 235 (WRC-15) considers “that it is necessary to adequately protect all primary services in the frequency band 470-694 MHz and in adjacent frequency bands”; furthermore, it states “that, in some countries, parts of the frequency band are also allocated to the radiolocation service on a secondary basis, limited to the operation of wind profiler radars (No. 5.291A), and also to the radio astronomy service on a secondary basis (No. 5.306), and, according to No. 5.149, administrations are urged to take all practicable steps to protect the radio astronomy service from harmful interference when making assignments to stations of other services.” Recommendation ITU-R RA.769 states that radio astronomy protection in 606-614 MHz requires interference levels to remain below −253 dBW/(m2 Hz) for continuum radio astronomy and below −211 dBW/(m2 Hz) for very long baseline interferometry applications. Radio Astronomy Service In Region 1, there is an additional allocation of 606-614 MHz to radio astronomy on a primary basis in the African Broadcast Area (RR 5.304) and an allocation of 608-614 MHz to radio astronomy on a secondary basis in other areas of Region 1 (RR 5.306). This frequency range is particularly crucial for the study of pulsars, rapidly rotating neutron stars, and elusive fast radio bursts, and is crucial for the study of baryon acoustic oscillations, which probe the matter distribution in the universe via measurement of redshifted 21-cm line emission (arising from the spin flip of neutral hydrogen, the most abundant atom in the universe, with a rest frequency at 1420.4058 MHz). All of these scientific studies require a wide bandwidth to detect faint cosmic emissions at sufficient signal-to-noise ratio. Many radio telescopes have receivers that operate at these frequencies. Protection of this frequency band for radio astronomy in Region 1 is of interest to astronomers worldwide, as the band is often used for Very Long Baseline Interferometry observations that involve radio telescopes on different continents. For example, the Very Long Baseline Array, situated across North America, has receivers operating in the relevant frequency range and is frequently joined by other international facilities, especially from Region 1, for joint observing campaigns. Local interference isolated to Region 1 can have adverse effects on such observations. The committee notes that several major RAS facilities operate in this frequency range in Region 1, which includes the MeerKAT radio telescope in South Africa, the radio telescope in Effelsberg, Germany, and the Observation Radiospéctrale pour FEDOME et les Etudes des Eruptions Solaires (ORFEES) spectrograph at Nançay in France, the Lovell telescope in United Kingdom, and RATAN-600 in Zelenchukskaya, Russia. Future facilities covering this frequency range will include the international Square Kilometre Array (SKA) and the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) in South Africa, which also includes collaboration from U.S. institutions such as the National Radio Astronomy Observatory, NASA’s Jet Propulsion Laboratory, Caltech, Yale University, Carnegie Mellon University, University of Wisconsin, and West Virginia University. The geographic location of MeerKAT and the future SKA has additional protection through South Africa’s Astronomy Geographic Advantage Act (2007). PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 19

Earth Remote Sensing Application of the Radiolocation Service: Wind-Profiling Radar The frequency band 470-494 MHz is currently allocated to radiolocation services as secondary service for wind profiling in several European countries (RR 5.291A). Resolution 217 (WRC-97) identifies wind-profiler radars as “important meteorological systems used to measure wind direction and speed as a function of altitude.” These vertical Doppler radar systems, known at UHF frequencies as boundary layer radars, provide unique capabilities for measuring and monitoring wind velocities in clear air with high height and time resolutions from the ground to several kilometers in altitude. Wind profiler data are also essential to crucial whole-atmosphere research into gravity waves, turbulence, temperature and humidity profiling, precipitation systems, and stratosphere-troposphere exchange processes. These topics fundamentally inform knowledge on lower atmosphere structure along with energy and momentum exchange. Several national and international wind profiler networks (e.g., Co-Ordinated Wind Profiler Network in Europe) provide upper-air wind data to numerical weather prediction. UHF frequencies are ideal for boundary layer radars due to the physical scales of turbulent eddies. Recommendation: Any changes regarding the use of the radio spectrum between 470-960 MHz should include the study and careful consideration of the impact on the 608-614 MHz radio astronomy band (606-614 MHz in the African Broadcast Area). Continued RAS use of the 608-614 MHz band in Region 1 (606-614 MHz in the African Broadcast Area) must be safeguarded. To protect atmospheric sounding, the committee recommends further study and careful consideration of changes in use, for at least 470-494 MHz, to minimize impacts on UHF wind-profiler systems. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 20

AGENDA ITEM 1.8: USE OF FIXED SATELLITE SERVICE NETWORKS BY CONTROL AND NON-PAYLOAD COMMUNICATIONS OF UNMANNED AIRCRAFT SYSTEMS Agenda Item 1.8 considers “on the basis of ITU-R studies in accordance with Resolution 171 (WRC- 19), appropriate regulatory actions, with a view to reviewing and, if necessary, revising Resolution 155 (Rev.WRC-19) and No. 5.484B to accommodate the use of fixed-satellite service (FSS) networks by control and non-payload communications of unmanned aircraft systems.” Resolution 171 (WRC-19) in turn resolves to review and possibly revise Resolution 155 (Rev.WRC-19) and RR 5.484B in the frequency bands to which they apply. RR 5.484B states that Resolution 155 shall apply. Resolves 1 of Resolution 155, as revised by WRC-19, states “that assignments to stations of [geostationary] FSS networks operating in the frequency bands 10.95-11.2 GHz (space-to- Earth), 11.45-11.7 GHz (space-to-Earth), 11.7-12.2 GHz (space-to-Earth) in Region 2, 12.2-12.5 GHz (space-to-Earth) in Region 3, 12.5-12.75 GHz (space-to-Earth) in Regions 1 and 3 and 19.7-20.2 GHz (space-to-Earth), and in the frequency bands 14-14.47 GHz (Earth-to-space) and 29.5-30.0 GHz (Earth- to-space), may be used for [Unmanned Aircraft Systems] (UAS) [Control and Non-Payload Communications] (CNPC) links in non-segregated airspace, * provided that the conditions specified in resolves below are met.” Resolves 17 of Resolution 155 refers to the RAS. It states that “in order to protect the radio astronomy service in the frequency band 14.47-14.5 GHz, administrations operating UAS in accordance with this Resolution in the frequency band 14-14.47 GHz within line-of-sight of radio astronomy stations are urged to take all practicable steps to ensure that the emissions from the UA in the frequency band 14.47-14.5 GHz do not exceed the levels and percentage of data loss given in the most recent versions of Recommendations ITU-R RA.769 and ITU-R RA.1513.” Additionally, RR 5.504B states that “Aircraft earth stations operating in the aeronautical mobile- satellite service in the band 14-14.5 GHz shall comply with the provisions of Annex 1, Part C of Recommendation ITU-R M.1643, with respect to any radio astronomy station performing observations in the 14.47-14.5 GHz band located on the territory of Spain, France, India, Italy, the United Kingdom and South Africa.” In the United States, footnote US133 applies. With respect to the 14.47-14.5 GHz band, the footnote states the following provision shall apply to the operations of Earth Stations Aboard Aircraft (ESAA): “In the band 14.47-14.5 GHz, operations within radio line-of-sight of the radio astronomy stations specified in 47 CFR 25.226(d)(2) are subject to coordination with the National Science Foundation in accordance with 47 CFR 25.227(d).” In the United States, a formal notification procedure has been established through the National Radio Astronomy Observatory (NRAO) to advise ESAA operators when radio astronomy observations are conducted in the band. Of primary consideration for the science services is the adjacent frequency band 14.47-14.5 GHz listed in RR 5.149 and allocated on a secondary basis worldwide. RR 5.149 urges administration to take all practicable steps to protect the RAS from harmful interference in a number of bands, including the 14.47-14.5 GHz band, when making assignments to other services to which the bands are allocated. RR 5.149 states that emissions from spaceborne or airborne stations can be particularly serious sources of interference to the RAS (see Nos. 4.5 and 4.6 and Article 29). As noted in Recommendation ITU-R RA.769, the threshold level considered detrimental to radio astronomy spectral line observations in this frequency band is −221 dBW/(m2 Hz). * May also be used consistent with international standards and practices approved by the responsible civil aviation authority. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 21

Radio Astronomy Service The 14.47-14.5 GHz band is used for observations of the 14.488 GHz formaldehyde line in the Milky Way galaxy. This line is included in the list of lines of greatest importance to radio astronomy in Recommendation ITU-R RA.314-10. In the United States, observations in this band are conducted at, for example, the Green Bank Telescope, the Very Large Array (VLA), and the 10 stations of the Very Long Baseline Array. Observations in the band are carried out worldwide; for example, at Jodrell Bank, U.K., Effelsberg, Germany, Parkes, Australia, and a number of other locations in Asia, Africa, Australia, and Europe. Recommendation: The committee recommends that, with respect to radio astronomy stations performing observations in the 14.47-14.5 GHz band, protections from in-band and unwanted emissions from Control and Non-Payload Communications from Unmanned Aircraft Systems that are similar to those of the provisions of Annex 1, Part C, of Recommendation ITU-R M.1643, should be adopted worldwide. The committee recommends the adoption of a footnote to the Radio Regulations that specifies such protections. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 22

AGENDA ITEM 1.9: REVIEW APPENDIX 27 (2.850-22.000 MHz) OF THE RADIO REGULATIONS TO ACCOMMODATE DIGITAL TECHNOLOGIES Agenda Item 1.9 requests “review Appendix 27 of the Radio Regulations and consider appropriate regulatory actions and updates based on ITU-R studies, in order to accommodate digital technologies for commercial aviation safety-of-life applications in existing HF bands allocated to the aeronautical mobile (route) service and ensure coexistence of current HF systems alongside modernized HF systems, in accordance with Resolution 429 (WRC-19)” The frequency bands under consideration of Resolution 429 (WRC-19) are as follows: 2.850-3.025, 3.400-3.500, 4.650-4.700, 5.450-5.680, 6.525-6.685, 8.815-8.965, 10.005-10.1, 11.275-11.400, 13.260- 13.360, 17.900-17.970, and 21.924-22.000 MHz. Of concern to the science services is the adjacent RAS allocation at 13.36-13.41 MHz. To avoid interference with the RAS, out-of-band emission (OOBE) levels should conform to the detrimental power levels in Recommendation ITU-R RA.769, which is −248 dBW/(m2 Hz) at 13.385 MHz. Radio Astronomy Service Emissions from aeronautical stations can be particularly serious sources of interference to radio astronomy due to increased propagation of signals at high altitudes. Furthermore, emissions at frequencies close to the ionospheric cut-off have the ability to reflect off the ionosphere and ground and can potentially be detected around the entire globe. For RAS, the primary concern for this agenda item is the primary RAS band at 13.36-13.41 MHz, which is adjacent to the 13.260-13.360 MHz band, one of the frequency allocations under review. Care should be taken according to Resolution 429 (WRC-19) that “any channel aggregation needs to be performed in a manner that protects other primary services operating in band and in adjacent frequency bands.” This could be achieved by avoidance of digital broadcasting at the edge of the RAS allocation and institution of a guard band. The RAS allocation at 13.36-13.41 MHz is particularly important for the study and monitoring of solar activity, Jovian radio emission, radio emission of meteor trails, and passive ionospheric research, including lightning, as well as steep-spectrum radio sources like pulsars, rapidly spinning neutron stars. Several RAS facilities in the United States operate in or near these frequency bands, including stations of the Long Wavelength Array in New Mexico and at Owens Valley Radio Observatory in California, as well as the Low Frequency All Sky Monitor (LoFASM) with deployments distributed across the United States and the U.S. Naval Research Laboratory’s Deployable Low Frequency Ionosphere and Transient Experiment (DLITE), which currently has deployments in New Mexico and Maryland. Furthermore, many smaller deployments through NASA’s Radio JOVE project allow amateur scientists and students to observe and analyze decametric radio emission from Jupiter and the sun in this frequency range. Globally, facilities include, among others, the Low Frequency Array (LOFAR) with central stations in the Netherlands and outlying stations in several other European countries, the Giant Ukrainian Radio Telescope, the Ukrainian T-shaped Radio telescope, NenuFAR (France), and the Nançay Decameter Array (France). Recommendation: The committee recommends that any new allocations to digital technologies focus on frequency allocations below 13.0 MHz listed in Appendix 27, where radio astronomy observations are difficult by the nature of the ionosphere. Furthermore, in order to protect the RAS primary allocation from out-of-band emissions, the committee recommends avoiding allocations to airborne systems adjacent to primary RAS bands, such as the 13.260-13.360 MHz band listed in Appendix 27, which is adjacent to the primary RAS band at 13.36-13.41 MHz. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 23

AGENDA ITEM 1.10: ALLOCATIONS TO THE AERONAUTICAL MOBILE SERVICE Agenda Item 1.10 proposes “to conduct studies on spectrum needs, coexistence with radiocommunication services and regulatory measures for possible new allocations for the aeronautical mobile service for the use of non-safety aeronautical mobile applications, in accordance with Resolution 430 (WRC-19).” Resolution 430 (WRC-19) invites sharing and compatibility studies in the frequency bands 15.4-15.7 GHz and 22-22.21 GHz and the definition of appropriate protection levels for unwanted emissions into the adjacent bands allocated to the passive services. Of particular concern for the science services are the potential for increased transmissions at 22-22.21 GHz, where administrations are urged to take all practicable steps to protect the RAS (RR 5.149). In addition, out-of-band emissions into adjacent allocations for RAS and EESS at 15.35-15.4 GHz, which is protected by RR 5.340, and 22.21-22.5 GHz, which is allocated to EESS and RAS and protected by RR 5.149, are of concern for this agenda item. While Resolution 430 (WRC-19) invites “definition of appropriate protection for the passive services and the RAS allocation in adjacent frequency bands from unwanted emissions of the [Aeronautical Mobile Service] (AMS),” it is important to note that threshold levels for the EESS and RAS are identified in Recommendations ITU-R RS.2017 and ITU-R RA.769, respectively. Indeed, as noted in Recommendation ITU-R RA.769, the appropriate protection levels for radio astronomy are −233 dBW/(m2 Hz) for continuum observations at 15.375 GHz and −216 dBW/(m2 Hz) for spectral line observations at 22.2 GHz. As noted in Recommendation ITU-R RS.2017, the appropriate protection levels for EESS at 15.2-15.4 GHz is −169 dBW in a 50 MHz bandwidth and at 22.21-22.5 GHz it is −169 dBW in a 200 MHz bandwidth. Sharing and compatibility studies should consider aggregate interference from multiple transmitting sources that could affect the protected passive EESS sensors and radio astronomy telescopes. As a general rule, airborne emissions are particularly problematic for both radio astronomy and Earth remote sensing applications. Radio Astronomy Service The 15.35-15.4 GHz band is included in RR 5.340. This regulation states that all emissions are prohibited in the band, except in a handful of countries, listed in RR 5.511, where this band is also allocated to the fixed and mobile services on a secondary basis. RR 5.511F provides protection of the band from out-of-band emissions of the radiolocation stations operating in the frequency band 15.4-15.7 GHz, stating that those emissions “shall not exceed the power flux-density level of −156 dB(W/m2) in a 50 MHz bandwidth in the frequency band 15.35-15.4 GHz, at any radio astronomy observatory site for more than 2 percent of the time.” The 22.0-22.21 GHz band is allocated to the fixed and mobile, except aeronautical mobile, services on a primary basis, while the 22.21-22.5 GHz band is shared by the passive services with the fixed and mobile, except aeronautical mobile, services. Both bands are included in RR 5.149, which urges administrations to take all practicable steps to protect the RAS from harmful interference and notes that emissions from spaceborne or airborne stations can be particularly serious sources of interference to the RAS. These bands include the recommended frequency allocation for the 22.235 GHz water (H2O) line, as listed in Recommendation ITU-R RA.314-10. This water line is a critical tracer of the dynamical motions in the envelopes of forming stars and the accretion disks surrounding supermassive black holes in the centers of galaxies. The 15.35-15.40 GHz band, adjacent to the 15.4-15.7 GHz band proposed for study in AI 1.10, is used for a range of both radio continuum and line observations. Radio continuum observations, which require large bandwidth regions that are relatively unpolluted by radio frequency interference, are essential in the Ku band (12-18 GHz) and K band (18-27 GHz) for measuring free-free (Bremsstrahlung) PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 24

radiation generated in ionized gas. Measurements of continuum emission at these frequency bands are the least contaminated by dust emission (which peaks at higher frequencies) and synchrotron emission (which peaks at lower frequencies). In essence, continuum observations in these bands are effectively the only way to cleanly observe ionized gas that is optically obscured. This ability is essential for probing areas of star formation throughout the Milky Way and the universe. A number of important molecules also have transitions in frequency bands affected by this agenda item. These include ammonia, formaldehyde, methanol, and radio recombination lines (of both hydrogen and carbon). Ammonia was in fact the first polyatomic molecule detected in space. It has transitions that are commonly used to trace kinematics and measure temperatures in the interstellar medium and star- forming regions. These measurements require observing a number of transitions. Radio recombination lines (RRLs), including those of both hydrogen and carbon, are the only way of measuring ionization in interstellar space directly. With a set of RRLs across a range of frequencies, it is also possible to determine the density of the medium from which they are emitted. Of particular concern for this agenda item are the ammonia line at 15.391 GHz, the carbon recombination line at 15.351 GHz, and the hydrogen recombination line at 15.360 GHz, which are included in the RAS allocation adjacent to the frequencies considered in this agenda item. The wealth of information derived from observations of these and other spectral lines provide insight into the formation, structure, and physical properties of molecular clouds in both the Milky Way and nearby galaxies. Radio telescopes that operate at these frequencies include, among others, HartRAO (South Africa), Nanshan (China), Tian Ma (China), Nobeyama Radio Observatory (Japan), VERA (Japan), Badary Radio Astronomical Observatory (Russia), Australia Telescope Compact Array (Australia), Mopra Radio Telescope (Australia), Parkes Observatory (Australia), Mount Pleasant Radio Telescope (Tasmania), Radioastronomical Observatory (Russia), Svetloe Radio Astronomical Observatory (Russia), VLBI (Italy), MERLIN (England), Metsähovi Radio Observatory (Finland), Onsala Space Observatory (Sweden), São Gião Radio Telescope (Portugal), Very Large Array (USA), Green Bank Telescope (USA), and the 10 stations of the Very Long Baseline Array (USA). As noted in RR 5.149, “emissions from spaceborne or airborne stations can be particularly serious sources of interference to the radio astronomy service.” Earth Exploration-Satellite Service The 22 GHz region is highly valuable for operational meteorological applications and research because it encompasses a strong water vapor spectral line at 22.235 GHz. EESS (passive) observations in this spectral band provide unique information on atmospheric water vapor and relative humidity, properties that are central to weather and particularly to the forecasting of extreme weather. Table 2.2 lists the sensors measuring in this band that are used for meteorological applications and research. These include the DMSP F15, F16, F17, and F18 satellites carrying a 22.23 GHz channel on the SSMI/SSMIS sensors operating in a conical scanning mode. Note that the 15.35-15.4 GHz band, although allocated to EESS (passive) as discussed above, is not observed by any current EESS (passive) sensor. It is important to note that while ground-to-ground transmissions in the 22-22.21 GHz band (and the adjacent shared band at 22.21-22.5 GHz) are currently permitted, the direct beam of a near-horizontal ground-to-ground link in this frequency range experiences strong atmospheric absorption and is thus significantly attenuated before reaching an orbiting EESS (passive) sensor. However, transmissions, including out-of-band emissions, from potential future emitters onboard commercial or other aircraft will experience far less atmospheric attenuation before being received by a spaceborne EESS sensor. In addition, the aggregate interference from numerous aircraft within the footprint of an EESS sensor raises further concerns. Thus, the current restriction “except aeronautical mobile” is well justified in these frequency bands. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 25

TABLE 2.2 Passive EESS Sensors Measuring in Frequency Bands Close to 22-22.21 GHz Center Frequency (GHz) and Bandwidth IFOVb Sensor Satellite polarizationa (MHz) (km) SSM/I DMSP-F15 22.235 V 400 40 × 60 SSMIS DMSP-F16, F17, and F18 22.235 V 407 42.4 × 70.1 NOTE: Acronyms are defined in Appendix B. a V indicates vertical polarization. b Instantaneous field-of-view dimensions. Recommendation: The committee recommends that the protection levels in Recommendations ITU- R RA.769 and ITU-R RS.2017 be adopted for sharing and compatibility studies associated with Agenda Item 1.10, as no further definition of the appropriate protection levels from unwanted emissions into the adjacent passive services bands is necessary. Further, if additional allocations are considered at 22.0-22.21 GHz, a primary allocation for RAS and EESS (passive) in the 22.0-22.21 GHz band should be considered to provide additional protection of the passive services in this frequency band, particularly since airborne and spaceborne emissions can be serious sources of interference for RAS (RR 5.149). PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 26

AGENDA ITEM 1.11: MODERNIZING THE GLOBAL MARITIME DISTRESS SYSTEM Agenda Item 1.11 considers “possible regulatory actions to support the modernization of the Global Maritime Distress and Safety System and the implementation of e-navigation, in accordance with Resolution 361 (Rev.WRC-19).” Resolution 361 (Rev. WRC-19) recognizes that the International Maritime Organization (IMO) is “evaluating an application to recognize the existing geostationary-satellite system operation on 1610- 1626.5 MHz (Earth-to-space) and 2483.5-2500 MHz (space-to-Earth) as a new Global Maritime Distress Safety Systems (GMDSS) satellite provider.” Of significant concern to the science services is the co- primary radio astronomy band at 1610.6-1613.8 MHz, which must receive adequate protection. In addition, the RAS band at 4990-5000 MHz is at risk from the second harmonic of part of the 2483.5-2500 MHz band. Recommendation ITU-R RA.769 gives the threshold level of interference detrimental to radio astronomy observations of −238 dBW/(m2 Hz) in the 1610.6-1613.8 MHz band and −241 dBW/(m2 Hz) in the 4990-5000 MHz band. Radio Astronomy Service As noted in Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items of Interest to the Science Services at the World Radiocommunication Conference 2019, WRC-19 Agenda Item 1.8: The 1610.6-1613.8 MHz band is used for spectral line observations of the hydroxyl radical (OH). The OH transition at rest frequency 1612 MHz is one of the most important spectral lines for RAS and is listed as such in Recommendation ITU-R RA.314-10. OH was the first cosmic radical to be detected at radio frequencies and continues to be a powerful research tool. In its ground state, the OH molecule produces four spectral lines at frequencies of approximately 1612, 1665, 1667, and 1720 MHz, all of which have been observed in emission and in absorption in our Milky Way galaxy, as well as in external galaxies. The study of OH lines provides information on a wide range of astronomical phenomena—for example, the formation of protostars and the evolution of stars. To interpret most observations made of the OH molecule, it is necessary to measure the relative strength of several of these lines. The loss of the ability to observe any one of these lines will prevent the study of these classes of physical phenomena. … One challenge for coordinated spectral sharing of this frequency range is that observations in the 1612 MHz band are sometimes conducted on targets of opportunity (e.g., particularly on objects such as comets, which have been observed to produce transient emissions in this line). Thus, the protection of the RAS band at 1610.6-1613.8 MHz requires careful consideration of compatibility, both in the context of in-band transmissions and unwanted spurious emissions into this band. In regards to the proposed 2483.5-2500 MHz (space-to-Earth) transmission, coordination with RAS is required by the mobile-satellite and the radiodetermination-satellite services in this band (RR 5.402) because the harmonics fall within the international secondary allocation of 4800-4990 MHz and the RAS co-primary allocation of 4990-5000 MHz. Note also that RAS has a co-primary allocation for 4950-4990 MHz in Argentina, Australia, and Canada (RR 5.443). Thus, since spaceborne and airborne transmissions are potentially serious sources of interference, similar coordination with RAS should be required if this band is allocated to the GMDSS. Observations in the 1612 MHz band and the 5 GHz band are carried out at a number of radio astronomy sites in numerous countries worldwide. In the United States, these include the Very Large PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 27

Array, the Green Bank Telescope, the Arecibo Observatory, 3 the Allen Telescope Array, and the 10 stations of the Very Long Baseline Array. Internationally, current facilities include the Nançay RadioHeliograph Telescope (France), Jodrell Bank (United Kingdom), MERLIN (United Kingdom), the 100-m Radio Telescope Effelsberg (Germany), the Westerbork Synthesis Radio Telescope (Netherlands), the stations of the European VLBI Network, the Medicina Radio Observatory (Italy), the 64-m Parkes Observatory (Australia), the Australia Telescope Compact Array (Australia), the Australian Square Kilometre Array Pathfinder (Australia), the stations of the Australian Long Baseline Array (Australia), MeerKAT (South Africa), FAST (China), the Russian VLBI network (Russia), the RATAN-600 (Russia), the ROT-54/2.6 (Armenia), and the Brazilian Decimetric Array (Brazil). Recommendation: The committee supports the modernization of the Global Maritime Distress and Safety System and the implementation of e-navigation. However, the radio astronomy band at 1610.6-1613.8 MHz must receive adequate and consistent protection from both in-band and unwanted emissions. The RAS band 4990-5000 MHz must be protected from the second harmonics of transmissions in the 2483.5-2500 MHz band. 3 While the former 305m telescope at Arecibo Observatory is no longer functional, a 12m radio telescope is operational at the site and the observatory remains open. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 28

AGENDA ITEM 1.12: EESS RADAR SOUNDERS AT 45 MHz Agenda Item 1.12 is “to conduct, and complete in time for WRC-23, studies for a possible new secondary allocation to the Earth exploration-satellite (active) service for spaceborne radar sounders within the range of frequencies around 45 MHz, taking into account the protection of incumbent services, including in adjacent bands, in accordance with Resolution 656 (Rev.WRC-19).” Resolution 656 (Rev. WRC-19) considers that “there is an interest in using active spaceborne sensors in the vicinity of 40-50 MHz for measurements of Earth’s subsurface to provide radar maps of subsurface scattering layers with the intent to locate water/ice/deposits [and] that spaceborne radars are intended to be operated only in either uninhabited or sparsely populated areas of the globe, with particular focus on deserts and polar ice fields, and only at nighttime from 3 a.m. to 6 a.m. locally.” Resolution 656 also recognizes “that the frequency range 40-50 MHz is allocated to the fixed, mobile, and broadcasting services on a primary basis; that the frequency range 40.98-41.015 MHz is used by the Space Research Service (SRS) on a secondary basis; that country footnotes to the Table of Frequency Allocations for the frequency range 40-50 MHz provide primary allocations for the aeronautical radionavigation and radiolocation services in certain parts of the world; that Recommendation ITU-R RS.2042-1 provides typical technical and operating characteristics for spaceborne radar sounder systems using the frequency range 40-50 MHz that should be used for interference and compatibility studies; [and] that Report ITU-R RS.2455-0 provides preliminary results of sharing studies between a 45 MHz radar sounder and incumbent fixed, mobile, broadcasting and space research services operating in the frequency range 40-50 MHz.” Earth Exploration-Satellite Service Low-frequency radar is the only known method for collecting high-resolution observations of Earth’s subsurface, such as root-zone soil moisture, water table in aquifers, and subsurface/multilayer ice deposits. It is estimated that approximately 30 percent of the world’s freshwater supply resides in underground aquifers and another 68 percent in glaciers, snow, and ice caps. As the world population increases and the global climate shifts toward drier and more water-stressed patterns, quantification of location and dynamics of these subsurface water resources becomes more critical. In particular, the knowledge of where aquifers are located and how they are being used, or conversely, where they are available but are not being used, will be an important element of managing this valuable resource for generations to come. Groundwater is and will continue to be a critical resource for agriculture and for domestic consumption, as well as for regulating the recharge component of the global water cycle. Radar systems operating in the tens of megahertz to hundreds of megahertz are needed for this purpose due to their ability to penetrate into the ground and carry back information to the radar receivers. The availability of an Earth exploration-satellite (active) service for spaceborne radar operation is therefore a crucial science and societal need. An Earth-orbiting radar satellite system is currently being considered in the 40- 50 MHz range, and more specifically with a center frequency of 45 MHz, for these purposes. Such a radar satellite mission is being considered for operations in a Sun-synchronous low Earth orbit (LEO) at an altitude of approximately 400 km. The mission would observe primarily areas having a prevalence of ice sheets, including Greenland and Antarctica, as well as the desertic areas of the Middle East and North Africa (MENA). The radar is expected to operate in a sounding mode, looking straight down in the nadir direction, with a vertical resolution of 5 to 7 m. It is expected that a mission duration of 18 months, with 10-minute daily instrument on-time, will be sufficient for establishing a baseline for observations of ice sheets and aquifers in the respective geographic locations. Given current scientific understanding of the rates of change in both ice sheets and aquifers, it is expected that such a mission will be repeated at least once each decade. According to the June 2019 ITU-R report, ITU-R RS.2455-0, the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 29

power flux density at Earth’s surface beneath the satellite track is estimated at −93.3 dBW/m2 at the center frequency of 45 MHz, with a 3dB bandwidth of 8 MHz. Considering the antenna patterns and the geometry of observations, the radiated power outside of the primary MENA observation region will be less than −130 dBW. Furthermore, it must be noted that the observations will occur almost exclusively in areas with little or no population density. To minimize the effects of the ionosphere on the radar signals (including Faraday rotation, scintillation, group delay, etc.), the operations will be planned for 3 a.m. to 6 a.m. daily, which is the time of least ionospheric activity. Besides the short duration of the daily radar on-time, the limited duration of the mission, and the limited geographic coverage area focused on sparsely populated areas, according to ITU-R RS.2455-0, the impact from this to incumbent services is minimal to none based on an analysis of maximum interference power levels. This analysis shows that the power levels radiated will be below the fixed, mobile, broadcasting, space research, and radiolocation services in polar and auroral regions. In middle latitudes, the power levels are at or slightly above the allowed interference levels for fixed and mobile services, though they can be up to 7 dB higher than the allowed limits for radionavigation services. Because of the limited temporal and spatial extent of the mission’s coverage, these results indicate that the prospective radar sounder mission at 45 MHz will have compatible operations with most existing services, and in the cases where the transmit signal level might exceed the allowed interference levels, operations may be modified accordingly to accommodate the minimum interference requirements. Radio Astronomy Service While RAS does not have allocations in the band under consideration, neighboring allocations are of concern, particularly because radar signals can be misinterpreted as natural transient emissions, potentially resulting in erroneous scientific conclusions based on data affected by radar interference. For example, the nearby 37.5-38.25 MHz band is allocated to the RAS worldwide on a secondary basis. This band is included in RR 5.149, which notes that emissions from space or airborne stations may be particularly serious sources of interference to the RAS and urges Administrations to protect the RAS from harmful interference. In the United States, the 37.5-38 MHz range is allocated to the RAS on a secondary basis, and the 38-38.25 MHz band is allocated to the RAS on a primary, shared basis with the Fixed and Mobile services. The entire 37.5-38.25 MHz band is included in footnote US342, the U.S. equivalent of RR 5.149. In Region 2, and in the United States in particular, the band 73-74.6 MHz is allocated to the RAS on an exclusive, primary basis. Internationally, the band is included in RR 5.149 and in the United States, it is included in footnote US246, which prohibits all emissions in the band. The detrimental interference level in the 74 MHz band, given in Recommendation ITU-R RA.769, is −259 dBW/(m2 Hz). While no value is given for the 38 MHz band in the Recommendation explicitly, the threshold in this band should be similar. Planned compatibility studies should include consideration of the impacts of an orbiting 45 MHz radar sounder on radio telescope facilities operating in the bands listed above, with particular attention given to out-of-band and spurious emissions, including harmonics. Examples of such facilities currently operating include the stations of the Long Wavelength Array (LWA) in New Mexico and California, LOFAR in the Netherlands (which includes other stations elsewhere in Europe), NenuFAR in France, and the Murchison Widefield Array (MWA) and SKA prototype antennas located in Australia. The interest in developing a new EESS (active) system at 45 MHz coincides with an increased interest in radio astronomy observations in this frequency region. Examples of recent discoveries from these bands include intrinsic radio emissions from fireballs (i.e., large meteors), observed by the LWA, that are the subject of ongoing studies at other locations. Additionally, precise and accurate observations of the microwave background temperature in these bands are critical for the calibration of higher-frequency (100-200 MHz) observations used to study various cosmological issues, including the Cosmic Dawn. This increased focus on this spectral region for radio astronomy observations has resulted in considerable interest in developing new radio astronomy observatories targeting these bands. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 30

Suitable coordination should allow for complete compatibility between an orbiting EESS (active) radar sounder at 45 MHz and the radio astronomy facilities described above. Some complications arise in that the ionospheric stability that makes the 3 a.m. to 6 a.m. local-time window attractive for EESS sounding also makes it an optimal time for astronomical observations. Similarly, surface propagation characteristics make desert areas an attractive location for future astronomy facilities. Notwithstanding those issues, the limited duty cycle anticipated for the EESS (active) sensors should readily enable sufficient compatibility, provided suitable coordination agreements are in place. Recommendation: The committee supports the potential allocation of spectrum for a spaceborne radar sounder within the frequency range 40-50 MHz. Coordination between the use of a satellite- based radar system and radio astronomy should be explored to determine optimal times of satellite overpasses over the areas of interest, sidelobe suppression requirements, and other system and operating parameters that enable effective coordination of all these services. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 31

AGENDA ITEM 1.13: ALLOCATIONS TO THE SPACE RESEARCH SERVICE Agenda Item 1.13 proposes “to consider a possible upgrade of the allocation of the frequency band 14.8-15.35 GHz to the space research service, in accordance with Resolution 661 (WRC-19).” Resolution 661 (WRC-19) invites sharing and compatibility studies in the frequency band 14.8-15.35 GHz with proposed broadband communication downlinks in the SRS. As noted in Resolution 661 (WRC- 19), the frequency band 15.2-15.35 GHz is currently allocated to EESS (passive) and SRS (passive) on a secondary basis and the adjacent frequency band 15.35-15.4 GHz is allocated to EESS (passive), RAS, and the SRS (passive) on a primary basis. The adjacent allocations for RAS and EESS at 15.35-15.4 GHz are protected by RR 5.340, which states that all emissions are prohibited in the band. The threshold for harmful interference listed in Recommendation ITU-R RA.769 is −233 dBW/(m2 Hz) for radio astronomy continuum observations at 15.375 GHz. Although there are no current EESS missions operating at this frequency band, the appropriate protection levels for EESS at 15.2-15.4 GHz is −169 dBW in a 50 MHz bandwidth, as noted in Recommendation ITU-R RS.2017. Radio Astronomy Service The primary concern for RAS is the potential for radio frequency interference from out-of-band emission (OOBE) from transmissions at the adjacent band. Under RR 5.340, no emission is allowed in the frequency range of 15.35-15.4 GHz, except those provided by RR 5.511, in which 15.35-15.4 GHz is also allocated to the fixed and mobile services on a secondary basis within a few specified countries. As noted above for Agenda Item 1.10, the frequency bands proposed for study in this agenda item are utilized for a range of both radio continuum and line observations. Radio continuum observations, which require large unpolluted bands of frequency, are essential in the K bands (Ku, K, Ka) for measuring free- free (Bremsstrahlung) radiation generated in ionized gas. Frequencies in the K bands are the least contaminated by dust emission (which peaks at higher frequencies) and synchrotron emission (which peaks at lower frequencies). In essence, continuum observations in the K band are effectively the only way to cleanly observe ionized gas that is optically obscured. This ability is essential for probing areas of star formation throughout the Milky Way and the universe. A number of important molecules also have transitions in frequency bands affected by this agenda item. These include ammonia, formaldehyde, methanol, and radio recombination lines (of both hydrogen and carbon). Ammonia was in fact the first polyatomic molecule detected in space. It has transitions that are commonly used to trace kinematics and measure temperatures in the interstellar medium and star- forming regions. These measurements require observing a number of transitions. Radio recombination lines (RRLs), including those of both hydrogen and carbon, are the only way of measuring ionization in interstellar space directly. With a set of RRLs across a range of frequencies, it is also possible to determine the density of the medium from which they are emitted. Of particular concern are the ammonia line at 15.391 GHz, the carbon recombination line at 15.351 GHz, and the hydrogen recombination line at 15.360 GHz, which are included in the RAS-allocated band adjacent to the frequencies considered in this agenda item. The wealth of information derived from observations of these and other spectral lines provide insight into the formation, structure, and physical properties of molecular clouds in both the Milky Way and nearby galaxies. International telescopes that operate at these frequencies include the following: HartRAO (South Africa), Nanshan (China), Tian Ma (China), Nobeyama Radio Observatory (Japan), VERA (Japan), Badary Radio Astronomical Observatory (Russia), Australia Telescope Compact Array (Australia), Mopra Radio Telescope (Australia), Mount Pleasant Radio Telescope (Tasmania), Radioastronomical Observatory (Russia), Svetloe Radio Astronomical Observatory (Russia), VLBI (Italy), MERLIN (England), Metsähovi Radio Observatory (Finland), Onsala Space Observatory (Sweden), São Gião Radio PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 32

Telescope (Portugal), Very Large Array (USA), Green Bank Telescope (USA), and the 10 stations of the Very Long Baseline Array (USA). Recommendation: The committee urges that the adjacent 15.35-15.4 GHz passive band be protected from out-of-band emissions if the 14.8-15.35 GHz Space Research Service allocation is upgraded to primary status. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 33

AGENDA ITEM 1.14: ALLOCATIONS TO THE EARTH EXPLORATION-SATELLITE SERVICE IN 231.5-252 GHz Agenda Item 1.14 considers “possible adjustments of the existing or possible new primary frequency allocations to EESS (passive) in the frequency range 231.5-252 GHz, to ensure alignment with more up- to-date remote-sensing observation requirements, in accordance with Resolution 662 (WRC-19).” Agenda Item 1.14, and the resolution it cites, proposes a reassessment of the EESS (passive) assignments in the 231.5-252 GHz range, in light of plans to develop and launch new spaceborne instrumentation measuring in this region. There are existing primary allocations to EESS (passive) in the 235-238 GHz and 250-252 GHz bands, with the latter having all emissions prohibited (RR 5.340). Note that the immediately adjacent 226-231.5 GHz region also has a primary allocation to EESS (passive) and RR 5.340 protection. Recommendation ITU-R RS.2017 indicates threshold levels of interference in this spectral region are −194 dBW in 3 MHz for limb-sounding instruments, with the same −194 dBW limit applying to 200 MHz bandwidth in nadir/conical viewing instruments. In addition, there are existing primary RAS allocations at 241-248 GHz and 250-252 GHz and a secondary allocation to RAS at 248- 250 GHz. RR 5.149 recommends that RAS be protected from harmful interference over the entire spectral interval from 241-250 GHz. The threshold level for harmful interference to radio astronomy continuum observations at these frequencies is −218 dBW/(m2 Hz), as listed in Table 1 of Recommendation ITU-R RA.769. It is important to note that RAS and passive EESS are mutually compatible. Earth Exploration-Satellite Service This spectral region is used for remote sounding of atmospheric composition by limb viewing low- Earth-orbiting sensors. Specifically, the 235-238 GHz region is dominated by emission from atmospheric ozone and includes the spectral line targeted by existing and planned instruments tracking the recovery of Earth’s fragile ozone layer in response to the Montreal protocol to ban the production of ozone-depleting substances. The adjacent 226-231.5 GHz region contains a line for carbon monoxide (CO), a unique and widely used tracer of atmospheric motions and the most common marker of air polluted by biomass burning and/or industrial emissions. Compared to many atmospheric trace gases, CO has very few widely separated lines in the microwave spectrum, making this spectral regional particularly critical. Importantly, and in contrast with instruments measuring at shorter wavelengths (e.g., infrared and ultraviolet), microwave sounders are able to observe these trace gases in the presence of both clouds and aerosols (small particles of soot, salt, sulfate, etc.). Such aerosols are often co-emitted with CO, which makes observing gas-phase composition observations in polluted regions particularly challenging with shorter- wavelength instruments, underscoring the unique value of microwave measurements. More recently, the potential of this spectral region to provide unique information on cloud ice particles in the middle and upper troposphere (~5 km and above) is gaining attention, and plans are underway to exploit this information. Such ice clouds are an important and poorly understood aspect of the atmosphere system and represent a significant uncertainty on climate projections. A spaceborne sensor under development will provide measurements of ice cloud signatures in this spectral region and likely provides the motivation for this agenda item. Importantly, such measurements do not employ limb- viewing, instead favoring conical and/or cross-track scanning. This increases the likelihood of observations down to the surface, making RFI a potentially much greater impediment to such observations. Further, in contrast with gas-phase chemistry observations, clouds are far more spatially heterogeneous, presenting a challenge to any techniques used to excise RFI-contaminated scenes based on assumptions that RFI sources would be localized. Currently, the Aura Microwave Limb Sounder (MLS) makes measurements in multiple 1.5 GHz-wide bands in this region. The frequency range is also planned for future observation by the European ICI suite of instruments. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 34

Radio Astronomy Service The 231.5-252 GHz spectral region lies within the 1.3 mm radio astronomy band, which is of vital importance for studying the physics and chemistry of the universe. This band contains a wealth of molecular lines that enable astronomers to trace the motions and chemical properties of star-forming clouds and protoplanetary disks. In certain cases, these studies involve the same molecular species, such as CO and NO, that are important to Earth remote sensing. In particular, CO is the single most important species used by radio astronomers to trace the molecular universe due to its relative high abundance and low excitation energy. The 1.3 mm band also lies near the spectral peak of the cosmic microwave background (CMB) radiation and is of great value for mapping thermal emission from cool, dusty objects. Reflecting this scientific importance, the 1.3 mm band includes a number of existing RAS allocations. As noted above, there are RAS primary allocations at 241-248 GHz and 250-252 GHz, containing spectral lines of the molecules CS and NO respectively, and a secondary allocation at 248-250 GHz. In addition, the adjacent RAS primary allocation 226-231.5 GHz contains the vitally important CO line at 230.538 GHz and could be vulnerable to OOBE from active services in the allocations from 231.5-235 GHz, should these see significant future development. Table 2.3 lists worldwide RAS facilities currently equipped with receivers covering the 1.3 mm band. These observatories represent a multi-billion dollar capital investment and are routinely over-subscribed for observing time. Most of the observatories in Table 2.3 participate in global VLBI experiments in this band such as the Event Horizon Telescope, which recently imaged the black hole at the center of the nearby galaxy M87, resolving such an object for the first time and capturing the worldwide public imagination. In addition to general-purpose radio observatories, more specialized observatories such as the BICEP- Keck experiment at the South Pole and the Simons Observatory instruments in northern Chile are dedicated to mapping the structure of the CMB, providing a window into the universe shortly after its creation that enables quantitative tests of Big Bang cosmology. Several of these experiments include detector arrays operating in the 1.3 mm band. CMB experiments typically operate with wide bandwidths covering RAS-allocated and unallocated spectrum, but the availability of protected spectrum aids identification and mitigation of interference. Recommendation: The committee welcomes the re-evaluation of these assignments and recommends that it be undertaken in collaboration with Earth scientists targeting this spectral region for atmospheric chemistry and atmospheric cloud ice applications. Adding EESS (passive) as co- primary to the existing RAS primary allocation at 241-248 GHz, and possibly expanding this allocation into adjacent bands, is an efficient way to support and protect new EESS (passive) ice- cloud-sensing applications needed to advance weather forecasting and climate studies. Related adjustments and development of rules for non-passive allocations in adjacent bands should take into account the high sensitivity of RAS and EESS (passive) applications in the 1.3 mm band to out-of- band and spurious emissions. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 35

TABLE 2.3 RAS Facilities Operating in the 1.3 mm Band Latitude Longitude Altitude Facility Location (deg N) (deg E) (m) Arizona Radio Observatory Kitt Peak 12m Arizona, USA 32.0 −111.6 1895 Telescope (ARO KP12m) Arizona Radio Observatory Submillimeter Arizona, USA 32.7 −109.9 3160 Telescope (ARO SMT) Atacama Large Millimeter/submillimeter Array Chile −23.0 −67.8 5075 (ALMA) Atacama Pathfinder Experiment (APEX) Chile −23.0 −67.8 5105 Greenland Telescope (GLT) Greenland 76.5 −68.7 90 IRAM 30-meter Spain 37.1 −3.4 2920 James Clerk Maxwell Telescope (JCMT) Hawaii, USA 19.8 −155.5 4120 Large Millimeter Telescope (LMT) Mexico 19.0 −97.3 4595 NANTEN2 Chile −23.0 −67.7 4800 Northern Extended Millimeter Array (NOEMA) France 44.6 5.9 2620 Submillimeter Array (SMA) Hawaii, USA 19.8 −155.5 4115 South Pole Telescope Antarctica −90.0 0 2815 NOTE: Acronyms are defined in Appendix B. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 36

AGENDA ITEM 1.15: GSO EARTH STATIONS IN MOTION IN THE FSS 12.75-13.25 GHz Agenda Item 1.15 is “to harmonize the use of the frequency band 12.75-13.25 GHz (Earth-to-space) by Earth stations on aircraft and vessels communicating with geostationary space stations in the fixed satellite service globally, in accordance with Resolution 172 (WRC-19).” Resolution 172 (WRC-19) considers “c) that the frequency band 12.75-13.25 GHz is currently allocated on a primary basis to the fixed, fixed-satellite (FSS) (Earth-to-space) and mobile services, and on a secondary basis to the space research (deep space) (space-to-Earth) service globally,” and “d) that the frequency band 12.75-13.25 GHz is used by the geostationary-satellite (GSO) FSS in accordance with the provisions of Appendix 30B (No. 5.441) and there are many existing GSO FSS satellite networks operating in this frequency band.” It further considers that “there is an increased need for in-flight and maritime connectivity which can be partially satisfied by allowing Earth stations on aircraft and vessels to communicate with GSO space stations in the FSS, including in the frequency band 12.75-13.25 GHz (Earth-to-space).” Accordingly, it invites ITU-R to “study the sharing and compatibility issues between Earth stations on aircraft and vessels communicating with GSO space stations in the FSS and current and planned stations of existing services referred to in considering c) as well as services in adjacent frequency bands, to ensure protection of, and not impose undue constraints on, those services and their future development, taking into account the provisions of Appendix 30B.” Of particular concern for the scientific services is the potential for out-of-band emissions into the adjacent EESS (active) allocation at 13.25-13.75 GHz. Recommendation ITU-R RS.1166-4 provides detailed performance interference criteria for EESS (active) sensors, including those in the 13.25-13.75 GHz band. Specifically, for altimetry, an aggregate interference threshold of −117 dB(W/320 MHz) is recommended. For scatterometer systems, an interference criterion of −161 dBW over any 2 kHz bandwidth within the 1 MHz bandwidth of the sounder is recommended. Finally, in the case of precipitation radars, the recommended interference limit is −150 dB(W/600 kHz) in the 12 MHz band between 13.793 and 13.805 GHz, with successively looser limits in the spectral regions beyond (see Section 4.1.2 of ITU-R RS.1166-4 for details). Earth Exploration-Satellite Service The 13.25-13.4 GHz and 13.4-13.75 GHz frequency bands are used for active EESS remote sensing with altimeters, scatterometers and precipitation radars. Primary mission objectives for altimeters are sea- ice elevation, sea-ice thickness, geoid and ocean dynamic topography (currents), and significant wave height. Primary mission objectives for scatterometers are ocean surface wind speed and vector winds. Secondary mission objectives for scatterometers include biomass, plant growth and phenology, sea-ice type, and snow cover. Ocean surface winds are critical elements that couple the ocean to the atmosphere, driving oceanic circulation and wind waves and exerting a momentum drag on the atmosphere. They strongly influence the fluxes of heat, gas, and momentum across the air-sea interface. In the short term, these processes have significant impact on weather and significant waves, and, in the long term, they affect regional and global climates. Similarly, sustained measurements of sea-ice elevation, sea-ice thickness, and ocean currents are important for understanding and predicting longer-term variations in atmospheric and global circulations. Altimeters generally use a center frequency around 13.5 GHz with bandwidths of around 500 MHz to achieve the desired measurement precision. Scatterometers operate around 13.25 GHz and 100 MHz bandwidth is sufficient to meet the desired measurement resolution requirements. For precipitation radars, the primary mission objectives are measurements of the effective radii of cloud ice and cloud liquid water and total atmospheric column amounts of cloud ice and cloud liquid water. Precipitation radars operate near 13.6 GHz and need a total of 20-40 MHz bandwidth to achieve PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 37

their measurement objectives. These frequencies are key to observing precipitation and rain or snow particles in three dimensions (vertical profiles along with horizontal structure). This information is critical for understanding cloud structures and improving weather and climate forecasting models. The 13.6 GHz active radar channel on NASA’s Global Precipitation Measurement (GPM) satellite operates between 13.597 and 13.603 GHz. Any out of band emissions into these critical frequencies would seriously hamper the collection of this important EESS data. Emissions that would be especially concerning are OOBE Earth-to-space transmissions, as these would cause RFI problems for the GPM radar. Table 2.4 lists EESS (active) sensors measuring in the 13.25-13.75 GHz frequency bands. Recommendation: The committee urges that any sharing studies embarked upon under Agenda Item 1.15 explicitly consider the threshold limits in Recommendation ITU-R RS.1166-4 and recommend suitable out-of-band emission masks and/or guard bands to ensure they are met. TABLE 2.4 EESS (Active) Sensors Measuring in the 13.25-13.75 GHz Frequency Bands Center Frequency IFOVa Sensor Agency and Satellite (GHz) (km) Altimeter JAXA COMPIRA 13.56 and 5.3 20 SIRAL Altimeter ESA CryoSat-2 13.56 15 WindRAD CMA FY-3E 13.265 and 5.3 25 (Ku band); Scatterometer 10 (C band) DPR Precipitation radar NASA GPM Core 13.6 and 35.55 5 Scatterometer NSOAS HY-2A-2H 13.25 25 Altimeter NSOAS HY-2A-2H 13.580 and 5.3 16 SRAL Altimeter NASA JASON-3/JASON-A/B 5.3 and 13.58 20 (300 m in SAR mode) OSCAT and ScatSat ISRO OceanSat-2/3 13.515 25 Scatterometer SRAL Altimeter ESA Sentinel-3A/D 13.58 and 5.4 20 (300 m in SAR mode) Airborne APR-2 Aircraft-based 13.4 1 km max. Precipitation radar SWIM Altimeter CNSA CFOSAT 13.575 18 SCAT Scatterometer CNSA CFOSAT 13.256 10 SWOT Altimeter NASA (planned) 13.58 and 5.3 25 Rainradar CMA FY-3G 13.35 and 35.55 TBD Precipitation radar NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Instantaneous field-of-view dimensions. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 38

AGENDA ITEM 1.16: NON-GSO EARTH STATIONS IN MOTION Agenda Item 1.16 is “to study and develop technical, operational and regulatory measures, as appropriate, to facilitate the use of the frequency bands 17.7-18.6 GHz and 18.8-19.3 GHz and 19.7-20.2 GHz (space-to-Earth) and 27.5-29.1 GHz and 29.5-30 GHz (Earth-to-space) by non-GSO FSS Earth stations in motion, while ensuring due protection of existing services in those frequency bands in accordance with Resolution 173 (WRC-19).” Resolution 173 lists the various services currently allocated to the above-mentioned bands and cites “a need for mobile-satellite communications, including global satellite broadband,” which can be met in part by “allowing Earth stations in motion (ESIMs) to communicate with FSS space stations operating in the frequency bands” detailed above. The resolution resolves to invite the ITU to “study sharing and compatibility between ESIMs operating with non-GSO FSS systems and current and planned stations of primary services allocated in the frequency bands 17.7-18.6 GHz, 18.8-19.3 GHz and 19.7-20.2 GHz (space-to-Earth) and 27.5-29.1 GHz and 29.5-30 GHz (Earth-to-space), or parts thereof, to ensure protection of, and not impose additional constraints on, GSO systems and other services, including terrestrial services, in those frequency bands and in adjacent frequency bands, including passive services.” While there are no direct conflicts in any of these frequency bands, the 17.7-18.6 GHz and 18.8-19.3 GHz bands bracket the 18.6-18.8 GHz band, which is allocated to EESS (passive) on a primary basis and is used for a wide range of ocean- and land-related remote sensing. The ITU-R RS.2017 recommended interference threshold for this frequency band is −163 dBW in 200 MHz bandwidth. Earth Exploration-Satellite Service In conjunction with measurements at 6, 10, and 37 GHz, observations in the 18.6-18.8 GHz band are used over ocean areas to retrieve surface wind speed (and direction for polarimetric microwave radiometers) from ocean surface roughness. This band also contributes information to measurements of over-ocean rain rate (in conjunction with information derived from other bands ranging from 10 to 90 GHz) and sea-surface temperature (for which it reduces uncertainty related to surface roughness). The polarization of observed 18 GHz signals provides information on sea-ice concentration (in conjunction with measurements across many other bands from 1.4 to 90 GHz). Remote sensing of land properties also makes heavy use of 18.6-18.8 GHz measurements, with snow cover and snow water equivalent (SWE) estimated from 18 GHz observations in conjunction with measurements at 6.6, 10, 37, and 90 GHz. Similarly, mapping of continental ice relies on 18 GHz measurements along with those in other bands from 1.4 to 90 GHz. Estimates of over-land rain rate derive from measurements from 10 to 180 GHz, with the 18 GHz information being particularly valuable for observing extreme precipitation associated with severe weather events. It is important to note that operational weather forecasting systems use information from the 18.6- 18.8 GHz band and other bands as a combined system. Strong interference in this band reduces the measurement quality for all of the geophysical variables described above, even if other bands are interference free. Worse, if the impact of interference is large enough to give incorrect information, but not so large as to be clearly identifiable and removed, weather forecasting systems will be fed incorrect information, jeopardizing the accuracy of their predictions. Table 2.5 lists the various spaceborne sensors observing in the 18.6-18.8 GHz band. Many of these sensors are used in operational weather forecasting systems to compute information on these parameters described above. Agenda Item 1.16 is examining the expanded use of the 17.7-18.6 GHz and 18.8-19.3 GHz bands for space-to-Earth links. Accordingly, the risk to EESS (passive) observations from out-of-band emissions associated with these links derives from signals reflected off Earth’s surface rather than direct-beam or side-lobe signals. Although this geometry likely reduces the power of the interfering signals, it has the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 39

potential to increase the geographical area over which EESS (passive) observations are affected, compared to an Earth-to-space geometry for which “point sources” can be more readily identified and excised. Further, strong specular reflections of satellite emissions by surfaces such as sea ice (as has been documented in other bands) have the potential to render measurements at 18.6-18.8 GHz invalid in the very geographical regions, and under the specific geophysical conditions, where they provide uniquely valuable information. Furthermore, EESS (passive) sensors are “self-calibrating,” in that some portion of the observing time is spent viewing cold outer-space signals. These provide a “cold” or “zero level” background signal that is used in conjunction with a “hot” view (typically an internal target or noise source) to calibrate the instrument in real time, thereby correcting for variations in gain, etc. Accordingly, direct-beam coupling of non-GSO emissions into the “space view” of EESS (passive) sensors has the potential to corrupt multiple adjacent EESS (passive) observations by invalidating the instrument calibration. TABLE 2.5 EESS (Passive) Sensors Measuring in Bands Close to 18.6-18.8 GHz Center Frequency (GHz) and Bandwidth IFOVb a Sensor Satellite polarization (MHz) (km) AMSR2 JAXA GCOM-W1 18.7 V,H 200 14 × 22 GMI NASA GPM 18.7 V,H 200 6 × 13.4 WindSat DoD Coriolis 18.7 V,H,3,4 750 12.5 × 12.5 AMR-C NOAA Jason-2 and 3 18.7 V (nominal, 200 25 with H backup) MWI EUMETSAT MetOp-SG 18.7 V,H 200 50 MTVZA-GY RosHydroMet Meteor-M 18.7 V,H 200 32 × 32 MWRI CMA FY-3 18.7 V,H 200 30 × 50 MWRI NSOAS HY-2A 18.7 V,H 250 30 × 45 SSM/I DoD DMSP-F15 19.35 V,H 250 45 × 68 SSMIS DoD DMSP-F16 to F-19 19.35 V,H 357 42.4 × 70.1 MWI DoD WSF-M 18.85 V,H,3,4 500 15 × 23 CIMR Copernicus 18.7 V,H,3,4 200 ≤5.5 AMSR3 JAXA GOSAT-GW 18.7 V,H 200 14 × 22 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Polarization codes are H-horizontal, V-vertical, 3 and 4—3rd and 4th components of the Stokes vector. b Instantaneous field-of-view dimensions Recommendation: The committee urges that any consideration of new or revised allocations to the 17.6-18.6 and 18.8-19.3 GHz bands explicitly consider the impact to the 18.6-18.8 GHz band, which is allocated to EESS (passive) on a primary basis. Out-of-band emission masks and/or guard bands should be required to ensure that the ITU-R RS.2017 interference threshold, in the aggregate, of −163 dBW in 200 MHz is not exceeded in that band. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 40

AGENDA ITEM 1.17: INTER-SATELLITE LINKS AT 11.7-12.7 GHz, 18.1-18.6 GHz, 18.8-20.2 GHz, AND 27.5-30 GHz Agenda Item 1.17 is “to determine and carry out, on the basis of the ITU-R studies in accordance with Resolution 773 (WRC-19), the appropriate regulatory actions for the provision of intersatellite links in specific frequency bands, or portions thereof, by adding an inter-satellite service allocation where appropriate.” Resolution 773 (WRC-19) invites the ITU-R to study the technical and operational characteristics of stations that intend to operate in the bands referenced in the Resolution. The resolves most relevant to the passive services calls for the study of sharing and compatibility between satellite-to-satellite links intending to operate between space stations in the frequency bands 11.7-12.7 GHz, 18.1-18.6 GHz, 18.8- 20.2 GHz, and 27.5-30 GHz and current and planned stations of the FSS and other existing services allocated in the same frequency bands and adjacent frequency bands, including passive services. While there are no direct conflicts in any of these frequency bands, the 17.7-18.6 GHz and 18.8-19.3 GHz bands bracket the 18.6-18.8 GHz band, which is allocated to EESS (passive) on a primary basis and is used for a wide range of ocean- and land-related remote sensing. The ITU-R RS.2017 recommended interference threshold for this band is −163 dBW in 200 MHz bandwidth. Earth Exploration-Satellite Service As noted above regarding Agenda Item 1.16, observations in the 18.6-18.8 GHz band are used, in conjunction with measurements at 6, 10, and 37 GHz, to compute surface wind speed (and direction for polarimetric microwave radiometers) over oceans, derived from ocean surface roughness. This band also contributes information to measurements of over-ocean rain rate (in conjunction with information derived from other bands ranging from 10 to 90 GHz) and sea-surface temperature (for which it reduces uncertainty related to surface roughness). The polarization of observed 18 GHz signals provides information on sea-ice concentration (in conjunction with measurements across many other bands from 1.4 to 90 GHz). Remote sensing of land properties also makes extensive use of 18.6-18.8 GHz information, with snow cover and snow water equivalent (SWE) estimated from 18 GHz observations in conjunction with measurements at 6.6, 10, 37, and 90 GHz. Similarly, mapping of continental ice relies on 18 GHz measurements along with those in other bands from 1.4 to 90 GHz. Estimates of over-land rain rate derive from measurements from 10 to 90 GHz, with the 18 GHz information being particularly valuable for observing extreme precipitation associated with severe weather events. It is important to note that operational weather forecasting systems use information from the 18.6- 18.8 GHz band and other bands as a combined system. Strong interference in this band reduces the measurement quality for all of the geophysical variables described above, even if other bands are interference free. Worse, if the impact of interference is large enough to give incorrect information, but not so large as to be clearly identifiable and removed, weather forecasting systems will be fed incorrect information, jeopardizing the accuracy of their predictions. Table 2.6 lists the various spaceborne sensors observing in the 18.6-18.8 GHz band, information from many of which is used in operational weather forecasting systems to compute the parameters described above. Agenda Item 1.17 is examining use of the 17.7-18.6 GHz and 18.8-19.3 GHz bands (among others) for space-to-space links. Such links likely include those among GSO satellites, among “non-GSO” satellites (i.e., those in low- or mid-Earth orbit), and between these two groups. As with Agenda Item 1.16, a particular concern is the impact of signals reflected off Earth’s surface and into the beam of orbiting EESS (passive) sensors, most likely to occur in GSO-to-non-GSO and non-GSO-to-non-GSO transmissions. Reflection from non-GSO satellites are harder to predict and account for than those from PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 41

GSO transmitters, given that, in the non-GSO case, both the transmitter and the receiver are in motion relative to Earth’s surface. Furthermore, EESS (passive) sensors are “self-calibrating” in that some portion of the observing time is spent viewing cold outer-space signals. These provide a “cold” or “zero level” background signal used, in conjunction with a “hot” view (typically an internal target or noise-source), to calibrate the instrument in real time, correcting for variations in gain, etc. Accordingly, direct-beam coupling of non-GSO emissions into the “space view” of EESS (passive) sensors has the potential to corrupt many successive EESS (passive) observations by invalidating the instrument calibration. Unique to the WRC-23 agenda, Agenda Item 1.17 raises the crucial concern that an orbiting EESS (passive) sensor risks suffering irreversible damage should a nearby (e.g., within a few kilometers) non- GSO transmitter enter its field-of-view, with its signals directed toward the EESS instrument. While such conjunctions are likely to be rare, their frequency will only increase as the number of non-GSO transmitters proliferate. Given that EESS sensors are generally considered to be national assets, it is essential that the scope for such damage be assessed and steps taken to eliminate the associated risk should the allocations envisioned in this agenda item be enacted. TABLE 2.6 EESS (Passive) Sensors Measuring Bands in and around 18.6-18.8 GHz Center Frequency (GHz) and Bandwidth IFOVb Sensor Satellite Polarizationa (MHz) (km) AMSR2 JAXA GCOM-W1 18.7 V,H 200 14 × 22 GMI NASA GPM 18.7 V,H 200 6 × 13.4 WindSat DoD Coriolis 18.7 V,H,3,4 750 12.5 × 12.5 AMR-C NOAA Jason-2 and 3 18.7 V (nominal, 200 25 with H backup) MWI EUMETSAT MetOp-SG 18.7 V,H 200 50 MTVZA-GY RosHydroMet Meteor-M 18.7 V,H 200 32 × 32 MWRI CMA FY-3 18.7 V,H 200 30 × 50 MWRI NSOAS HY-2A 18.7 V,H 250 30 × 45 SSM/I DoD DMSP-F15 19.35 V,H 250 45 × 68 SSMIS DoD DMSP-F16 to F-19 19.35 V,H 357 42.4 × 70.1 MWI DoD WSF-M 18.85 V,H,3,4 500 15 × 23 CIMR Copernicus 18.7 200 ≤5.5 AMSR3 JAXA GOSAT-GW 18.7 V,H 200 14 × 22 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Polarization codes are H-horizontal, V-vertical, 3 and 4-3rd and 4th components of the Stokes vector. b Instantaneous field-of-view dimensions. Recommendation: The committee urges that any consideration of new or revised allocations to the 17.6-18.6 and 18.8-19.3 GHz bands explicitly consider the impact to the 18.6-18.8 GHz band, which is allocated to EESS (passive) on a primary basis. Out-of-band emission masks and/or guard bands should be required to ensure that the ITU-R RS.2017 interference threshold of −163 dBW in 200 MHz is not exceeded in that band. Studies of the potential for irrevocable damage to EESS (passive) sensors from cases where a non-GSO transmitter and an EESS (passive) sensor are in close proximity, with their beams aligned, and of strategies to eliminate the risk of such damage, must be completed before decisions are made on Agenda Item 1.17. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 42

AGENDA ITEM 1.19: FSS 17.3-17.7 GHz IN REGION 2 Agenda Item 1.19 is “to consider a new primary allocation to the fixed-satellite service in the space- to-Earth direction in the frequency band 17.3-17.7 GHz in Region 2, while protecting existing primary services in the band, in accordance with Resolution 174 (WRC-19).” Resolution 174 invites sharing and compatibility studies between FSS (space-to-Earth) “in order to consider a possible new primary allocation to the FSS (space-to-Earth) in the frequency band 17.3-17.7 GHz for Region 2, while ensuring the protection of existing primary allocations in the same and adjacent frequency bands, as appropriate.” Of concern for the scientific services is the adjacent EESS (active) allocation at 17.2-17.3 GHz. Earth Exploration-Satellite Service Knowledge of snow water equivalent (SWE), or how much water is contained in the snow mass, is of major importance in the local, regional, and global studies of the water cycle, water availability, ecosystem services, and for monitoring climate change and operational applications such as hydrological modeling and runoff prediction. Some of the priority questions that must be answered concern (1) the total amount of water stored in the form of snow and its variations on seasonal and interannual scales and (2) impacts of such stores and dynamics on the water and energy cycles and freshwater availability. Despite its critical importance, SWE/snow mass remains poorly observed on multiple spatial and temporal scales. Radar remote sensing observation concepts that could lead to the quantification of SWE and snow mass are, however, being developed and have shown success in several proof-of-concept demonstrations. These observations are most effectively performed at two distinct frequencies that can provide sensitivity to both the SWE and the snow microstructure, thus allowing the retrieval of both types of information simultaneously. One of these two frequencies must be in the Ku band range, with 17.2-17.3 GHz being the frequency band of choice for radar (EESS) operations. The other frequency can be lower—for example, 13.5 GHz or 9.5 GHz. These specific frequencies are needed due to the microstructure of snow (frozen water particles and air) and their specific scattering interactions with coincident microwave frequencies. Frequencies that are much lower would not be sensitive to SWE, especially if snow thickness is small. Frequencies that are much higher will not penetrate the snow layer and therefore will not provide the needed information about the total snow mass. Several studies are currently ongoing for development of such dual-frequency radar systems for SWE and snow mass observations. NASA is supporting several dual-frequency airborne radar developments, including that of SnowSAR (9.5 GHz and 17.2-17.3 GHz), a dual-frequency Ku band radar for snow (13.5 GHz and 17.2 GHz), an instrument incubator program project for the Wideband Instrument for Snow Measurements (WISM, 9.5 GHz and 17.2 GHz), and ground-based radar observations in the same frequency bands used during the SnowEx series of experiments. The frequency band 17.2-17.3 GHz is, therefore, a critical band for snow cover and SWE observations. Any adjacent services must be designed to protect this band for future airborne and spaceborne EESS operations for this Earth system variable. Recommendation: The committee recommends quantitative analyses of the potential impact of the planned transmit power levels by the fixed-satellite service in the 17.3-17.7 GHz band, which is adjacent to the EESS (active) band at 17.2-17.3 GHz. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 43

AGENDA ITEM 9.1a: REVIEW OF SPACE WEATHER SENSORS Agenda Item 9.1a states as follows: “[i]n accordance with Resolution 657 (Rev.WRC-19), review the results of studies relating to the technical and operational characteristics, spectrum requirements and appropriate radio service designations for space weather sensors with a view to describing appropriate recognition and protection in the Radio Regulations without placing additional constraints on incumbent services.” Space weather monitoring and prediction is crucial for basic research into Earth’s extended atmosphere and for mitigating impacts that could reach into the trillions of dollars on important terrestrial systems, including precision positioning, navigation, and timing applications, power grids, transionospheric communications, and human spacefaring activities. Research on space weather has been endorsed by many nations, including the U.S. National Science and Technology Council’s Space Weather Strategy and Action Plan. A comprehensive document (ITU-R RS.2456-0) has been issued by Working Party 7C surveying the myriad number of sensor systems at radio frequencies, both passive and active, for monitoring space weather effects, including detection of solar activity and the impact of this activity on Earth’s atmosphere and geospace regions. At a fundamental level, avoiding adverse interference impacts on space weather sensors remains a challenging task in light of the very large range of frequencies and the technique diversity of these sensing systems as revealed in RS.2456-0’s survey. Earth Exploration-Satellite Service A particular concern for this agenda item is the impact of out-of-band emissions and harmonics on space weather monitors for ionosphere, plasmasphere, and magnetosphere characterization, as enumerated in ITU-R RS.2456-0. The potentially affected sensors include passive systems such as L band radionavigation-satellite service (RNSS) monitors for radio scintillation and ionosphere/plasmasphere total electron content determination, ionospheric absorption monitors (riometers) at HF and VHF, VHF and UHF ionospheric tomographic beacon receiver systems, and VLF (3-30 kHz) sensors for magnetospheric and ionospheric diagnostics. Active ground-based space weather sensors listed in ITU-R RS.2456-0 include ionospheric HF sounders and atmospheric HF Doppler systems, ionospheric convection radars at HF, coherent plasma irregularity backscatter/forward scatter radars at VHF and UHF, middle atmosphere VHF radars, mesosphere/lower thermosphere dynamics radars, and large-aperture incoherent scatter radars at VHF and UHF. These systems require careful coordination to avoid interference problems, as return signals can be at thermal noise levels with center frequencies often located in close proximity to other service allocations. Radio Astronomy Service Radio telescopes covering HF to UHF/SHF bands above the ionospheric cutoff (~20 MHz to 2+ GHz) are particularly powerful as solar radio flux monitors and interplanetary space weather monitors of highly geoeffective events such as coronal interaction regions (CIRs) and coronal mass ejections (CMEs). Enumerated in RS.2456-0, systems at these frequencies with space weather applications include the distributed LOFAR stations (Netherlands and several other European countries), the Murchison Widefield Array (western Australia), the Long Wavelength Array (New Mexico and Owens Valley, California), the Japanese interplanetary scintillation system, and dedicated solar radio telescopes / solar flux monitors such as the Nançay radio heliograph in France and the Penticton solar flux monitoring telescopes in Canada. These systems are particularly sensitive to front-end compression from unwanted signals at PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 44

nearby frequencies. The data they provide on calibrated radio flux and frequency dispersion of Type I to Type V solar radio bursts is of fundamental importance to current and future state-of-the-art space weather models. For example, these models have for many decades used the 10.7 cm (2.8 GHz) solar radio flux as a benchmark input parameter. Furthermore, radio emissions of transiting CIR/CME regions can be tomographically analyzed to provide information on interplanetary magnetic field/current dynamics, which are not well specified. These crucially needed parameters are not available from any other ground-based observation. Recommendation: The committee recommends expanded community technical dialogue between space weather sensor maintainers and incumbent service implementers. These coordination efforts are also particularly potent as a future enabler of operational space weather detection, predictions, and warnings that are critical to protection of large national economic sectors and public safety support. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 45

AGENDA ITEM 9.1b: REVIEW OF THE AMATEUR SERVICE AND AMATEUR-SATELLITE SERVICE IN THE FREQUENCY BAND 1240-1300 MHz Agenda Item 9.1b states: “[r]eview of the amateur service and the amateur-satellite service allocations in the frequency band 1 240-1 300 MHz to determine if additional measures are required to ensure protection of the radionavigation-satellite (space-to-Earth) service operating in the same band in accordance with Resolution 774 (WRC-19).” Resolution 774 (WRC-19) considers that the frequency band 1240-1300 MHz is allocated worldwide to the amateur service on a secondary basis and that the frequency band 1240-1300 MHz is important for the amateur community. It also considers that the frequency band 1240-1300 MHz is allocated worldwide and operationally used for radionavigation-satellite service (RNSS) in the space-to-Earth direction. Of primary concern for the science services is the co-primary allocation to EESS (active) at 1215-1300 MHz which is not raised in Resolution 774 (WRC-19). Earth Exploration-Satellite Service Active sensing and reflectometry measurements of Earth are made in channels that overlap with the frequencies under consideration for Agenda Item 9.1b. These measurements are used to study Earth’s deformation due to earthquakes and tectonics as well as groundwater pumping. These measurements are also used for land classification, land-use change detection, surface-soil moisture retrieval, and crops and vegetation monitoring. For example, a current active sensor operating in this frequency range is Japan Aerospace Exploration Agency’s (JAXA’s) PALSAR 1270 MHz (28 MHz bandwidth), which is an all- weather, day-and-night-observing and repeat-pass interferometric instrument used for monitoring natural hazards (e.g., landslides, land surface deformation, land-use change). The recently launched SAOCOM- 1B satellite from the Argentinian CONAE space agency carries an L band synthetic aperture radar operating at about 1275 MHz and will provide complementary coverage to the existing JAXA instrument. Most notably, the forthcoming NASA-ISRO NISAR mission will operate an active instrument with wide- spread global coverage operating at 1257.5 MHz (25 MHz bandwidth). Its data products will be used to support similar natural hazards application as well as monitoring water and carbon changes over global land surfaces. Table 2.7 details these and other sensors observing in this spectral region. Recommendation: The committee recommends that protection from in-band and spurious emissions into overlapping and adjacent EESS allocations be considered when defining allocations for expanded amateur radio within the 1240-1300 MHz frequency band. TABLE 2.7 EESS Sensors Measuring in the 1240-1300 MHz Band Center Frequency Bandwidth Swath Width (Range, if Sensor Satellite (GHz) (MHz) Mode Dependent, km) SAR-L 1A, 1B, 2A, 2B SAOCOM 1.275 up to 80 240 PALSAR-2 JAXA ALOS-2 1.270 up to 80 25-490 PALSAR-3 JAXA ALOS-4 1.270 up to 80 37-700 NISAR NASA/ISRO NISAR 1.215-1.3 up to 80 65-320 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 46

AGENDA ITEM 9.1c: INTERNATIONAL MOBILE TELECOMMUNICATIONS USING FIXED SERVICE ALLOCATIONS Agenda Item 9.1c states as follows: “[s]tudy the use of International Mobile Telecommunication system for fixed wireless broadband in the frequency bands allocated to the fixed services on primary basis, in accordance with Resolution 175 (WRC-19).” Resolution 175 (WRC-19) invites “any necessary studies on the use of IMT systems for fixed wireless broadband in the frequency bands allocated to the fixed service on a primary basis, taking into account the relevant studies, Handbooks, Recommendations and Reports.” Of particular concern for the science services is the inherent difficulty in identifying and remediating sources of radio frequency interference that are mobile. While no frequency bands are specified, the current FS allocations in the international table of frequency allocations include those listed in Table 2.8. The myriad and complex implications of Agenda Item 9.1c are further illustrated by Figure 2.1, which shows that nearly all the EESS and RAS allocations are found either adjacent to or overlapping with allocations to fixed services. TABLE 2.8 List of Primary Fixed Service Allocations that Overlap or Are Adjacent to Science Service Allocations FIXED Allocation Science Services Radio Regulation 13.36-13.41 MHz RAS co-primary RR 5.149 25.21-25.55 MHz RAS adjacent: 25.55-25.67 MHz RR 5.149 29.7-47 MHz ras secondary: 37.5-38.25 MHz RR 5.149 68-74.8 MHz, Regions 1 and 3 RAS in footnote: 73-74.6 MHz in Regions 1 and RR 5.149 3 72-73 MHz, Region 2 RAS adjacent: 73-74.6 MHz, Region 2 74.6-74.8 MHz, Region 2 RAS adjacent: 73-74.6 MHz, Region 2 150.05-156.4875 MHz RAS co-primary: 150.05-153 MHz, Region 1 RR 5.149 RAS co-primary: 150.05-153 MHz, Australia and RR 5.225 India 174-328.6 MHz, Region 3 ras secondary: 225-235 MHz, China only RR 5.250 216-328.6 MHz, Region 2 RAS co-primary: 322-328.6 MHz, all Regions RR 5.149 230-328.6 MHz, Region 1 406.1-430 MHz RAS co-primary: 406.1-410 MHz RR 5.149 470-890 MHz RAS co-primary: 608-614 MHz, Region 2 and RR 5.307 India RAS co-primary: 606-614 MHz, in the African RR 5.149, RR 5.304, Broadcasting Area and China RR 5.305 ras secondary: 608-614 MHz in Region 1, except RR 5.149, RR 5.306 for African Broadcasting Area, and Region 3 1350-1400 MHz RAS in footnote: 1330-1400 MHz RR 5.149 eess/srs secondary: 1370-1400 MHz RR 5.339 RAS/EESS/SRS adjacent: 1400-1427 MHz RR 5.340 1427-1525 MHz RAS/EESS/SRS adjacent: 1400-1427 MHz RR 5.340 1668.4-1690 MHz RAS co-primary: 1668.4-1670 MHz RR 5.149 RAS adjacent: 1660-1668.4 MHz RR 5.149 1700-2690 MHz ras secondary: 1718.8-1722.2 MHz RR 5.149, RR 5.385 eess/srs secondary: 2640-2690 MHz RR 5.339 ras secondary: 2655-2690 MHz RR 5.149 RAS/EESS/SRS adjacent: 2690-2700 MHz RR 5.340 3300-4200 MHz RAS in footnote: 3332.0-3339.0 MHz RR 5.149 RAS in footnote: 3345.8-3352.5 MHz RR 5.149 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 47

4400-5000 MHz ras secondary: 4800-4990 MHz RAS co-primary: 4825-4835 MHz and 4950- RR 5.149, RR 5.443 4990 MHz in Argentina, Australia, and Canada RAS in footnote: 4825-4835 MHz RR 5.149 RAS in footnote: 4950-4990 MHz RR 5.149 eess/srs secondary: 4950–4990 MHz RR 5.339 RAS co-primary 4990-5000 MHz RR 5.149 5850-8500 MHz RAS in footnote: 6650-6675.2 MHz RR 5.149, RR 5.458A EESS in footnote: 6425-7075 MHz and 7075- RR 5.458 7250 MHz 10.0-10.45 GHz, Regions 1 and 3 EESS(active) co-primary: 10.0-10.4 GHz RR 5.474A, 5.474B, 5.575C 10.5-10.68 GHz RAS/EESS co-primary: 10.6-10.68 GHz RR 5.149, RR 5.482A RAS/EESS/SRS adjacent: 10.68-10.7 GHz RR 5.340, RR 5.483 10.68-10.7 GHz, RR 5.483 RAS/EESS/SRS co-primary: 10.68-10.7 GHz RR 5.340 10.7-11.7 GHz RAS/EESS/SRS adjacent: 10.68-10.7 GHz RR 5.340, RR 5.483 12.75-13.25 GHz EESS(active) adjacent: 13.25-13.75 GHz RR 5.498A, RR 5.501B 14.4-15.35 GHz ras secondary: 14.47-14.5 GHz RR 5.149 eess secondary: 15.2-15.35 GHz RR 5.339 RAS/EESS/SRS adjacent: 15.35-15.4 GHz RR 5.340 17.7-19.7 GHz EESS(passive) co-primary: 18.6-18.8 GHz 21.2-23.6 GHz EESS(passive) co-primary: 21.2-21.4 GHz RAS in footnote: 22.01-22.21 GHz RR 5.149 RAS/EESS(passive) co-primary: 22.21-22.5 GHz RR 5.149, RR 5.532 RAS in footnote: 22.81-22.85 RR 5.149 RAS in footnote: 23.07-23.12 GHz RR 5.149 RAS/EESS/SRS adjacent: 23.6-24.0 GHz RR 5.340 31.0-31.3 GHz RAS in footnote: 31.2-31.3 GHz RR 5.149 RAS/EESS/SRS adjacent: 31.3-31.5 GHz RR 5.340 31.8-33.4 GHz RAS/EESS/SRS adjacent: 31.5-31.8 GHz RR 5.340 Region 2 RR 5.149 Reg 1 & 3 36.0-43.5 GHz EESS(passive) co-primary: 36-37 GHz RR 5.149 RAS co-primary: 42.5-43.5 GHz RR 5.149 47.2-50.2 GHz RAS co-primary: 48.94-49.04 GHz RR 5.340, RR 5.555 EESS(passive) adjacent: 50.2-50.4 GHz RR 5.340 50.4-52.6 GHz RAS on a nation by nation basis: 51.4-54.25 RR 5.556 EESS(passive) adjacent: 50.2-50.4 GHz RR 5.340 EESS(passive) adjacent: 52.6-54.25 GHz RR 5.340 55.78-66 GHz EESS(passive) co-primary: 55.78-59.3 GHz RR 5.557A RAS on a nation by nation basis: 58.2-59, 64-65 RR 5.556 GHz 71-76 GHz RAS adjacent: 76-77.5 GHz RR 5.149 81-86 GHz RAS co-primary: 81-86 GHz RR 5.149 RAS adjacent: 79-81 GHz RR 5.149 RAS/EESS/SRS adjacent: 86-92 GHz RR 5.340 92-94 GHz RAS co-primary: 92-94 GHz RR 5.149 RAS/EESS/SRS adjacent: 86-92 GHz RR 5.340 94.1-100 GHz RAS co-primary: 94.1-100 GHz RR 5.149 RAS/EESS/SRS adjacent: 100-102 GHz RR 5.340 102-109.5 GHz RAS co-primary: 102-109.5 GHz RR 5.149 RAS/EESS/SRS adjacent: 100-102 GHz RR 5.340 RAS/EESS/SRS adjacent: 109.5-111.8 GHz RR 5.340 111.8-114.25 GHz RAS co-primary: 111.8-114.25 GHz RR 5.149 RAS/EESS/SRS adjacent: 109.5-111.8 GHz RR 5.340 RAS/EESS/SRS adjacent: 114.25-116 GHz RR 5.340 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 48

122.25-123 GHz EESS(passive) adjacent: 119.95-122.25 GHz 130-134 GHz RAS co-primary: 130-134 GHz RR 5.149, RR 5.562A EESS(active) co-primary: 133.5-134 GHz RR 5.562E 141-148.5 GHz RAS co-primary: 141-148.5 GHz RR 5.149 RAS adjacent: 136-141 GHz RR 5.149 RAS/EESS/SRS adjacent: 148.5-151.5 GHz RR 5.340 151.5-164 GHz RAS co-primary: 151.5-158.5 GHz RR 5.149 RAS/EESS/SRS adjacent: 148.5-151.5 GHz RR 5.340 RAS/EESS/SRS adjacent: 164-167 GHz RR 5.340 167-174.5 GHz RAS in footnote: 168.59-168.93 GHz, 171.11- RR 5.149 171.45 GHz, 172.31-172.65 GHz, 173.52-173.85 GHz RAS co-primary in Korea (Rep. of): 171-171.6, RR 5.562D 172-172.8, 173.3-174 GHz RAS/EESS/SRS adjacent: 164-167 GHz RR 5.340 174.5-174.8 GHz EESS(passive) adjacent: 174.8-182 GHz 191.8-200 GHz RAS in footnote: 195.75-196.15 GHz RR 5.149 EESS(passive) adjacent: 190-191.8 GHz RR 5.340 RAS/EESS/SRS adjacent: 200-209 GHz RR 5.340 209-226 GHz RAS co-primary: 209-226 GHz RR 5.149 RAS/EESS/SRS adjacent: 200-209 GHz RR 5.340 RAS/EESS/SRS adjacent: 226-231.5 GHz RR 5.340 231.5-235 GHz RAS/EESS/SRS adjacent: 226-231.5 GHz RR 5.340 EESS(passive) adjacent: 235-238 GHz 238-241 GHz EESS(passive) adjacent: 235-238 GHz RAS adjacent: 241-248 GHz RR 5.149 252-275 GHz RAS co-primary: 252-275 GHz RR 5.149 RAS/EESS/SRS adjacent: 250-252 GHz RR 5.340 NOTE: Science Services written in all uppercase letters denote primary/co-primary allocations. Science Services written in all lowercase letters denote secondary allocations. Acronyms are defined in Appendix B. Radio Astronomy Service Since it is often possible to coordinate and utilize geographic shielding to protect radio astronomy facilities from services that are inherently stationary, a large fraction of the allocations to fixed services include co-primary allocations to the radio astronomy service. However, the same is not true regarding mobile services, as moving transmitters may result in intermittent interference that is difficult to trace and mitigate. Thus, consideration of the co-primary and adjacent allocations relevant to Agenda Item 9.1c are critical to retain the viability of scientific use of the radio spectrum. For example, as discussed regarding WRC-23 Agenda Item 1.4, the 470-890 MHz band includes co-primary allocations to radio astronomy in the 606-614 MHz spectral band, with slight variations in spectrum allocations in some countries. In the United States, the 608-614 MHz band is listed in US246, where it is noted that for this frequency band no station, except for medical telemetry equipment, is authorized to transmit. Thus, while allocated to the land mobile service in the United States, this frequency band is not compatible with a global allocation to international mobile telecommunications. Similar analysis and considerations must be applied to any future change in spectrum allocations. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 49

FIGURE 2.1 Comparing the distribution of primary allocations to Fixed Services (blue), Earth Exploration-Satellite Services (passive) (orange), and Radio Astronomy Services (green) in the International Table of Frequency Allocations, along with bands having RR 5.340 “All emissions prohibited” protection (red). RAS and EESS allocations include RR 5.149, RR 5.458, and RR 5.556. Earth Exploration-Satellite Service In contrast with RAS, EESS observations are not confined to limited areas of the globe. Indeed, it is the ability of EESS sensors to observe worldwide that makes them such key resources in the study of the Earth system. Accordingly, in cases where emission from Fixed Services contaminates the EESS signals, the only recourse is to excise the affected observations from the data record. As undesirable as this circumstance is, it is vastly preferable to cases where contaminating emitters become mobile, and, as Agenda Item 9.1c seems to be seeking to consider, far more numerous and widespread. The true value of EESS measurements is their ability to track changes in the Earth system. Timescales for these changes range from hourly (e.g., for weather), through seasonal (e.g., for agriculture), to decadal (for studies of climate). A continually changing background of interference in these measurements has the potential to dramatically undermine their value. While data losses associated with strong individual fixed emissions are highly regrettable, they are, in many cases at least, readily identifiable, and their impact somewhat predictable and stationary in time. A change in the interference landscape to one of more widespread, patchy, and continually moving lower-level emissions would arguably render the task of identifying cases of interference intractable, seriously compromising the value of the entire record. Further, the EESS observations, particularly those from EESS (passive), operate as a system, having different widely spread bands that provide complementary but still overlapping information on PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 50

surface properties and atmospheric structure over a range of altitudes. The complete picture can only be obtained when emissions in each band are considered as a whole. Accordingly, even if only one frequency band suffers from interference in any given spatial and temporal location (pixel), the value of the entire pixel is compromised. For example, information on a range of Earth surface and ocean surface parameters including soil moisture, surface freeze/thaw state, sea-surface temperature and salinity, and sea-ice cover derive from various combinations of EESS (passive) measurements in allocated bands at 1.4, 6, 10, 18, 23, 31, 37, and 89 GHz, all of which are affected by this agenda item in that they overlap or are adjacent to primary fixed allocations that are under consideration for allocation to IMT. Recommendation: Careful study of the potential for radio frequency interference into shared and adjacent bands allocated to the passive scientific services should be completed before consideration of International Mobile Telecommunications use of fixed service allocations. Specifically, in contrast with fixed services, tracing radio frequency interference caused by mobile applications is difficult due to their transitory nature. Thus, sharing studies must include not only consideration of aggregate interference, but also the requirements for robust geolocation information and geolocation tracking that are necessary to enforce geographic restrictions and other effective spectrum-sharing techniques. Further, in the advent of future allocations to the mobile service in these broad frequency bands, the committee believes that the most effective protection would be through primary allocations to the RAS for all of the relatively small bands designated in RR 5.149 that could be impacted negatively by such allocations through aggregate interference from in-band, out-of-band, and spurious emissions. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 51

AGENDA ITEM 9.1d: PROTECTION OF EESS FROM NON-GSO FSS Agenda Item 9.1d considers “protection of EESS (passive) in the frequency band 36-37 GHz from non-GSO FSS space stations.” The 36-37 GHz band is allocated to the EESS (passive) on a co-primary basis with Fixed, Mobile, and SRS (passive). Although RAS does not have an allocation in this band, the narrow frequency range 36.43-36.5 GHz is listed in RR 5.149, where administrations are urged to take all practicable steps to protect the RAS. RR 5.550A states “[f]or sharing of the band 36-37 GHz between the Earth exploration- satellite (passive) service and the fixed and mobile services, Resolution 752 (WRC-07) shall apply.” Tables 2 and 3 of Annex 1 to Resolution 752 (WRC-07) provide sharing criteria for fixed and mobile services, respectively, with maximum power at the transmitter port of −10 dBW for most applications and −5 dBW for hub stations in point-to-multipoint systems. Recommendation ITU-R RS.2017 lists a maximum interference level of −166 dBW for a 100 MHz bandwidth at 36-37 GHz, with a limit of 0.1 % that this might be exceeded in area or time. While the 36-37 GHz band is co-primary with Fixed and Mobile services, this co-existence has been benign in the past largely due to the absence of active use of this band. Any widespread communication use of these frequencies will dramatically change this situation. Earth Exploration-Satellite Service The 36-37 GHz band is critical for satellite passive microwave measurements primarily of precipitation and sea ice. This band is the most widely used passive microwave channel between the 22 GHz water vapor line and the 60 GHz oxygen line complex, providing unmatched radiometric sensitivity to key Earth system variables. Measurements in this band are used, in conjunction with those from other bands, in a wide variety of environmental products such as measurements of atmospheric temperature and water vapor, precipitation, cloud properties such as cloud liquid water, surface freeze-thaw conditions and snow cover, sea-ice concentration, oil slicks, sea-surface temperature, and ocean vector winds. Current missions with passive receivers at or near 36-37 GHz are listed in Table 2.9. In addition, the DoD Microwave Imager (MWI) planned for late 2023 and the European Copernicus Imaging Microwave Radiometer (CIMR; planned for 2027) have channels near 36.5 to 37.75 GHz that will be used for observations of sea-ice concentration, sea-surface temperature, total atmospheric water vapor, total cloud liquid water vapor, precipitation, snow water equivalent and snow depth. The EESS systems operate in a direct detection mode, and the signal being emitted from Earth’s surface and atmosphere is very weak, resulting in the need to average over space and time to retrieve a useful measurement. Anthropogenic energy leaking into this band has the strong potential to overwhelm the signal being sensed, rendering the measurements unusable for the purposes they were intended. Thus, any out of band emissions (OOBE) from non-GSO downlinks operating at 37.5-38 GHz have the potential to compromise measurements made at this frequency. There are multiple routes by which out-of-band emissions from 37.5-38 GHz non-GSO stations can interfere with 36-37 GHz EESS (passive) observations. First, non-GSO signals reflected off Earth’s surface (particularly from highly reflective surfaces such as salt water and ice) can be directed into an EESS (passive) beam, corrupting the measurements. Second, depending on the geometry, emissions from the non-GSO station has the potential to couple directly into the EESS (passive) beam. In the case where the non-GSO emitter lies below the EESS (passive) sensor, some attenuation may result from the fact that the non-GSO emissions are largely targeted in a downwards direction. However, a significant concern arises from another geometry—EESS (passive) sensors are self-calibrating, making frequent views of cold-space (typically an “upwards looking” beam) to establish a zero-level baseline signal. Cases where a non-GSO sensor overflies an EESS (passive) satellite during one of these upward-looking calibration PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 52

views have the potential to affect multiple prior and subsequent observations. An additional concern for the direct-beam coupling cases is the unlikely, but highly consequential, possibility of permanent damage being done to EESS (passive) sensors should an emitting non-GSO station pass close to the EESS (passive) spacecraft. As noted above, non-GSO signals reflected off Earth’s surface contribute additively to aggregate surface emissions. As an example of the potential risk into the EESS (passive) 36-37 GHz channel, consider the case of the GPM Microwave Imager (GMI) radiometer and current regulations regarding out- of-band emissions from mobile devices. The GMI radiometer views the ground with a 48.5° scan angle. Out-of-band emission limits for IMT stations transmitting at 37-40.5 GHz are −23 dB(W/GHz) within the frequency band 36-37 GHz (Resolution 243 (WRC-19)). In the case where an element of a patch antenna within the base station (assumed to have 8 dBi gain) is pointing at GMI, the free-space loss due to the distance between transmitter and receiver (403 km altitude) is 179.7 dB. Given losses due to atmospheric absorption (0.98 dB assumed), the fact that GMI observes individual polarizations (a 3 dB reduction in each channel), and that the GMI antenna gain is 43 dBi in this band, the Resolution 243 OOBE limits would result in a GMI-received power of −165.6 dB(W/100 MHz) from a single IMT base station in the beam. Accordingly, a single IMT base station in the GMI main beam with these out-of-band emission levels will cause an interference signal 0.5 dB above the Recommendation ITU-R RS.2017 criteria. Given that the GMI footprint is several hundred square kilometers, the potential for a large number of base stations in the footprint is high, with the corresponding concern that the aggregate out-of-band emissions from IMT base stations alone will exceed the maximum interference criteria. With additional applications, such as those proposed here, the potential for irreparable contamination of the 36-37 GHz EESS channel will continue to increase. TABLE 2.9 EESS (Passive) Satellite Missions with Receivers Close to the Frequency Band 36-37 GHz Center Frequency (GHz) and Bandwidth IFOVb a Sensor Satellite Polarization (MHz) (km) AMSR2 JAXA GCOM-W1 36.5 V,H 1000 10 × 10 GMI NASA GPM 36.5 V,H 700 13 × 22 WindSat DoD Coriolis 37.0 V,H,3,4 2000 6.25 × 12.5 AMR/AMR-C NOAA JASON-2/3 and 34.0 V (nominal, 700 25 JASON- CS-A/B with H backup) MTVZA-GY RosHydroMet Meteor-M 36.7 V,H 400 30 × 67 MWRI CMA FY-3C/D 36.5 V,H 400 18 × 30 MWRI NSOAS HY-2A + 37.0 V,H 1000 15 × 22 MWR Copernicus Sentinel-3 36.5 Linear 1000 30 SSM/I DoD DMSP-F15 37.0 V,H 1000 24 × 36 SSMIS DoD DMSP-F16 to F-19 37.0 V, H 400 27.5 × 44.2 MWI DoD WSF-M 36.5-36.75 V,H,3,4 500 10 × 16 MWI DoD WSF-M 37.0-37.75 V,H 2500 10 × 16 CIMR Copernicus 36.5 V,H,3,4 1000 ≤5 (goal 4) AMSR3 JAXA GOSAT-GW 36.5 V,H 1000 10 × 10 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Polarization codes are H-horizontal, V-vertical, 3 and 4-3rd and 4th components of the Stokes vector. b Instantaneous field-of-view dimensions. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 53

Recommendation: The committee recommends that studies of sharing between EESS (passive) at 36-37 GHz and non-geostationary orbit (GSO) emissions at 37.5-38 GHz are guided by the requirements defined in ITU-R RS.2017. These studies should explicitly consider aggregate emissions from a large number of orbiting non-GSO emitters, consistent with the size of the constellations being developed in other bands, in addition to existing and planned ground-based sources. Studies should consider interference from signals reflected off Earth’s surface, and those coupling directly into both the Earth-viewing and cold-sky calibration beams of the EESS (passive) sensor. Attention should also be paid to the potential for permanent damage to EESS (passive) sensors should emitting non-GSO satellites pass close to an EESS (passive) platform. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 54

WRC-27 AGENDA ITEM 2.1: THE RADIOLOCATION SERVICE AT 231.5-275 GHz AND 275-700 GHz WRC-27 Agenda Item 2.1 considers “in accordance with Resolution 663 (WRC-19), additional spectrum allocations to the radiolocation service on a co-primary basis in the frequency band 231.5-275 GHz and an identification for radiolocation applications in frequency bands in the frequency range 275- 700 GHz for millimetre and sub-millimetre wave imaging systems.” Agenda Item 2.1, and the resolution it cites, invites future study of prospects for sharing between active millimeter and submillimeter-wave imaging systems and other services, both in the 231.5-275 GHz band and at frequencies above 275 GHz (where no international frequency allocations exist currently), up to 700 GHz. There are existing primary allocations to EESS (passive) at 235-238 GHz and to both EESS (passive) and RAS at 250-252 GHz, the latter receiving RR 5.340 (“All emissions prohibited”) protection. In addition to the exclusively passive 250-252 GHz band, RAS has co-primary allocations at 241-248 GHz and 252-275 GHz and a secondary allocation at 248-250 GHz. The frequency bands 241-250 GHz and 252-275 GHz are listed in RR 5.149, where administrations are urged to take all practicable steps to protect radio astronomy from harmful interference. The main application of EESS (passive) observations at these frequencies is in atmospheric science, specifically atmospheric chemistry and studies of cloud ice particles. An additional allocation to EESS within this frequency band is under consideration during WRC-23 (Agenda Item 1.14). As listed in Recommendation ITU-R RA.769, the threshold levels of harmful interference for RAS at these frequency ranges is approximately −217 dBW/(m2 Hz) for continuum observations. As listed in Recommendation ITU-R RS.2017, the threshold levels of harmful interference for EESS (passive) at these frequency bands is −194 dBW in a 3 MHz bandwidth. The bands above 275 GHz are not currently allocated. While several regions between 275 GHz and 1000 GHz have been identified for use by administrations for passive service applications, these identifications do not preclude the use of these bands by active services, although the latter are urged to take all practicable steps to protect the identified passive services from harmful interference, pending more specific allocations at some future date (RR 5.565). For EESS (passive), as listed in Recommendation ITU-R RS.2017, at these frequency bands, the maximum levels for interference depend on the operational modes and are −194 dBW for a 3 MHz reference bandwidth for microwave limb sounding applications and range from −160 to −155 dBW for a 200 MHz bandwidth for nadir or conical scanning modes. The ITU-R Report RA.2189-1 includes tables that list threshold levels for interference to the RAS above 275 GHz, which vary from −215 dBW/(m2 Hz) to −195 dBW/(m2 Hz) for continuum observations within this frequency range. Earth Exploration-Satellite Service In atmospheric chemistry, these spectral regions are targeted by existing and planned instruments tracking the recovery of Earth’s fragile ozone layer in response to the Montreal protocol to ban the production of ozone-depleting substances. The trace gases to be measured are very tenuous. For example, chlorine monoxide (ClO, a key agent in the chemical destruction of ozone) has peak abundances of only ~3 parts per billion molecules in the stratosphere. Long path-lengths through the atmosphere and highly sensitive instruments are needed to observe such species, dictating that measurements be made in a limb- sounding geometry. The key chlorine activation reactions that give rise to the “ozone hole” occur on the surfaces of cloud particles. Submillimeter-wave signals are unaffected by such clouds, and their detection is critical because limb-sounding instruments in the infrared and ultraviolet have difficulty measuring trace gas abundances in the presence of cloud emissions and scattering. A wealth of different trace gas species can be measured by such instruments. Many, notably ozone (O3), nitric acid (HNO3), and sulfur dioxide (SO2), have many relatively strong lines spread throughout the spectrum. Other key species, PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 55

notably water vapor (the strongest greenhouse gas) and carbon monoxide (the most widely used tracer of pollution emissions and transport of polluted air) have lines spaced relatively sparingly in the submillimeter spectrum, making the regions around these lines particularly attractive for current and future planned instruments. Broadening of spectral lines by molecular collisions dictates that bandwidths of order 1 MHz must be used to capture the full line shape and deduce the atmospheric composition profiles. More recently, the potential of this spectral region to provide unique information on cloud ice particles in the middle and upper troposphere (~5 km and above) is gaining attention, and plans are under way to exploit this information. Such ice clouds are an important and poorly understood aspect of the atmosphere system and represent a significant uncertainty on climate projections. A spaceborne sensor under development will provide measurements of ice cloud signatures in this spectral region. Importantly, such measurements do not employ limb-viewing, instead favoring conical and/or cross-track scanning. This increases the likelihood of observations down to the surface, making RFI a potentially much greater impediment to such observations. Further, in contrast with gas-phase chemistry observations, clouds are far more spatially heterogeneous, presenting a challenge to any techniques used to excise RFI- contaminated scenes based on assumptions that RFI sources would be localized. Furthermore, the committee notes that interest has been expressed in using measurements from the strong 380 GHz water vapor line for remote sounding of water vapor in particularly arid regions such as in mountainous and/or polar areas (e.g., ITU-R RS.2194). Finally, some concepts for future geostationary microwave sounders have included channels in the 325, 380, and 425 GHz regions. Table 2.10 lists instruments (current or planned) making observations in these regions. TABLE 2.10 List of Instruments Measuring in 231-700 GHz Instrument Bands Status Aura MLS 115-122, 177-184, 199-207, In orbit 229-237, 242-250, 624-626, 632-637, 648-654, 659-662, 2501-2545 GHz Odin SMR 118.25-119.25, 486.1-503.0, In orbit. 541.0-558.0, 547.0-581.4 GHz ICI 239.5-247, 314-335, 439-456, In development 657-670 GHz TWICE 320, 380, ~600, ~800 GHz In early-stage development Continuity-MLS 322–358, 622–658 GHz In early-stage development NOTE: Measurements in italics, while outside the 231-700 GHz range, are included for completeness. Acronyms are defined in Appendix B. Radio Astronomy Service The frequency range between 231.5-700 GHz is heavily used for radio astronomy observations of numerous molecular line transitions, which has resulted in major advances in the nascent field of astrochemistry. Because of high atmospheric absorption due to water vapor, ground-based observations at these frequencies can only be made from high and arid sites, in spectral windows bounded by strong water lines. Radio observatories that observe in atmospheric windows across the considered frequency range are listed in Table 2.11. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 56

TABLE 2.11 RAS Facilities Operating from 231.5-700 GHz Max. Obs. Frequency Latitude Longitude Altitude Facility (GHz) Location (deg N) (deg E) (m) Arizona Radio Observatory Kitt Peak 275 Arizona, 32.0 –111.6 1895 12m Telescope (ARO KP12m) USA Arizona Radio Observatory 720 Arizona, 32.7 –109.9 3160 Submillimeter Telescope (ARO SMT) USA Atacama Large 950 Chile –23.0 –67.8 5075 Millimeter/submillimeter Array (ALMA) Atacama Pathfinder Experiment 738 Chile –23.0 –67.8 5105 (APEX) Greenland Telescope (GLT) 373 Greenland 76.5 –68.7 90 IRAM 30–meter 375 Spain 37.1 –3.4 2920 James Clerk Maxwell Telescope 700 Hawaii, USA 19.8 –155.5 4120 (JCMT) Large Millimeter Telescope (LMT) 275 Mexico 19.0 –97.3 4595 NANTEN2 880 Chile –23.0 –67.7 4800 Northern Extended Millimeter Array 370 France 44.6 5.9 2620 (NOEMA) Submillimeter Array (SMA) 420 Hawaii, USA 19.8 –155.5 4115 South Pole Telescope 350 Antarctica –90.0 0 2816 NOTE: Acronyms are defined in Appendix B. RAS uses these frequencies to pursue a number of key science goals. Many of the most common interstellar molecules have rotational transitions in this range that serve as important probes. These molecules include CO, HCN, HCO+, H2O, CS, and OH, which trace the structure of galaxies, the properties of super-massive black holes, characteristics of star-forming regions, stages of stellar evolution, and the building blocks of interstellar chemistry. Recently, observations at 230 GHz utilizing submillimeter-wave radio telescopes located around the world produced the first image of a black hole; similar observations at higher frequencies will provide even higher spatial resolution and insights into the structure and evolution of black holes. This frequency range is also essential for continuum observations of emission from dust throughout the universe. This spectral region is also important for the study of life in the universe. The carbon on Earth today had to come from exogenous delivery via comets, meteorites, and interplanetary dust particles, which appear to carry debris from the original molecular cloud in which the solar system was created. Observations of organic molecules in molecular clouds are enabling the link to be made between the carbon inventory on planets and that of the pre-solar nebula. In addition to the observatories in Table 2.11, a number of cosmic microwave background (CMB) experiments map the structure of the CMB in multiple millimeter-wave bands. These include the South Pole Telescope (SPT) and BICEP-Keck experiment at the South Pole; and the Atacama Cosmology Telescope (ACT), Cosmology Large Angular Scale Surveyor (CLASS), and POLARBEAR in northern Chile. Bands used in current CMB observations include one approximately 50 GHz-wide centered at 220 GHz, and plans are in place to add a similar wide band centered at 270 GHz across these facilities. These experiments utilize this very wide bandwidth, along with careful design of modulation and observing PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 57

strategies, to target nanoKelvin sensitivity levels. They provide a window into the early universe and into physics at energy scales orders of magnitude beyond the limits of Earth-bound particle accelerators. Moreover, because these experiments observe large amounts of sky at high temporal cadence, they are also yielding new insights into the time-dependent millimeter-wave universe. CMB observations are poised to realize an order-of-magnitude improvement in sensitivity in the coming decade and must remain protected from harmful interference. Recommendation: The committee recommends that in defining allocations for active services below 275 GHz the current protections for RAS and EESS (passive) be adhered to, with attention paid to out-of-band and spurious emissions, ensuring that they do not exceed the limits specified in Recommendations ITU-R RA.769 and ITU-R RS-2017. Further, the committee recommends that above 275 GHz, Administrations continue to take all practicable steps to avoid harmful impacts to identified passive services. These steps should include efforts to avoid allocations to active services in spectral regions where atmospheric opacity is minimal, as these frequency bands are most useful for both RAS and EESS (passive). When spectral protection is not feasible, dynamic frequency allocation and geofencing should be used to protect the science services. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 58

WRC-27 AGENDA ITEMS 2.2 and 2.3: Ka-BAND and V-BAND Proposed WRC-27 Agenda Items 2.2 and 2.3 include consideration of frequency allocations in Ka band (27-40 GHz) and V band (40-75 GHz). Specifically, WRC-27 Agenda Item 2.2 considers “use of the frequency bands 37.5-39.5 GHz (space-to-Earth), 40.5-42.5 GHz (space-to-Earth), 47.2-50.2 GHz (Earth- to-space), and 50.4-51.4 GHz (Earth-to-space) by aeronautical and maritime Earth stations in motion with geostationary space stations in the fixed satellite service,” while WRC-27 Agenda Item 2.3 considers “studies relating to spectrum needs and possible allocations of the frequency band 43.5-45.5 GHz to the fixed-satellite service.” Earth Exploration-Satellite Service Recommendation ITU-R-RS.2017 defines interference criteria for all EESS passive satellites as −166 dBW for 100 MHz bandwidth at 36-37 GHz, −166 dBW for 200 MHz bandwidth at 50.2-50.4 GHz, and −169 dBW for 100 MHz bandwidth at 52.6-59.3 GHz. For these bands, the committee remains consistent with its views for WRC-19 Agenda Item 1.13. 4 In particular, consideration of OOBE is particularly important for Earth stations in motion (ESIM) to GSO space station communication use in bands that are proposed adjacent to passive Earth remote sensing bands. It is therefore imperative that any proposed band use must include adequate spectral separation (guard bands) to protect the incumbent users of the passive bands from the aggregate OOBE interference of many ESIMs within the footprint of the EESS sensor. These incumbent EESS missions represent billions of dollars in development and deployment of instruments and satellites and were designed and developed with no expectation that mobile communications would be in such close spectral proximity. Incumbent passive EESS users at these frequencies (e.g., 37 GHz) operate in a direct detection (homodyne) mode with limited protection against OOBE. In direct detection, band definition is achieved with filters that are limited by the filter technology. For a given technology, the bandwidth of a filter is proportional to the central frequency, so the width of the necessary guard bands to suppress emissions to a desired level also increases in proportion to the frequency. In other words, proportionally larger guard bandwidths are needed as the frequency increases. Furthermore, for the same reasons, it is unclear whether ESIM mobile devices with limited size and cost will be able to adequately filter their OOBE to meet the stringent requirements of the adjacent passive bands. Creating guard bands proportional to the operating frequency, that also factor in bandwidth use by incumbent EESS applications, is therefore the best way to protect vital global weather forecasting and climate research. Passive satellite missions operating in the bands in question are enumerated in Table 2.12. 37.5-39.5 GHz Band The primary EESS allocation at 36-37 GHz—in close proximity to the 37.5-39.5 GHz band under discussion for ESIM/GSO applications—is widely used in Earth remote sensing. It offers the largest contiguous bandwidth for passive observations in the region of the spectrum spanning from the 22 GHz water line to the 60 GHz oxygen absorption band. The high sensitivity that ensues from this broad bandwidth makes measurements in this band key to many scientific applications, including atmospheric water vapor, precipitation, cloud properties, surface freeze/thaw conditions, snow, sea ice, sea-surface 4 National Academies of Sciences, Engineering, and Medicine. 2017. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items of Interest to the Science Services at the World Radiocommunication Conference 2019. Washington, DC: The National Academies Press. https://doi.org/10.17226/24899. pp. 31-40. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 59

TABLE 2.12 EESS (Passive) Satellite Missions Relevant to WRC-27 Agenda Items 2.2 and 2.3a,b Relevant Center Bandwidth Sensor Satellite Frequency (GHz) (MHz) AMSR2 GCOM-W1 36.5 1000 AMSU-A, ATMS NOAA-15, NOAA-18, NOAA-19, 50.3, 51.76 180, 400 NOAA-20; NOAA JPSS-2, JPSS-3; EUMETSAT MetOp-A, MetOp-B; NOAA Suomi NPP GMI NASA GPM 36.5 1000 a WindSat DoD Coriolis 37 2000 MWI EUMETSAT MetOp-SG 50.3 400 MTVZA-GY RosHydroMet Meteor-M, Meteor-M2 48 400 MWRI CMA FY-3B, FY-3C, FY-3D, FY-3E, 36.5 1000 FY-3F, FY-3G MWRI NSOAS HY-2A, HY-2B 37 1000 a b SSM/I, SSMIS DoD DMSP F-15, 16, 17, 18 37, 50.3 1600, 380 CIMR Copernicus 36.5 1000 MWI DoD WSF-M 35.5-36.75, 37.0- 500, 2500 37.75 AMSR3 JAXA GOSAT-GW 36.5 1000 NOTE: Text in italics denotes missions in development. Acronyms are defined in Appendix B. a Department of Defense satellites operate outside the passive protected band and into a shared government use band. b Not every instrument in the list has every channel. SSMIS has the full channel suite. temperature, and ocean vector winds. 5 Missions that provide measurements in this band include the NASA Global Precipitation Measurement Mission’s Global Microwave Imager, the Department of Defense (DOD) Special Sensor Microwave/Imager and WindSat instruments, and the Japan Aerospace Exploration Agency (JAXA) Global Change Observation Mission-Water 1’s Advanced Microwave Scanning Radiometer 2. As many of these sensors operate in direct detection mode, their ability to mask OOBEs is limited by basic physics. A particular concern for the proposed ESIM/GSO transmitters is that they will offer very limited protection for these EESS instruments, as the bandwidth of the sensors in these allocated passive bands is near to or even overlaps the 37.5 GHz lower band edge. Given their low orbits and large receiver antennas, such EESS passive sensors are particularly susceptible to terrestrial interference. In cases where multiple interfering sources are in the beam, assuming the sources are incoherent, the interfering powers received by the EESS (passive) sensor add directly. For example, with 1,000 interfering ESIM sources of equal strength within a sensor footprint, the interference level is raised by 30 dB over that of a single source. This level of interference mandates that OOBE filtering levels of >36 dB 6 and >66 dB rejection be adopted for a single mobile device and 1,000 5 See, for example, NASA, “Global Precipitation Mission,” last updated August 3, 2017, http://www.nasa.gov/mission_pages/GPM/spacecraft/; NASA, “TMI,” http://pmm.nasa.gov/node/161; Jet Propulsion Laboratory, “SSM/I,” http://podaac.jpl.nasa.gov/ SSMI; and NOAA, “Sensors—WindSat Overview,” https://www.star.nesdis.noaa.gov/mirs/windsat.php. 6 National Academies of Sciences, Engineering, and Medicine. 2017. Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items of Interest to the Science Services at the World PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 60

mobile devices, respectively. The challenges associated with implementing such filtering suggest that it would be prudent to include spectral separation (guard bands), designed to match the incumbent users’ filter response. Such safeguards are critical for preserving these expensive and important observational assets. Alternatively, dynamic allocation of frequencies could be required, such that emissions in critical bands are halted when EESS (passive) sensors are observing the location of a given transmitter. 50.4-51.4 GHz Band The proposed ESIM/GSO services in the 50.4-51.4 GHz band are directly adjacent to the critical 50.2-50.4 EESS (passive) band used for remote sounding of atmospheric temperature profiles. Despite this passive band being subject to RR 5.340 “all emissions prohibited” protection, no guard band is included between it and the proposed allocations. Further, given the ESIM/GSO proposed allocation at 47.2-50.2 GHz, the EESS (passive) 50.2-50.4 GHz band is set to be surrounded on both sides by active users. This band is heavily used by weather satellites from multiple countries and agencies (see Table 2.12). Being in the wings of the 60 GHz oxygen band, this band provides unique vertically resolved measurements of atmospheric temperature. Such measurements are central to weather forecasting, particularly to the forecasting of extreme weather events that have large impacts on human life and safety and on regional economies. The ability of this band to sound down to Earth’s surface makes their measurements particularly susceptible to RFI, mandating strong protections. Guard bands, both below and above this band, are an essential component of such protection. Definition of guard-band characteristics must take into account the technological limitations of both incumbent receivers and proposed ESIM/GSO transmitters. Radio Astronomy Service Of particular concern for radio astronomy are the frequency bands at 42.5-43.5 GHz and 48.94-49.04 GHz, which are at risk from adjacent and in-band transmissions, respectively. As noted in RR 5.149, radio astronomy is particularly vulnerable to spaceborne radio interference because terrain shielding cannot be utilized to block transmissions originating at high altitude. The detrimental levels for continuum and spectral line radio astronomy observations are −227 dBW/(m2 Hz) and −210 dBW/(m2 Hz) for the average across the full 1 GHz band and the peak level in any single 500 kHz channel (Recommendation ITU-R RA.769, Tables 1 and 2, respectively). Internationally, the following major telescopes have receivers that operate in these frequency bands: Very Large Array (U.S.), Very Long Baseline Array (U.S.), Green Bank Telescope (U.S.), Haystack Radio Telescope (U.S.), Australia Telescope Compact Array (Australia), Mopra Radio Telescope (Australia), Parkes Radio Telescope (Australia), Korean VLBI Network (South Korea), The VLBI Exploration of Radio Astrometry Telescope (Japan), and Radio Telescope Effelsberg (Germany). Administrations are urged to take all practicable steps to protect the radio astronomy band at 42.5- 43.5 GHz from harmful interference (RR 5.149), and further regulations regarding acceptable power levels are mandated by RR 5.551I and RR 5.551H. This band is used for observations of silicon monoxide (SiO) masers that have rest-frame emission lines at 42.519, 42.821, 43.122, and 43.424 GHz. Measurement of SiO masers from stars and star-forming regions in our Milky Way galaxy yield important information on stellar temperature, density, wind velocities, precise astrometric positions and other parameters. Polarization observations are also used to trace the magnetic field distribution around the stars. Radiocommunication Conference 2019. Washington, DC: The National Academies Press. https://doi.org/10.17226/24899. p. 39. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 61

The 42.5-43.5 GHz band is also one of the preferred RAS bands for continuum observations (Recommendation ITU-R RA.314-10). Its location in the spectrum at approximately twice the frequency of the 23.6-24 GHz continuum band, and its 1 GHz bandwidth, makes it an effective point for sampling the continuum emission at octave or better frequency intervals. Because the sensitivity of continuum observations increases with the bandwidth of the observation, and because this band is the only RAS band below 75 GHz that is a full gigahertz wide, the band is extremely valuable scientifically. Continuum observations in this band provide critical information on the physical state of the interstellar medium associated with star-forming regions, and observations at this frequency have been used to measure the cosmic microwave background emission that reveals details of the early universe. The narrow RAS frequency allocation at 48.94-49.04 GHz is used to observe carbon monosulfide (CS) in the Milky Way galaxy. CS observations probe the dense interstellar medium that is the site of star-forming regions, including the formation of solar systems like our own. In addition, based on the observed isotope ratios of C32S, C33S, and C34S, radio astronomers are investigating theories of nucleosynthesis and the star-formation history of the Milky Way galaxy. In this band, Administrations are urged to take all practicable steps to protect the RAS from harmful interference (RR 5.149), and all airborne emissions are prohibited (RR 5.340). Furthermore, additional protections are stated in RR 5.555B, as follows: “the power flux density in the band 48.94-49.04 GHz produced by any geostationary space station in the FSS (space-to-Earth) operating in the bands 48.2-48.54 GHz and 49.44-50.2 GHz shall not exceed −151.8 dB (W/m2) in any 500 kHz band at the site of any radio astronomy station.” Also of concern, as noted in Resolution 159 (WRC-15), is the frequency range 51.4-54.25 GHz, which is used by RAS in some nations (RR 5.556). Recommendation: The committee recommends extensive study of the potential for interference into RAS and EESS (passive) sensors at these frequency bands. The introduction of aeronautical and maritime Earth stations in motion (ESIMs) operating in fixed-satellite service (FSS) bands adjacent to critical EESS and RAS primary bands poses a significant threat to these services and their ability to fulfill their vital missions in public safety and scientific research. The possibility that large numbers of mobile transmitters might simultaneously be in view of a protected EESS sensor or RAS observatory further enhances the threat of harmful interference. Guard bands protecting adjacent EESS and RAS protected spectrum, with out-of-band emission mask levels accounting for multiple simultaneously visible ESIM transmitters at maximum deployment levels, are the most robust means of protection. More complex dynamic frequency allocation schemes that rely on mobile stations to be aware of EESS satellite ephemerides and geofencing boundaries around RAS observatories are possible, but such schemes must be supported by regulatory and licensing measures that ensure that ESIM deployments do not grow over time into an uncontrolled and irreversible interference problem. Similarly, compatibility studies for additional allocations to the FSS must take into account the vulnerability of the radio astronomy service to spaceborne and airborne transmissions. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 62

WRC-27 AGENDA ITEMS 2.4, 2.5, and 2.7: 71–76 GHz AND 81–86 GHz Proposed WRC-27 Agenda Items 2.4, 2.5, and 2.7 include the following: • The introduction of power flux-density (pfd) and equivalent isotropically radiated power (e.i.r.p.) limits in Article 21 for the frequency bands 71-76 GHz and 81-86 GHz in accordance with Resolution 775 (WRC-19); • The conditions for the use of the frequency bands 71-76 GHz and 81-86 GHz by stations in the satellite services to ensure compatibility with passive services in accordance with Resolution 776 (WRC-19); • To consider the development of regulatory provisions for non-geostationary fixed-satellite system feeder links in the frequency bands 71-76 GHz (space-to-Earth and proposed new Earth-to-space) and 81-86 GHz (Earth-to-space), in accordance with Resolution 178 (WRC-19). As all of these agenda items involve the same 71-76 and 81-86 GHz frequency regions, they are considered jointly herein. Within these ranges, 74-76 GHz has a secondary allocation to SRS, involving space-to-Earth transmissions while RAS is co-primary with other services in 81-86 GHz. Additionally, just outside these ranges, RAS has a co-primary allocation with radiolocation at 76-77.5 GHz, and the 86- 92 GHz region is co-primary between EESS, RAS, and SRS (passive) with RR 5.340 all emissions prohibited protection. RAS observatories are to be protected from harmful interference in the frequency range 76-86 GHz (RR 5.149), and all emissions are prohibited from 86-92 GHz (RR 5.340). For the latter, the detrimental levels for continuum and spectral line radio astronomy observations are −228 dBW/(m2 Hz) and −208 dBW/(m2 Hz), for the average across the full 6 GHz band and the peak level in any single 1 MHz channel (Recommendation ITU-R RA.769, Tables 1 and 2, respectively). For EESS (passive), the Recommendation ITU-R RS.2017 interference limit in this band is −169 dBW in 100 MHz. Earth Exploration-Satellite Service The 81-86 GHz region lies directly adjacent to the 86-92 GHz region heavily used by LEO satellites measuring vertical profiles of atmospheric temperature and humidity. This region represents a local minimum in atmospheric opacity, a “window channel,” providing a baseline for contrasting with measurements in other spectral regions containing emissions from oxygen (for measuring atmospheric temperature) and water vapor (for measuring humidity). Without such baseline information, the relative contribution to signals in other spectral regions from water vapor, oxygen, from surface emissions and from cloud and precipitation emissions and scattering cannot be disentangled, particularly the contributions from the lowermost regions of the atmosphere. Furthermore, the ability to view down to Earth’s surface in this band makes it ideal for measuring low-altitude precipitation and cloud structure, making this band a unique resource for studies of extreme weather phenomena. Table 2.13 lists examples of current and planned EESS (passive) sensors observing in this band. In considering adjacent allocations to other services, the “all emissions prohibited” nature of the 86-92 GHz region must be borne in mind, potentially necessitating the introduction of guard bands and/or beam-steering and nulling approaches. Although Earth-to-space transmissions are naturally of the greatest concern, reflections from space-to- Earth transmissions have been observed at other frequencies by Earth-orbiting satellites, and sidelobe emissions and reflected/scattered primary beams from ground-to-ground transmissions are also a concern, particularly in aggregate. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 63

TABLE 2.13 EESS (Passive) Satellite Missions Relevant to WRC-27 Agenda Items 2.4, 2.5, and 2.7 Sensor Satellite Center Frequency (GHz) Bandwidth (MHz) AMSR2 JAXA GCOM-W1 23.8, 36.5, 89 400, 1000, 3000 AMSU-A, NOAA-15, NOAA-18, 23.8, 31.4, 50.3, 51.76, 270, 180, 180, 400, ATMS NOAA-19, NOAA-20, 52.8, 89.5 400, 5000 JPSS-2, JPSS-3; EUMETSAT MetOp-A, MetOp-B, MetOp-C; NOAA Suomi NPP GMI NASA GPM 23.8, 36.5, 89 400, 1000, 6000 MWI EUMETSAT MetOp-SG 23.8, 31.4, 50.3, 52.61, 400, 200, 400, 400, 89 4000 MWRI CMA FY-3C, FY-3D, FY- 23.8, 36.5, 89 400, 1000, 6000 3E, FY-3F, FY-3G; NSOAS HY-2A HY-2B SSM/I, SSMIS DoD DMSP F-15, 16, 17, 22.2, 37,a 50.3,b 52,b 85.5 401, 1600, 380, 389, 18 1500 MWI DoD WSF-M 23.8, 35.5-36.75, 37.0- 400, 500, 2500, 6000 37.75, 89.0 AMSR3 JAXA GOSAT-GW 23.8, 36.5, 89 400, 1000, 3000 MicroMAS-2 NASA TROPICS 90.255, 93.055 1000, 1000 NOTE: Italics denote missions in development. Acronyms are defined in Appendix B. a Department of Defense satellites operate outside the passive protected band and into a shared government use band. b Not every instrument in the list has every channel. SSM/IS has the full channel suite. Radio Astronomy Service The 71-76 GHz and 81-86 GHz spectral regions lie in an atmospheric transmission window between the nearly opaque spectral regions associated with the band of oxygen lines near 60 GHz and the isolated oxygen line at 118.75 GHz. This window is exploited by a number of radio observatories worldwide. At these frequencies, in the relatively dry conditions in which these observatories operate, water vapor and dry air absorption are low, so protection of these observatories from interference relies on terrain shielding and the inverse square law. Thus, consideration of RFI to the RAS must include analysis appropriate to the geographic location of the observatory. In the United States, these observatories include the Haystack Observatory (Massachusetts), 8 of the 10 sites of the Very Long Baseline Array (VLBA), the Green Bank Observatory in West Virginia, the Arizona Radio Observatory (ARO) 12 m located at Kitt Peak (Arizona), and the Yuan-Tseh Lee Array for Microwave Background Anisotropy (Hawaii). Internationally, they include the Large Millimeter Telescope (LMT, Mexico); Mopra and the Australia Telescope Compact Array (ATCA) in Australia; the Nobeyama 45 m Telescope in Japan; the Effelsberg 100 m Radio Telescope in Germany; the IRAM 30 m in Spain; the 12 m Greenland telescope currently sited at Thule; the Atacama Large Millimeter Array (ALMA) in Chile; the NOEMA interferometer on Plateau de Bure in France; the Onsala 20 m telescope in Sweden; the 32 m Noto Radio Observatory in Italy; Metsähovi Radio Observatory in Finland; Yebes Observatory in Spain; three telescopes of the Korean VLBI Network (KVN) and the Taeduk Radio Astronomy Observatory (TRAO) in Korea; the Delingha Observation Station and the planned Qitai Radio Telescope (QTT) in China; the Galenki RT-70 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 64

and Suffa RT-70 radio telescopes in Russia; and the Yevpatoria RT-70 radio telescope in Crimea. Specialized observatories dedicated to mapping the cosmic microwave background (CMB) emission exploit this window. These include the South Pole Telescope (SPT) and BICEP-Keck Array observatories at the South Pole; and the Atacama Cosmology Telescope (ACT), Cosmology Large Angular Scale Surveyor (CLASS), and POLARBEAR in northern Chile. As noted in Recommendation ITU-R RA.314-10, 76-77.5 GHz, 81-86 GHz, and 86-92 GHz constitute some of the most important high-frequency ranges for both continuum and line observations of celestial objects. Our growing understanding of star formation and stellar evolution is critically dependent on millimeter-wave observations. For example, looking back in cosmic time, highly red-shifted emission from strong spectral lines at higher rest frequencies in distant galaxies can be detected over the full range of the RAS allocations. Looking farther back still, to the very origins of the observable universe, the CMB telescopes exploit this spectral window to make broadband observations that advance our understanding of big bang cosmology and high-energy physics. Finally, a new scientific field, astrochemistry, has arisen from the discovery of a very wide range of complex molecules in space. Radio astronomy observatories are particularly vulnerable to out-of-band emissions, including the harmonics of mobile devices. Full consideration of the impact of new allocations must include the sum of aggregate interference from multiple devices, including in-band, out-of-band, and spurious emissions. Recommendation: The committee urges that a comprehensive study of in-band, out-of-band, and spurious emissions be an integral part of work on these future agenda items. The committee notes that radio astronomy observatories that operate at these high frequencies are usually located at high, dry sites so that little, if any, terrain shielding is in effect and there is little protection from atmospheric attenuation. For EESS (passive), the impact of any out-of-band emissions and spurious emissions into the adjacent 86-92 GHz bands are of prime concern. Thus, masking and/or beam-steering/nulling requirements will be required in order to protect the science services from spurious emissions into the passive bands. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 65

WRC-27 AGENDA ITEM 2.6: Space Weather Proposed WRC-27 Agenda Item 2.6 is “to consider regulatory provisions for appropriate recognition of space weather sensors and their protection in the Radio Regulations, taking into account the results of ITU Radiocommunication Sector studies reported to WRC-23 under Agenda Item 9.1 and its corresponding Resolution 657 (Rev.WRC-19).” The applicable topic from Agenda Item 9.1 is discussed above. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 66

WRC-27 AGENDA ITEMS 2.8 and 2.9: L-BAND and S-BAND Two of the proposed WRC-27 agenda items address frequency allocations within L band (1-2 GHz) and S band (2-4 GHz). Agenda Item 2.8 aims “to study the technical and operational matters, and regulatory provisions, for space-to-space links in the frequency bands [1 525-1 544 MHz], [1 545-1 559 MHz], [1 610-1 645.5 MHz], [1 646.5-1 660.5 MHz] and [2 483.5-2 500 MHz] among non-geostationary and geostationary satellites operating in the mobile-satellite service, in accordance with Resolution 249 (WRC-19) 7;” while Agenda Item 2.9 “consider[s] possible additional spectrum allocations to the mobile service in the frequency band 1 300-1 350 MHz to facilitate the future development of mobile-service applications, in accordance with Resolution 250 (WRC-19).” Resolution 249 (WRC-19) considers “that the definition of mobile-satellite service (MSS) in No. 1.25 includes communication between space stations; … that it is technically feasible for a lower orbital altitude non-GSO space station to transmit data to and receive data from a higher orbital altitude non- GSO or GSO space station when passing within the satellite antenna coverage beam that is directed towards the Earth; … [and] that there is a growing interest in utilizing space-to-space satellite links for a variety of applications.” Resolution 249 (WRC-19) also considers “that using the frequency bands 1 610- 1 645.5 MHz and 1 646.5- 1 660.5 MHz allocated to the MSS (Earth-to-space) for transmissions in the Earth-to-space direction from non-GSO MSS space stations towards MSS space stations operating in higher orbital altitudes, including GSO, may increase spectral efficiency in these frequency bands;” and “that using the frequency bands 1 525-1 544 MHz, 1 545-1 559 MHz, 1 613.8-1 626.5 MHz, and 2 483.5 -2 500 MHz allocated to the MSS (space-to-Earth) for transmissions in the space-to-Earth direction from MSS space stations operating at higher orbital altitudes, including GSO, towards non-GSO MSS satellites, may increase spectral efficiency in these frequency bands.” Resolution 249 (WRC-19) also recognizes “that it is necessary to study the impact on other services … taking into account applicable footnotes to the Table of Frequency Allocations, to ensure compatibility with all primary allocated services in these frequency bands and the adjacent frequency bands and avoid harmful interference; … that there should be no additional regulatory or technical constraints imposed on primary services to which the frequency band and adjacent frequency bands are currently allocated; … [and] that the sharing scenarios may vary widely because of the wide variety of orbital characteristics of the non-GSO MSS space stations.” In addition, Resolution 249 (WRC-19) recognizes “that out-of-band emissions, signals due to antenna pattern sidelobes, reflections from receiving space stations and in-band unintentional radiation due to Doppler shifts may impact services operating in the same and adjacent or nearby frequency bands.” In this context, it is important to note that RAS has co-primary allocations at 1610.6-1613.8 MHz and 1660-1670 MHz and that RR 5.402 notes that “the use of the band 2483.5-2500 MHz by the mobile-satellite and the radiodetermination-satellite services is subject to coordination under No 9.11A. Administrations are urged to take all practicable steps to prevent harmful interference to the radio astronomy service from emissions in the 2483.5-2500 MHz band, especially those caused by second-harmonic radiation that would fall into the 4990-5000 MHz band allocated to the radio astronomy service worldwide.” Resolution 250 (WRC-19) considers “that some administrations are considering the feasibility of spectrum refarming/relocating some services operations in portions of the frequency band 1 300-1 350 MHz for the land mobile service (LMS), which requires a significant investment; … that advanced spectrum sharing techniques are under development that could facilitate additional utilization of spectrum by a number of different services in operation; … [and] the need to protect existing services when considering frequency bands for possible additional allocations to any service.” Resolution 250 (WRC- 19) also recognizes “that No. 5.149 calls for administrations to take all practicable steps to protect the 7 As noted in Resolution 249 (WRC-19): “The appearance of square brackets around certain frequency bands in this Resolution is understood to mean that WRC-23 will consider and review the inclusion of these frequency bands with square brackets and decide, as appropriate.” PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 67

radio astronomy service from harmful interference in the frequency band 1 330-1 400 MHz, which includes spectral lines of importance for current astronomical investigations.” Allocations to the science services within L band and S band are used widely for both Earth remote sensing and radio astronomy. In particular, the high atmospheric transparency makes this frequency range ideal both for studies of the universe from the ground and for measurement of Earth’s surface properties from space. For example, within L band, the 1400-1427 MHz passive band, shared by RAS, EESS, and SRS, is foundational to many studies of faint naturally occurring radio emissions—from studies of Earth’s sea-surface salinity and soil moisture to studies of neutral hydrogen in the Milky Way and other galaxies. In the context of these two WRC-27 agenda items, several of the frequency bands under consideration are the same or adjacent to primary allocations to the science services. As listed in Recommendation ITU-R RA.769, the spectral power flux density considered harmful to radio continuum observations at 1665 MHz is −251 dBW/(m2 Hz). As listed in Recommendation ITU-R RS.2017, the maximum interference level into an EESS receiver is −174 dBW in a 27 MHz bandwidth at 1370-1427 MHz. The potential impact on EESS and RAS must be taken into consideration for these future WRC agenda items. Radio Astronomy Service The concern for radio astronomy regarding WRC-27 Agenda Item 2.8 is primarily a consideration of both direct illumination by space-to-Earth transmissions and reflections from Earth-to-space transmissions into radio astronomy receivers. The direction of transmission is critically important for consideration of compatibility with radio astronomy. In general, Earth-to-space transmissions can be coordinated geographically to protect radio astronomy facilities whereas space-to-Earth transmissions run the risk of including a radio astronomy facility within the beam of transmission. However, the proposed space-to-space transmissions introduce additional concerns. For example, depending on the incidence angle, space-based Earth-to-space transmissions may include radio astronomy facilities within their beam and may also result in high intensity reflections from satellites in the beam, resulting in scattered radiance into radio astronomy receivers. Thus, the compatibility between MSS Earth-to-space transmissions and RAS cannot be assumed a priori in the proposed application of space-to-space transmissions in the Earth- to-space direction. Further, while the consideration of space-to-space transmissions in the space-to-Earth direction will require the same type of compatibility studies as space-to-Earth transmissions, such studies must include the recognition that the geographic region illuminated by the satellite beam must be considered in addition to the location of the receiving satellite. In particular, the proposed space-to-space transmissions in the space-to-Earth direction will illuminate locations on Earth that are not targeted specifically and thus run the risk of direct illumination of radio astronomy receivers unless the geographic region illuminated is also considered. Of the frequency bands under consideration currently for WRC-27 Agenda Item 2.8, RAS is co- primary at 1610.6-1613.8 MHz and 1660-1670 MHz, both of which are also frequency bands listed in RR 5.149, where administrations are urged to take all practicable steps to protect radio astronomy. In addition, as noted in Resolution 249 (WRC-19), coordination with RAS is required for transmission at 2483.5-2500 MHz (RR 5.402), since the harmonics fall within the international secondary allocation of 4800-4990 MHz and the RAS co-primary allocation of 4990-5000 MHz. Note also that RAS has a co- primary allocation for 4950-4990 MHz in Argentina, Australia, and Canada (RR 5.443). In addition, the harmonics of 1630-1633.5 MHz correspond to the 3260-3267 MHz frequency band listed in RR 5.149, where administrations are urged to take all practicable steps. Further, as noted in RR 5.208B, Resolution 739 (Rev. WRC-15) applies to the bands 1525-1610 MHz and 1613.8-1626.5 MHz, with a maximum power flux density (pfd) of −194 dB(W/m2) in a 20 kHz bandwidth for unwanted emissions from a GSO station and a maximum equivalent power flux density (epfd) of −258 dB(W/m2) in a 20 kHz bandwidth for unwanted emissions from a non-GSO system. RR 5.372, 5.376A, 5.379A, and 5.379C have additional notations to protect the RAS in the 1610.6-1613.8 MHz and 1660-1670 MHz bands. Thus, the proposed transmissions from lower to higher orbit (i.e., in the Earth-to-space direction) for space-to-space links PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 68

between non-GSO and GSO MSS networks at [1610-1645.5 and 1646.5-1660.5 MHz] are potentially problematic for radio astronomy, while transmissions in the space-to-Earth direction for space-to-space links at [1613.8-1626.5 MHz] and [2 483.5-2 500 MHz] pose significant concerns regarding out-of-band emissions and spurious and unwanted emissions into RAS bands. L band and S band are workhorse frequency ranges for radio astronomy observations of faint cosmic sources. Within these frequency bands are significant spectral lines, including the spin-flip of neutral hydrogen with a rest frequency of 1420.4058 MHz and several different rotational transitions associated with the hydroxyl radical (OH) with rest frequencies of 1612.231, 1665.402, 1667.359, and 1720.530 MHz. The foundational science enabled by observations of the four L band transitions of the OH molecule includes study of the formation of proto-stars and the evolution of stars. These four transitions of OH are listed in Table 1of Recommendation ITU-R RA.314-10 as several of the radio-frequency lines of the greatest importance to radio astronomy. Measurement of the relative strength of several of these lines is necessary to interpret most observations made of the OH molecule. Thus, the loss of the ability to observe any one of these lines will hinder the ability to study these types of physical phenomena. In addition, the harmonics of transmissions at 1630-1633.5 MHz include the 3260-3267 MHz frequency band listed in RR 5.149, which is protected to enable observations of the 3263.794 MHz transition of methlyadyne (CH), which is also listed in Recommendation ITU-R RA.314 as a line of greatest importance to radio astronomy. Radio continuum observations at L band and S band include studies of pulsars, fast radio bursts, and synchrotron emission tracing relativistic plasma jets ejected from active galactic nuclei. In addition, as noted by RR 5.341, “in the bands 1400-1727 MHz [and others] passive research is being conducted by some countries in a programme for the search for intentional emissions of extraterrestrial origin.” One challenge for coordinated spectral sharing of these frequency bands is that observations in the L band and S band are sometimes conducted on targets of opportunity that are recently discovered (such as radio bursts or supernovae), transient in brightness or detectability (such as flares, active galaxies, or novae), and/or spatially transient due to the motion of the astronomical body (such as a comet). WRC-27 Agenda Item 2.9 considers new allocations to land mobile in 1300-1350 MHz, which overlaps the 1330-1400 MHz band protected by RR 5.149, where administrations are urged to take all practicable steps to protect radio astronomy. This frequency band is used primarily for observation of the redshifted 1420.4058 MHz neutral hydrogen line, shifted to lower frequencies in a manner similar to the Doppler effect, and for radio continuum observations of faint cosmic sources. As the most abundant element in the universe, observations of the neutral hydrogen line provide a unique trace of the gas content and kinematics of galaxies. However, due to the expansion of the universe, spectral lines for more distant objects are redshifted relative to their rest-frame transition frequencies and thus require access to lower frequency bands to detect these spectral lines in sources outside of the Milky Way galaxy. The large frequency band identified for redshifted neutral hydrogen observations enable measurement of the gas content of galaxies within a volume with a radius of approximately 1 billion light years. Prior protection of radio astronomy facilities from human-made emissions at these frequency bands was in part due to utilization of geographic shielding from fixed transmitters, which may not be possible if new applications are considered for mobile services. Careful consideration of the impact on radio astronomy facilities is required before new mobile allocations are made in this frequency band. Observations in the L band and S band are carried out at a number of radio astronomy sites in numerous countries, worldwide. In the United States, these include the VLA, the GBT, the Arecibo Observatory, 8 the Allen Telescope Array, and the 10 stations of the Very Long Baseline Array. Internationally, current facilities include the Nançay Radio Telescope (France), Jodrell Bank (United Kingdom), MERLIN (United Kingdom), the 100m Radio Telescope Effelsberg (Germany), the Westerbork Synthesis Radio Telescope (Netherlands), the stations of the European VLBI Network, Medicina Radio Observatory (Italy), the 64m Parkes Observatory (Australia), Australia Telescope 8 While the former 305-m telescope at Arecibo Observatory is no longer functional, a 12-m radio telescope is operational at the site and the observatory remains open. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 69

Compact Array (Australia), Australian Square Kilometre Array Pathfinder (Australia), stations of the Australian Long Baseline Array (Australia), MeerKAT (South Africa), FAST (China), the Russian VLBI network (Russia), the RATAN-600 (Russia), ROT-54/2.6 (Armenia), and the Brazilian Decimetric Array (Brazil). Earth Exploration-Satellite Service L band and S band are used in EESS passive remote sensing for monitoring soil moisture, sea surface salinity and sea ice. Although the majority of the frequency bands considered for WRC-27 Agenda Item 2.8 do not overlap with EESS (passive) allocations, WRC-27 Agenda Item 2.9 considers a frequency band that is adjacent to EESS (active) at 1215-1300 MHz. As discussed above in regards to WRC-23 Agenda Item 9.1b, the 1215-1300 MHz band is used to study Earth’s deformation due to earthquakes and tectonics as well as groundwater pumping. Current satellite missions include JAXA’s PALSAR, Argentina’s SAOCOM-1B, and the forthcoming NASA-ISRO NISAR. The data products from these missions are used for land classification, land-use change detection, surface soil moisture retrieval, and monitoring of crops and vegetation. In addition, reflected transmissions from radionavigation systems are received by Earth-orbiting sensors in a bistatic radar formation. These data are used in applications such as ocean wind-speed monitoring, used to track tropical storms, as well as monitoring soil moisture, vegetation, and crops. Also of note within the L band frequency range is the 1400-1427 MHz passive band allocated to EESS (passive), RAS, and SRS, where “all emissions are prohibited” (RR 5.340). Although none of the proposed frequency bands under consideration for WRC-27 Agenda Item 2.8 and Agenda Item 2.9 are adjacent to this passive band, it is important to note that contamination in these channels has been detected from out-of-band transmissions that have tapered (not sharp) spectra of emissions. RFI contamination of the SMAP and SMOS sensors, for example, has resulted in reduced quality and capability to monitor the variables that are used in weather and climate applications as well as natural hazards monitoring. The data stream from these satellites are the most reliable current source of surface soil moisture information that is used in Earth system science as well as impactful drought monitoring and flood forecasting natural hazards mitigation and must be protected from out-of-band and spurious emissions. Recommendation: Careful study will be required to ensure that there is no radio frequency interference introduced into RAS and EESS bands, particularly those adjacent to, or harmonics of, the proposed new allocations, as L band and S band are workhorse frequencies for both RAS and EESS. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 70

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Views of the U.S. National Academies of Sciences, Engineering, and Medicine on Agenda Items at Issue at the World Radiocommunication Conference 2023 Get This Book
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The radio frequency spectrum is a limited resource for which there is an ever-increasing demand from an expansive range of applications - all the way from commercial, such as mobile phones, to scientific, such as hurricane monitoring from space. Since radio waves do not stop at national borders, international regulation is necessary to ensure effective use of the radio spectrum for all parties. Use of the radio spectrum is regulated internationally by the Radio Regulations (RR), an international treaty. The International Telecommunication Union (ITU) has as its mission the facilitation of the efficient and interference-free use of the radio spectrum. Every 2 to 5 years, the ITU convenes a World Radiocommunication Conference (WRC) to review and revise the international RR. Changes to the RR are formulated through proposals to the conference according to Agenda Items, which are agreed on at the previous WRC.

At the request of the National Science Foundation and the National Aeronautics and Space Administration, this report provides guidance to U.S. spectrum managers and policymakers as they prepare for the 2023 WRC to protect the scientific exploration of Earth and the universe using the radio spectrum. This report identifies the 2023 agenda items of relevance to U.S. radio astronomers and Earth remote sensing researchers, along with proposed agenda items for the 2027 WRC.

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