AGENDA ITEM 1.11: 23 GHZ SPACE RESEARCH SERVICE UPLINK

Agenda Item 1.11 seeks to consider a primary allocation to the space research service (Earth-to-space) within the band 22.55-23.15 GHz, taking into account the results of ITU R studies, in accordance with Resolution 753 (WRC 07).

The primary concern is the 22.21-22.5 GHz band, which has a co-primary allocation between the EESS and RAS passive services and the fixed and mobile services, except for aeronautical mobile services. To protect EESS satellite observations from interference, ITU-R RS.1029 recommends a maximum interference level in the 22.21-22.5 GHz band of -249 dBW/Hz, with this interference level not to be exceeded for more than 0.1 percent of the sensor viewing area or measurement time. In this band, ITU Radio Regulations Footnote 5.149 states that “administrations are urged to take all practicable steps to protect the radio astronomy service from harmful interference. Emissions from spaceborne or airborne stations can be particularly serious sources of interference to the radio astronomy service.” The proximity of the proposed communication uplink to the allocated 22.21-22.5 GHz band increases the risk that out-of-band emissions will interfere with EESS and RAS passive services. The chance of interference depends upon the density of the communication transmitters and their locations.

In this context, a recent paper submitted to US Working Party 7B (US WP7B/062, Update to WRC-12 Agenda Item 1.11 CPM Text) predicts, “The number of SRS earth stations transmitting in the 22.55-23.15 GHz band will be small. … The number of SRS earth station sites capable of supporting Lunar and/or L2 missions is not expected to exceed eight or nine on a global basis. A similar number of SRS earth stations may support low Earth orbiting (LEO) missions, also on a global basis. These earth stations are typically located in rural, isolated areas at mid latitudes.” However, EESS passive observations from satellites are made on a global basis and could experience interference from even one earth station, regardless of its geographic location. Microwave radiometers from the U.S. Air Force, Navy, DOD, NOAA, NASA and other federal agencies have been making space-borne observations near 22 GHz since the Nimbus E Microwave Spectrometer was launched in 1972. EESS satellite sensors shown in Table 2.6 are currently observing in the allocated 22.1-22.5 GHz band.

Passive microwave observations of water vapor are important in part because weather radars measure only the reflectivity of water/ice droplets in the atmosphere. Extraction of useful information from radar reflectivity measurements relies greatly on knowledge of the droplets’ size distribution, which requires complex and costly multiband radar measurements to directly measure. Passive microwave instruments, on the other hand, directly measure the total quantity of liquid water as well as water vapor and other variables. Such radiometers can herald impending weather events by measuring the presence of water vapor in advance of cloud formation, and then detect the formation of liquid water droplets well in advance of detection by rain radars. Moreover, when used in conjunction with weather radars, passive radiometers provide a high degree of precision in the measurement of the path- or area-averaged quantities being observed that serve to calibrate the radar’s signal. In this manner the radiometer is able to facilitate the radar’s capability to provide high resolution measurements.1

TABLE 2.6 EESS Passive Sensors Using the Spectrum between 22 and 24 GHz

Sensor Satellites (currently on orbit) Agencies Minimum Frequency (GHz) Maximum Frequency (GHz)
SSMIS DMSP F16 U. S. Air Force 22.04 22.44
SSM/I DMSP F13 and F15 U.S. Air Force 22.11 22.36

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1 National Research Council, Spectrum Management for Science in the 21st Century, The National Academies Press, Washington, D.C., 2010, p. 24-25.



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