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2 The Earth Exploration-Satellite Service
Pages 18-87

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From page 18...
... . Modern observation systems offer economically and societally important forecasts extending farther into the future than ever before, but these advances depend on protected radio frequency allocations.
From page 19...
... Scientists can thus extract information from the radio spectrum on environmental properties as varied as atmospheric temperature and humidity, precipitation rate, soil moisture, ocean salinity, and ocean waves (and therefore surface winds and
From page 20...
... • 1940-1945: Wartime studies of centimeter- and millimeter-wave atmospheric absorp tion spectra and passive radiation; the development of sensitive radiometry. • 1968: Launch of the first passive microwave radiometer on the Soviet Cosmos-243 satellite -- it observed sea surface temperature, land temperature, snow/ice cover, water vapor, and liquid water using four unscanned window channels at 3.5-37 GHz (unfor tunately short-lived, operating only for weeks)
From page 21...
... Land is denoted by shades of gray, its shade depending on the elevation; sea ice is denoted by white. AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs Figure 2-2 DISCOVER Project and the AMSR-E Science Team.
From page 22...
... Consistent with this assessment of the importance of climate to humanity are estimates that the potential consequences of global change in its various manifestations (sea ice loss, global warming and drought, coral bleach ing, tropical ecosystem collapse, and other interrelated environmental problems) would be associated with unprecedented societal costs to the United States and the world.3 These staggering costs demand that the most precise information on global environmental processes be made available to decision makers grappling with questions of environmental policy.
From page 23...
... 2.1 SPECIFIC APPLICATION AREAS OF PASSIVE MICROWAVE REMOTE SENSING Earth remote sensing is critically important to the United States and to the advancement of human scientific knowledge about Earth and the environmental processes that support life and commerce. Microwave remote sensing, or the Earth Exploration-Satellite Service (EESS)
From page 24...
... Passive microwave sensors are particularly critical for measur ing temperature, humidity, and precipitation profiles in the cloud-affected tropo sphere below approximately 10 km, where most economically important weather occurs, and in measuring sea surface winds and temperatures and soil moisture. Part of the reason for this importance is that weather radars measure only the reflectivity of water and ice droplets in the atmosphere but are insensitive to these other parameters.
From page 25...
... and the CloudSat and future Aquarius and Soil Moisture Active Passive (SMAP) missions.
From page 26...
... Current atmospheric models tend to use sea surface temperatures (SSTs) as their primary boundary condition because so much of Earth's surface is
From page 27...
... Figure 2-4 A B C R01628 editable vector type overlies bitmapped images FIGURE 2.5 The value of soil moisture data to climate forecasts. Predictability of seasonal climate is dependent on boundary conditions such as sea surface temperatures (SST)
From page 28...
... Passive microwave radiometers operating at frequencies of 10 GHz and lower are sensitive to variations in soil density, type, and moisture content and are needed for SM measurements. Radiometry in the 1-2 GHz range is arguably the best means for measuring subsurface soil moisture on a national or global basis.
From page 29...
... As in the case of temperature profile measurements, combined microwave and infrared spectral data can yield what is nearly all-weather global performance, even in most cloudy conditions. Two different types of microwave observations are used: those in transparent bands within which the water vapor absorption stands out (1)
From page 30...
... . Instruments retrieving water vapor profiles are generally used to retrieve other parameters simultaneously, such as cloud water content, precipitation rate, and ice and snow cover information.
From page 31...
... Figure 2-7 R01628 of today's 4-day forecasts is about the same as the 2-day forecasts of 20 years ago.7 EESS measurements have played a le vector image editab major role in improving these forecasts. The insurance industry is also increasingly interested in using passive microwave data to arbitrate claims involving hurricane-related flooding or winds that can often only be distinguished by passive microwave observations.
From page 32...
... The cold wake was invisible to AVHRR because of persistent clouds and rain. A retrospective analysis showed that the magnitude of the cold wake left by Hurricane Bonnie was critical to being able to predict the weakening of the second hurricane, Danielle, a few days later and could not have been done without the microwave measurements of sea surface temperature by TMI.8 The strong dependence of hur ricane growth on local sea surface temperatures makes such measurements through hurricane cloud shields important, particularly since the overturning of the water by the hurricane itself can alter those temperatures rapidly.
From page 33...
... , observed by passive microwave radiometers on2-9a (left) a Naval Research Laboratory satellite, as Katrina makes landfall Figure WindSat, Figure 2-9b (right)
From page 34...
... Radar observations are strongly dependent on unknown drop size distributions, and optical sensors do not penetrate clouds well; thus microwave radiometers on all types of platforms (satellite, aircraft, ships, and ground sites) are essential to making water vapor measurements and thus to the science of climate change.
From page 35...
... As ice clouds can reflect a significant amount of sunlight, their impact on global radiative energy fluxes and hence climate change is consider able. Future global IWP measurements from space using passive microwave tech niques at frequencies from 89 GHz up to approximately 1 THz could characterize the coupling of the global hydrologic and energy cycles through upper tropospheric cloud processes.11 Such measurements would enable the development and testing of new self-consistent parameterizations of ice cloud processes and cloud systems, which could in turn guide improvements in ice cloud representation in global Earth system models.
From page 36...
... -- has been able to monitor the rise in global sea level, thus providing an important means of verifying the expansion of the oceans in response to climate change. These missions have also contributed significantly to the ability to forecast the occurrence of El Niño events as much as 1 year in advance.16 For each radar observation, coincident passive microwave radiometer measurements are needed in order to correct the radar altimeters' determination of sea level for the variations in integrated atmospheric refractivity due to tropospheric water vapor.17 These refractivity radiometers operate near 19, 23 and 34 GHz and require measurements of brightness temperature that are free of radio frequency interference (RFI)
From page 37...
... data are derived using microwave imagery that is sensitive to emission from different snow depths and structure, in combination with visible imagery. In 2004, a global monthly SWE climatology data set that blended Scanning Multi Channel Microwave Radiometer (SMMR)
From page 38...
... Pro Figure 2-10 vided by the National Snow and Ice Data Center. R01628 uneditable bitmapped images Glaciers Passive microwave sensors can perform spatial mapping of the amount of snow overburden and the melt state of large ice sheets such as those over Green land and Antarctica.
From page 39...
... The combination of global sea surface salinity and sea surface temperature measurements can be used to determine seawater density, which regulates ocean circulation and the formation of water masses. Sea Ice One of the first applications of space-based passive microwave imagery was that of monitoring the location, extent, and thickness of sea ice.
From page 40...
... Passive microwave observations from space -- augmented by radar -- are the primary means for observing the freeze-thaw transi tion on a global scale.24 Determining the freeze-thaw transition requires the use of all of the primary atmospheric window channels between 1.4 and 90 GHz, up to and exceeding the EESS allocated bandwidth on primary or secondary basis.25 Biomass Earth's vegetation canopy, or biomass, is a significant component of the global carbon inventory. It is also a major contributor to the net long-wave/short-wave albedo of the planet and hence to Earth's energy balance and temperature.
From page 41...
... Other passive microwave products can be used to monitor the size, nutrient status, and other health mea sures of forests, crops, and vegetation; changes in vegetation type, deforestation, and other land cover; and geographic characterization of the "footprints" of urban areas. Urban and suburban areas play an often-overlooked but important role in Earth's physical and ecological systems, adding to the understanding of mesoscale climatic, hydrologic, and ecologic processes.28 Box 2.2 summarizes typical uses of EESS data in reservoir management, the deployment of renewable energy systems, and agricultural forecasting, as reported in a recent evaluation of uses of Earth observations by the U.S.
From page 42...
... Inputs to RiverWare include microwave data from the Advanced Microwave Scanning Radiometer-Earth (AMSR-E) and data from other sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS)
From page 43...
... Surface-based, upward-looking microwave radiometers have the unique ability to remotely detect supercooled liquid water that adheres to aircraft flight surfaces and helicopter rotors, and which has been responsible for numerous losses of aircraft and lives. These same radiometers also improve the skills of the forecasters of short-term local aviation weather.
From page 44...
... In another episode, on March 4, 2003, light, freezing drizzle was foreseen, detected, and tracked by a research microwave radiometer monitoring surface based temperature, water vapor, and cloud liquid water. This condition caused the failure of six jet engines owing to the ingestion of ice on United Airlines (UAL)
From page 45...
... . For example, the Special Sensor Microwave/Imager Sounder radiometer, which is aboard a DSMP satellite, measures atmospheric temperature and moisture profiles, sea surface winds, cloud liquid con tent, and land surface parameters on a continuous basis from low Earth orbit.
From page 46...
... . 36 Group on Earth Observations, "Declaration of the Earth Observation Summit," Washington, D.C., July 31, 2003, available at http://earthobservations.org/docs/Declaration-final%207-31-03.pdf; accessed December 30, 2009.
From page 47...
... global competitiveness and defense. In addition to radio science education, the application of passive microwave radiometry to environmental monitoring provides a key means of training Earth scientists.
From page 48...
... 2.2 BRIGHTNESS TEMPERATURES, GEOPHYSICAL MEASUREMENTS, AND MISSIONS Section 2.1 established the range of applications and the importance of passive microwave radiometry. This section describes the processes by which these sensors operate, providing detailed information on the specific geophysical measurements that result.
From page 49...
... Although multiple geophysical parameters may affect the brightness tempera ture -- for example, the temperature and moisture level of Earth's surface and the temperature, humidity, and cloud properties of the atmosphere -- these parameters can be distinguished when they have distinctive frequency and/or polarimetric signatures, so that simultaneous observations of the brightness temperature at multiple frequencies and polarizations enable simultaneous solutions for the geophysical properties of interest. There exists a long history of innovation in pas sive microwave EESS observations for solving this multiple-parameter estimation problem.
From page 50...
... It is possible to estimate these two unknown abundances because the lower frequency is near the 22.235 GHz water vapor resonance, whereas at 37 GHz cloud absorption is relatively stronger. Observations at the two bands yield two relations that can be inverted to find the two unknowns, that is, the amounts of water vapor and liquid water.
From page 51...
... Because all window channels exhibit some atmospheric absorption and emission, and even atmospheric resonant fre Salinity Wind speed Liquid clouds + Water vapor Tb Frequency (GHz) 0 Pi 10 20 30 40 Sea-surface temperature – FIGURE 2.11 Ocean scene: relative sensitivity of sea surface salinity, sea surface temperature, cloud liquid water, and integrated water vapor as a function of frequency for space-based measurements.
From page 52...
... Because the estimates of the geophysical parameters, also called Environmental Data Records (EDRs) , are computed as a function of observed brightness temperatures, it is possible to find the average ratio of a change in a spe cific EDR to the corresponding change in a particular brightness temperature.
From page 53...
... . Since current scientific requirements for climate studies include retrievals of SST accurate to within 0.5 K or better, radio frequency interference that causes a 0.25 K change in 5 GHz brightness temperatures would pose a major problem for the retrieval of accurate sea surface temperatures.
From page 54...
... , allocation heat exchange, storm tracking and forecasting, climate operations Sea surface NWP, storm tracking, 10.7 18.7 23.8 37 Moderate-low: over ocean, some winds operations sea (sea) potential for RFI at 10.7 GHz Sea ice Climate, operations 18.7 37 Low: higher frequencies and remote concentration locations Sea ice age Climate, operations 18.7 37 Low: higher frequencies and remote locations
From page 55...
... In the columns "Earth ExplorationSatellite Service Passive Microwave Frequencies" and "Summary of RFI Potential," red indicates high RFI potential, yellow indicates moderate RFI potential, and green indicates low RFI potential. The colors in between (red-yellow and yellow-green)
From page 56...
... 50-60 Minimum observed Atmospheric temperature profile SSM/I (3 current, 4 past) 19.35, 22.2, 37, 85.5 23 GHz RFI possible from Ocean wind speed, integrated water vapor, cloud vehicle anticollision radar liquid water, precipitation SSM/T (3 current, 5 past)
From page 57...
... 19.35, 22.2, 37, 50-60, 91.6, 23 GHz RFI possible from Ocean wind speed, atmospheric temperature and 150, 183.31 vehicle anticollision radar moisture profile, integrated water vapor, cloud liquid water, precipitation MHS (2 current) 89, 150, 183.31 Minimum Atmospheric moisture profile MLS (1 current)
From page 58...
... Microwave array spectrometer Minimum High-frequency, all-weather temperature and humidity sounds for weather forecasting and sea surface temperature SCLP (1) Ku- and X-band radars; K- Possible RFI experience Snow accumulation for freshwater availability and Ka-band radiometer similar to that of WindSat NOTE: SST (*
From page 59...
... Since then, EESS has continued to fly passive microwave radiometers with ever-increasing capability and covering an expanding range of frequencies. Of note is the current interest in measurements of 1.4 GHz and 6.8 GHz brightness temperature to sup port sea surface salinity and soil moisture measurements, critical to the continued improvement of weather and climate measurements as described in §2.1, with additional background supplied in Appendix E
From page 60...
... program, which employs ground-based up-looking passive microwave sensors to characterize the global radiation budget and clouds. These unattended systems continuously measure water vapor profiles and cloud liquid water accurately and inexpensively, relative to radiosondes.
From page 61...
... It presents both specific examples of RFI impacts on Earth observations and justified concerns about future sources of interference. Introduction to the Problem of Radio Frequency Interference: Immediate Impacts on EESS EESS radiometers measure the naturally generated background brightness temperature (noise power)
From page 62...
... Phalippou, "Variational Retrieval of Humidity Profile, Wind Speed, and Cloud Liquid-Water Path with the SSM/I: Potential for Numerical Weather Prediction," Quarterly Journal of the Royal Meteorological Society, 122: 327-355 (1996)
From page 63...
... Observations at 1.4 GHz over land by ground-based and airborne systems in support of remote soil moisture and sea surface salinity estimation are often com promised by what can be identified as OOB emissions from active systems. Total in-band emissions must remain below approximately –140 dBm from 1400-1427 MHz to ensure that anthropogenic (i.e., human-made)
From page 64...
... D.M. Levine, "Aquarius: An Instrument to Monitor Sea Surface Salinity from Space," IEEE Transactions on Geoscience and Remote Sensing, 45(7)
From page 65...
... showing the effects of radio frequency interference (RFI) at 1413 MHz in the vicinity of Richmond, Virginia.
From page 66...
... . The vertical lines west of Oklahoma City are distortions due to radio frequency interference (RFI)
From page 67...
... X-Band (0.-0. GHz) Passive microwave observations at X-band are critical for measurements of sea surface winds (useful for weather prediction and storm tracking)
From page 68...
... , from Figure 1.) AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team.
From page 69...
... AMSR-E data are pro duced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team. Data are available at www.remss.com.
From page 70...
... Data are available at www.remss.com. the western Atlantic off the coast of Brazil being unavailable for sea surface wind, temperature, and heavy rain measurements, as shown in Figure 2.18.46 Southerly views of upwelling microwave brightness temperatures are typically measured by polar-orbiting EESS satellites in the descending phases of their orbits, so such RFI is typically observed in half of all such data over the Mediterranean Sea.
From page 71...
... This level 0.2 K, the minimum level of perturbation that degrades environmental models that use sea surface R01628 temperature data derived from AMSR-E. AMSR-E data are produced by Remote Sensing Systems and uneditable bitmapped image sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team.
From page 72...
... K-Band (.-. GHz) The 18.6-18.8 GHz band is a critical resource for EESS that supports many operational environmental products, such as snow cover, sea surface wind speed, and soil moisture measurements.
From page 73...
... Naval Research Laboratory. Figure 2-20c&d R01628 uneditable bitmapped image
From page 74...
... water vapor/cloud liquid measurements within the midlatitude coastal environment is about 0.6 K on humid days. Higher RFI levels of up to 1 K can be tolerated for observations of integrated liquid water in clouds and rain where the atmospheric signals are higher.
From page 75...
... C-band measure ments from AMSR-E and WindSat currently provide critical SST products over ocean sufficiently far from the coasts. Ongoing improvements in maritime prod uct accuracies, particularly in near-shore sea surface temperature measurements improved to 0.1-0.2 K accuracy, may thus become limited in the near future by RFI, even far out at sea.
From page 76...
... AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team. Data are available at www.remss.com.
From page 77...
... 1979 and (B) 1987, showing no noticeable brightness temperature from radio frequency interference (RFI)
From page 78...
... Currently, no federal agency or other organiza tion systematically measures temporal spectrum use.50 Finding: Better utilization of the spectrum and reduced radio frequency inter ference for scientific as well as commercial applications are possible with better knowledge of actual spectrum usage. Progress toward the goal of improved spectrum usage could be made by gather ing more information through improved and continuous spectral monitoring.
From page 79...
... Finding: There is currently inadequate protected spectrum in C-band and X-band for operational passive microwave observations of sea surface temperature, soil moisture, and ocean surface wind speed and direction. Finding: While unilateral radio frequency interference mitigation techniques are a potentially valuable means of facilitating spectrum sharing, they are not a substitute for primary allocated passive spectrum and the enforcement of regulations.
From page 80...
... Automotive collision-avoidance radars that employ the entire 22-27 GHz range have recently been included on new vehicles and are becoming widespread. In particular, the FCC's 2002 approval of the use of UWB devices in the 3-10.6 GHz band and of anticollision radar operation as Part 15 devices near 24 GHz has alarmed the EESS community.52,53 These sources produce broadband signals that resemble thermal noise, making them difficult to distinguish from natural emissions.
From page 81...
... In addition, there is great concern for the future of EESS measurements of opportunity at C-band. This band covers much of the spectral region commonly used by EESS for measurements of sea surface temperature and soil moisture on an as-available basis.
From page 82...
... in the future and that the nominal tolerable RFI level for these systems will be 0.02 K For a typical five-channel 22 GHz to 30 GHz upward-looking water vapor profiling radiometer, 1 K of RFI in a channel near the center of the 22.235 GHz water vapor line can induce a 10 percent error in retrieved water vapor abundance in the lower and mid-level troposphere.
From page 83...
... Other Concerns SST Measurements at C-Band and X-Band (-0 GHz) Of particular future concern is RFI affecting continuous all-weather microwave sea surface temperature measurements in littoral regions that are critical for severe storm forecasting and weather and climate studies (see Figure 2.8)
From page 84...
... Members of the EESS passive community raised this issue in comments filed in response to the FCC's NPRM, and the FCC's decision is still forthcoming as of the time of this writing.57 The community is also interacting with IEEE standards organizations to determine the possible impact of such wire less systems on future EESS observations.58 It is clear that RFI degradation of EESS measurements and weather forecasting services appears to be likely if widespread unlicensed transmissions in these bands begin. Consideration should be given to limiting the strength and density of trans mitters in this band (see Appendix C)
From page 85...
... The frequency requirements of those measurements are dictated by molecular quantum transitions of the gases under consideration. Trace gases of particular interest include ozone, chlorine, hydrogen, bromine, and water vapor.
From page 86...
... TABLE 2.4 Submillimeter Infrared Radiometer Ice Cloud Experiment (SIRICE) Instrument Spectral Coverage and Sensitivity Requirements for Measurement of Ice Water Path NE∆T (K)
From page 87...
... Successes • European and Japanese transition to 77 GHz band for automobile radar, avoiding 23-24 GHz. • The development of airborne sub-band-based radio frequency interference (RFI)


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