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** PREPUBLICATION COPY – WORDING SUBJECT TO CHANGE ** Agenda Item 8.2: Next WRC Agenda Item “recommend[s] to the Council items for inclusion in the agenda for the next WRC, and to give its views on the preliminary agenda for the subsequent conference and on possible agenda items for future conferences, taking into account Resolution 806 (WRC 07).” Secondary allocation to EESS (passive) of a 200 MHz bandwidth located between 6.425 and 7.250 GHz Recommendation ITU‐R RS.1029 states that 200 MHz of bandwidth between 6.425 and 7.250 GHz is required for sea surface temperature and soil moisture remote sensing. Radio Regulations footnote 5.458 recognizes the current use of this frequency range for remote sensing of sea surface temperature and states, “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 6.425‐7.025 MHz and 7.075‐ 7.250 MHz.” Recommendation: AA secondary allocation for EESS (passive) between 6.425 and 7.250 GHz should be sought to normalize the radio regulations with the current and planned practical passive use of the spectrum for Earth observation. Following the launch of NASA’s EOS Aqua in 2002 and Navy’s WindSat in 2003, radiometers have been passively using the spectrum near 7 GHz to measure soil moisture and sea surface temperature on a global basis. Table 8.2‐1 below lists current and future U.S. EESS passive sensors using this band. The satellites mentioned in Table 8.2‐1 will have benefits that reach far beyond the countries that funded them. Soil moisture is a key factor in evaporation and transpiration at the land‐atmosphere boundary. Due to the large amount of energy required to vaporize water, soil moisture has a large influence on both surface energy and carbon fluxes at the Earth’s land surface. Sea surface temperature provides critical information on the ocean surface thermal state, which plays an important role in the transpiration of gases at the air‐sea boundary. Such air‐sea interactions are important in climate studies. Furthermore, since the density of water is determined by its temperature and salinity, sea surface temperature is a key determinant of waves and currents in response to external forces. Passive microwave measurements of sea surface temperature in the 7‐GHz band “see through” nearly all clouds and precipitation. Such all‐weather coverage permits measurement of the ocean surface during and after hurricanes and tropical cyclones, which often spawn cirrus clouds that block geostationary weather satellites from viewing the surface at visible and infrared wavelengths from one day to about a week. Table 8.2‐1: EESS Passive Sensors using the Spectrum between 6.425 and 7.250 GHz Sensor Satellites Minimum Maximum Frequency Frequency (GHz) (GHz) WindSat Coriolis 6.737 6.863 40
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** PREPUBLICATION COPY – WORDING SUBJECT TO CHANGE ** AMSR‐E42 EOS Aqua 6.750 7.100 Table 8.2‐2: EESS Passive Sensor under Development to Use the Spectrum between 6.425 and 7.250 GHz Sensor Satellites Minimum Maximum (under development) Frequency Frequency (GHz) (GHz) MIS JPSS 6.450 6.800 42 AMSR‐2 on GCOM‐W1, set for launch in early 2012, is a follow‐on to AMSR‐E and is planned to operate at two center frequencies of 6.925 and 7.3 GHz. SOURCE: http://sharaku.eorc.jaxa.jp/AMSR/AMSR2_RA/documents/GCOM_RA1_E.pdf; last accessed on June 18, 2010. 41
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** PREPUBLICATION COPY – WORDING SUBJECT TO CHANGE ** Overarching Issues The preceding sections have dealt with specific agenda items. In this section, we wish to provide some additional comments that are relevant to all agenda items. These comments are intended to provide a broader understanding of the issues unique to the Radio Astronomy Service (RAS) and the Earth Exploration‐Satellite Service (EESS). Radio frequency interference is a substantial concern to the passive scientific services, RAS and EESS. The 2010 U.S. National Research Council report, Spectrum Management for Science in the 21st Century,43 found that “[i]mportant scientific inquiry and applications enabled by the Earth Exploration‐ Satellite Service (EESS) and the Radio Astronomy Service (RAS) are significantly impeded or precluded by radio frequency interference (RFI). Such RFI has reduced the societal and scientific return of EESS and RAS observatories and necessitates costly interference mitigation, which is often insufficient to prevent RFI damage.” RAS Radio astronomy deals with exceedingly weak signals. These signals can be a million times smaller than the internal receiver noise, and their measurement, or even just their detection, can require bandwidths of many gigahertz, and integration times of a day or more. This requirement puts a premium on operating in a very low noise environment. It should be emphasized that serious interference can result from weak transmitters even when they are situated in the sidelobes of a radio astronomy antenna. This state of affairs has been recognized by the International Telecommunications Union (ITU) internationally and by the FCC in the United States, and various spectral bands have been allocated to the RAS for “exclusive” or “shared” use of these bands. However, “exclusive” does not mean that there is zero emission in the protected bands. It is a fundamental fact that any information‐carrying signal can contain out‐of‐band emission, which spreads across a wide radio spectrum. The regulation of this out‐ of‐band emission from a licensed transmitter involves controlling the intensity of the emission, and the FCC definition leads to an allowable level that, unfortunately, can cause serious interference with radio astronomy observations. It is likely that this situation will become worse in the future, as the RAS requirements become stricter with the study of weaker sources, and at the same time the active services are proliferating. Recommendation ITU‐R RA.769 discusses interference protection criteria for the Radio Astronomy Service and defines threshold levels of emissions that cause interference detrimental to radio astronomy. Our knowledge of the chemical makeup of the universe comes though measurements of narrow spectral lines arising from quantum mechanical transitions. Radio spectroscopic observations require measurements at frequencies determined by the physical and chemical properties of individual atoms and molecules, so it is important to protect the frequencies characteristic of most important atomic and molecular cosmic constituents. However, the necessary parameters are not known for all possible species of interest. 43 National Research Council, Spectrum Management for Science in the 21st Century, The National Academies Press, Washington, D.C., 2010. 42
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** PREPUBLICATION COPY – WORDING SUBJECT TO CHANGE ** The situation with continuum (broad band) observations of radio emission from cosmic thermal and nonthermal sources, however, is different from that for spectral lines. There are no preferred frequencies, but observations at multiple strategically‐spread frequencies are required to define the properties of stars, galaxies, quasars, pulsars, and other cosmic radio sources. Moreover, due to the expansion of the universe, even the spectroscopic lines may be Doppler shifted as much as a factor of five or more, and broad bandwidths are also employed to simultaneously study many spectral lines. Historically narrow bands spaced throughout the spectrum have been given various levels of protection to enable these important studies. However, improvements in antenna and receiver design now permit instantaneous bandwidths up to about 30 percent to be used in the new generation of radio telescopes. This results in up to an order of magnitude improvement in sensitivity over earlier narrow band systems suggesting that a new paradigm for spectrum management will be needed to enable further advances in radio astronomy. Transmissions from satellites and aircraft for the purposes of communications and operations, and their dramatic growth in recent years, are prime concerns for RAS. For cost and technical reasons, these transmissions must be powerful enough to be usefully received by small omnidirectional antennas on Earth. Thus, high transmitter powers are necessary, but have the potential to create interference to RAS if unwanted emissions outside the necessary bandwidth are not sufficiently limited in the RAS observing bands. Because aircraft and satellites, in particular, know no geographical boundaries, the remote location of the telescope sites provides no protection from such sources when in direct line of sight above the horizon. Future progress in radio astronomy at these frequencies may largely depend on national and regional protection of large frequency bands in the vicinity of major radio telescopes along with global regulations of transmissions from satellites and aircraft. EESS Recommendation ITU‐R RS.1029 provides the protection criteria for the Earth Exploration Satellite Service. The high radiometric accuracy and sensitivity achieved by current EESS systems results in commensurately high sensitivity to RFI that can cause errors in the retrieved geophysical parameters. The ultimate impact of such emissions on a specific EESS geophysical measurement depends on the sensitivity of the geophysical parameter to changes in brightness temperature, as discussed in §2.2 of Spectrum Management for Science in the 21st Century. The maximum signal‐power contamination that can exist without impacting the information contained in the EESS measurement has been derived by EESS scientists for each of the EESS allocated bands and is documented in Recommendation RS.1029. Over the last decade the rate‐of‐occurrence of harmful interference in EESS allocations between 1.4 GHz and 18.7 GHz has increased. When compared with historical data, the level and rate of interference appears to be on the rise. Specifically, satellites observing within the allocations at 1400 MHz, 10.65 GHz, and 18.7 GHz receive harmful interference on daily to weekly basis. Thus, both interference from unwanted emissions and from transmissions in shared allocations by both ground and space‐based sources are of concern to the EESS. Spurious and Out of Band (OOB) transmitter emissions from commercial devices typically are neither precisely controlled during manufacture nor essential to the devices’ intended purposes. Even when 43
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** PREPUBLICATION COPY – WORDING SUBJECT TO CHANGE ** false measurements due to RFI are detected and eliminated, measurements and their use are degraded by the loss of data. 44