Views of the U.S. NAS and NAE on Agenda Items at the World Radiocommunication Conference 2015 (2013)

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Introduction

The World Radiocommunication Conference (WRC), a gathering of official delegations from over 140 nations, is organized by the International Telecommunication Union (ITU). These delegates come together every few years to negotiate proposals to change international radio spectrum regulations, which, if approved, would then be in force internationally through the auspices of the ITU. These proposals, called agenda items, are not brought to the WRC spontaneously; they must have been agreed on at a previous WRC in order to be considered at the subsequent WRC. In the interim between the two conferences, national governments work internally and with their regional counterparts to develop a consensus position on each proposal to the extent possible given varying national priorities and interests. The national delegates then bring their positions to the WRC and negotiate with other delegations before a final vote on each proposal in carried out.

Agenda items are typically very specific in nature and propose narrow but potentially substantial changes to the use of the spectrum that can have a significant impact on users. Since the vast majority of spectrum allocations are for the active use of the spectrum, it is

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NOTE: Portions of this text are taken from National Research Council, Views of the NAS and NAE on Agenda Items at Issue at the World Radiocommunication Conference 2012, The National Academies Press, 2013.

critical for vulnerable passive (or, receive-only) services to voice their concerns about potentially adverse effects on their operations.¹

The passive Radio Astronomy Service (RAS) and the Earth Exploration-Satellite Service (EESS) provide scientific observations of the universe and Earth through the use of advanced receiver technology with extreme sensitivity and complex noise reduction algorithms. Even with such technology, RAS and EESS are seriously adversely affected by what most active services would consider extremely low noise levels.²

EARTH EXPLORATION-SATELLITE SERVICE

Satellite remote sensing is a uniquely valuable resource for monitoring the global atmosphere, land, and oceans. Passive instruments are particularly vulnerable to man-made emissions within the EESS bands because they rely on very small signals emitted naturally from Earth’s surface and its atmosphere and because they look everywhere (i.e., they monitor globally). Passive remote sensing from satellites provides information that is critical to human welfare and security. This includes information to predict weather and climate and to understand climate change. Examples are parameters such as ocean temperature, salinity, and surface wind speed, needed to understand ocean circulation and the associated global distribution of heat. Passive remote sensing is also important for monitoring soil moisture, a parameter needed for monitoring and predicting agricultural productivity for food security; for land use; for the assessment, adaptation, and risk management of hydrological extremes such as drought and floods; for weather prediction (heat exchange with the atmosphere); and even for defense (planning military deployment). Passive sensors also provide temperature and humidity profiles of the atmosphere, used for weather forecasting, and gather information to monitor changes in the polar

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¹ In the United States, the Radio Astronomy Service (RAS) and the Earth Exploration-Satellite Service (EESS) are allocated 2.07 percent of the spectrum on a primary basis and 4.08 percent of the spectrum below 3 GHz on a secondary basis. Allocations for RAS and EESS are comparable in the ITU’s international allocation tables. From National Research Council, Spectrum Management for Science in the 21st Century, Washington, D.C.: The National Academies Press 2010, pp. 137 and 138.

² Spectrum management in the context of the scientific services is discussed in National Research Council, Spectrum Management for Science in the 21st Century, Washington, D.C.: The National Academies Press, 2010; National Research Council, Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses, Washington, D.C.: The National Academies Press, 2007; and “Radio Frequencies: Policy and Management” (2013), to appear in IEEE Transactions in Geoscience and Remote Sensing (TGARS).

ice cover and information needed in assessing hazards such as hurricanes, wildfires, and drought.

For many applications, satellite-based microwave remote sensing represents the only practical method of obtaining atmospheric and surface data for the entire planet. Major U.S. governmental users of EESS data include the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), the Department of Defense (especially the U.S. Navy), the Department of Agriculture, the U.S. Geological Survey, the Agency for International Development, the Federal Emergency Management Agency (FEMA), and the U.S. Forest Service. Much of this data is available free to anyone anywhere in the world.

It is evident that some of these valuable measurements are being corrupted by radiofrequency interference (RFI). For instance, the Soil Moisture and Ocean Salinity (SMOS) mission and the Aquarius mission, operating at 1.413 GHz in a band protected for passive use only, and the Advanced Microwave Scanning Radiometer (AMSRE), operating at 10.7 GHz, cannot retrieve soil moisture in some areas of the globe because of RFI. Figure 1.1 shows the impact of RFI as observed by the Aquarius satellite. In addition to the RFI effects on passive instruments, recent measurements from active remote sensing instruments³ have also been found to be affected by RFI.

RADIO ASTRONOMY SERVICE

Radio astronomy is a vital tool used by scientists to study our universe. For example, it is the most promising way of mapping out the Epoch of Reionization (EoR), which refers to the period in the history of the universe shortly after the big bang when the first luminous sources emerged. Radio astronomy also provides valuable data for the benefit of society, such as the monitoring of solar flares and sunspots. Such monitoring allows for 1-4 day forecasts of geomagnetic disturbances that can affect the operation of satellite communications, Global Positioning System (GPS) navigation systems, and terrestrial power grids, as well as the safety of astronauts engaged in space walks. It was through the use of radio astronomy that scientists discovered the first planets outside the solar system, circling a distant pulsar. Subsequent observations of pulsars have revolutionized our understanding of the physics of neutron stars

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³ Active remote sensing involves sending a signal, receiving the reflected signals, and analyzing them. Radar is the prime example of active remote sensing.

FIGURE 1.1 Percentage of samples flagged as RFI. This is data from the Aquarius radiometer, which operates in the band at 1.413 GHz protected for passive use only (Le Vine et al., IEEE TGARS 45, 2007). The radiometer observes the Earth with a footprint diameter of about 100 km. Each observation is tested for RFI, and the map shows the percentage of samples identified as RFI and therefore removed from data processing. The map illustrates the magnitude of the problem even in a band protected for passive use. The map is similar to observations by the SMOS L-band radiometer (Oliva et al., IEEE TGARS 50, 2012). RFI is much more prevalent over the land than over the ocean, but it is also a problem over the ocean. For example, the figure shows RFI over the North Atlantic and along the coasts of Greenland and North America. SOURCE: David Le Vine, NASA Goddard Space Flight Center.

and have resulted in the only experimental evidence so far for gravitational radiation.

Radio astronomy has also enabled the discovery of organic matter and prebiotic molecules outside our solar system, leading to new insights into the potential existence of life elsewhere in our galaxy. Measurements of radio spectral line emission have identified and characterized the birth sites of stars in the galaxy, the processes by which stars slowly die, and the complex distribution and evolution of galaxies in the universe.

Radio astronomy measurements have discovered the cosmic microwave background (CMB), the radiation left over from the original big bang after it cooled to only 2.7 K. Later observations discov-

ered the weak fluctuations in the cosmic microwave background (CMB) of only one-thousandth of a percent, generated in the early universe. These later formed the stars and galaxies we know today. Radio observations uncovered the first evidence for the existence of a black hole in our galactic center, a phenomenon that may be crucial to the creation of galaxies. Observations of supernovas have allowed astronomers to witness the distribution of heavy elements essential to the formation of planets like Earth, and of life itself.

Spectrum Sharing and the Scientific Services

The critical science undertaken by Earth remote sensing scientists and radio astronomers cannot be performed without access to interference-free spectrum. Notably, the emissions that radio astronomers receive are extremely weak—a radio telescope receives less than one hundredth of a percent of one-billionth of one-billionth of a watt (10^–20 W) from a typical cosmic object. Because radio astronomy receivers are designed to pick up such remarkably weak signals, they are particularly vulnerable to interference from in-band emissions, spurious⁴ and out-of-band⁵ emissions from licensed and unlicensed users of neighboring bands and from emissions that produce harmonic signals in the RAS bands. Out-of-band emissions can exist anywhere in the spectrum. Even weak, distant, man-made signals can preclude scientific use of the spectrum. Similarly, since remote sensing scientists observe the noise floor generated by natural (thermal) radiation and the extremely weak variations therein, their observations are also very vulnerable to interference from man-made transmissions. ITU Recommendations RA.769, RS.1029 and RS.2017 provide technical recommendations on levels that allow reasonable shared use of the spectrum in the context of the passive scientific services.

Moving to other bands is not always a viable option. To fulfill

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⁴Out-of-band emission: emission on a frequency or frequencies immediately outside the necessary bandwidth which results from the modulation process, but excluding spurious emissions (definition taken from Rec. ITU-R SM.1541-4). Necessary bandwidth is defined in Rec. ITU-R SM.1541-4 as “the width of the frequency band which is just sufficient to ensure the transmission of information at the rate and with the quality required under specified conditions [for a given class of emission].”

⁵Spurious emission: emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products, and frequency conversion products but exclude out-of-band emissions (definition from Rec. ITU-R SM.1541-4).

their scientific missions, radio astronomers and remote-sensing scientists must often observe at the specific frequencies characteristic of elements, ions, or molecules, which are established by the laws of physics and chemistry.

To ensure their ability to use the radio spectrum for scientific purposes, scientists must participate in the discussion in the lead-up to the WRC-15, which will next be held in November 2015 in Geneva, Switzerland. At the request of NSF and NASA, the U.S. National Research Council (NRC) convened a committee to provide guidance to U.S. spectrum managers and policy makers as they prepare for the WRC-15 to protect the scientific exploration of the Earth and universe using the radio spectrum (see Appendix for the committee’s Statement of Task). While the resulting document (the present report) is targeted at U.S. agencies, representatives of foreign governments and foreign scientific users may find its contents useful as they plan their own WRC positions.

This report identifies the agenda items of relevance to and potentially impacting U.S. radio astronomy and Earth remote sensing observations. The sections are laid out serially in numerical order to facilitate locating a specific agenda item. The committee has determined that the agenda items given in Table 1.1 could, if agreed on as proposed, impact RAS and EESS operations. This report discusses only those agenda items that the committee believes most important and most deserving of comment at the current time. The committee does not comment on the communication of scientific data (i.e., space-to-Earth, Earth-to-space, and space-to-space), because this topic is not within its purview and as such the membership was not composed to address it. It is noted that impact is assessed on criteria related to in-band, out-of-band, and spurious emission as appropriate. For purposes of providing information, it is also noted where a proposed change would impact common practice.

The committee advocates for effective use of the electromagnetic spectrum across all services. This shared use of the spectrum is coupled with a shared responsibility to ensure continued availability of this critical resource for effective use by all.

TABLE 1.1 WRC-15 Agenda Items With Potential Impact on RAS and EESS