Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses Second Edition (2015) / Chapter Skim
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3 Scientific Background: Earth Exploration Satellite Service
3 Scientific Background: Earth Exploration Satellite Service
Pages 52-85
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From page 52... ...
These services use spaceborne active and/or passive microwave sensors to provide valuable measurements of atmosphere, land, and sea, for both research and operational purposes. Because all matter emits, absorbs, and scatters electromagnetic energy to varying degrees, these sensors detect variations in Earth's environment.
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From page 53... ...
, and NASA's Soil Moisture Active/Passive (SMAP) are providing information about water, rainfall, and ocean salinity on a global basis to improve measurements of atmospheric temperature, water vapor and precipitation, soil moisture, concentrations of ozone and other trace gases, and sea surface temperature and salinity.
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From page 54... ...
Oxygen lines around 55 GHz are used to obtain atmospheric temperature profiles, and water lines are used to obtain atmospheric humidity profiles. The frequency allocations needed for these measurements are rigidly determined by the location of the resonant frequency bands.
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From page 55... ...
Salinity 2-10 Wind speed Redrawn Liquid clouds + Water vapor Tb 0 Frequency (GHz) Pi 10 20 30 40 Sea-surface temperature – FIGURE 3.3 Relative sensitivity of brightness temperature to geophysical parameters over ocean as a function of frequency.
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From page 56... ...
The dielectric constant of water is a strong function of frequency, temperature, and the water's phase. Frequencies below approximately 2 GHz are the most sensitive to sea surface salinity, while the frequencies closer to 5-10 GHz are the most sensitive to sea surface temperature.
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From page 57... ...
Applications of active sensors include the measurement of soil moisture and roughness, snow, ice, rain, clouds, atmospheric pressure, and ocean wave parameters, and the mapping of geologic and geodetic features and vegetation. Similar to passive requirements, the active sensor frequency and bandwidth requirements have been studied extensively by scientists, the results from which have informed the regulations at the ITU-R.
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From page 58... ...
The Special Sensor Microwave Imager/Sounder (SSMIS) , launched in 2003 on a DMSP satellite, observed atmospheric temperature up into the mesosphere as well as surface phenomena such as near-surface wind speed and sea surface temperature.
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From page 59... ...
3.2.2 Water Vapor Profiling The hydrologic cycle is critical to the dynamical and thermodynamical functioning of the global climate system and to its impacts on human society. The distributions of water vapor, cloud liquid water, and cloud ice in the atmosphere and the evolution of these distributions with time determine to a great extent the radia tion characteristics of clouds, with consequent large impacts on the radiation balance of the atmosphere.
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From page 60... ...
Passive measurements near the strong 183.31 GHz water-vapor line, aided by measurements in the adjacent transmission window at the EESS-allocated bands of 150-151 GHz or 164-168 GHz, are critical for the global measurement of atmospheric water vapor profiles. Measurements from spaceborne sensors in LEO are carried out to obtain atmospheric water-vapor profiles from Earth's surface to 100 mb with a measurement uncertainty of approximately 20 to 35 mb.
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From page 61... ...
Satellite-based microwave remote sensing of precipitation can provide the best-available means of obtaining data detailing four-dimensional distribution of rainfall and latent heating on a global basis.2 Rainfall and snowfall rates and total amounts of 2 For background information regarding EESS for precipitation and clouds, see the following: G.L. Stephens and C.D.
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From page 62... ...
Passive microwave measurements near the 89 GHz atmospheric window play an important role in the retrieval of precipitation data, particularly over land. Owing to the combination of high emissivity, thickness, and temperature of clouds over land, signatures of convective precipitation cells are often strongest at 89 GHz.
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From page 63... ...
Passive microwave remote sensing from satellites and aircraft at frequencies above 90 GHz are used to estimate hydrometeor properties of cirrus clouds and the higher altitude convective and anvil clouds, which contain frozen particles. Specific frequencies currently used include 150 GHz, 166 GHz, 183.31 GHz, 220 GHz, 325 GHz, 340 GHz, 380 GHz, 424 GHz, ~500 GHz, and 640 GHz.
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From page 64... ...
The monitoring of water vapor and cloud water content and their effects on global radiation fluxes is thus critical to understanding the causes of climate change and predicting future climates. Currently, cloud coverage and type are the most significant sources of uncertainty in global climate modeling.
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From page 65... ...
Future global CIWP measurements from space, using passive microwave techniques at frequencies from 89 GHz up to approximately 1 THz (e.g., 150, 166, 183, ~220, and ~340 GHz) could characterize the coupling of the global hydrologic and energy cycles through upper tropospheric cloud processes.
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From page 66... ...
Measurements of cloud liquid water will be needed to diagnose and validate these cloud models, which in principle have the ability to greatly improve understanding of climate, rainfall variability, and the atmospheric radiation budget. The inclusion of cloud water into numerical weather-prediction models will also provide an important means of accurately FIGURE 3.9 Combined imagery from Cloudsat and Japanese Multifunctional Transport Satellite (MTSAT)
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From page 67... ...
In this section, we briefly survey ongoing work and point out the wide range of frequencies below 3 GHz that are used for ionospheric sensing. Passive microwave techniques involve monitoring of the radio spectrum, radio imaging and interferometry, precision measurement of radio noise, and passive use of transmitters of opportunity (natural or man made)
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From page 68... ...
Transmission at low power covering the entire frequency range can be very useful for high measurement speeds. Similar to ionosondes, they provide measurements of electron density and reflection height, wave measurements, meteor trails, and Doppler radar measurement of coherent scattering structures.
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From page 69... ...
3 Radiometry in the 1-2 GHz range is arguably the best means for measuring subsurface soil moisture on a national or global basis. A combination of active and/or passive microwave measurements can be used to remotely sense SM under moderately vegetated areas, with up to ~5 kg/m2 of vegetation water content.
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From page 70... ...
Spectral gradients between various frequency combinations at 6, 10, 18, 22, and 37 GHz have been used to obtain freeze-thaw. 3.3.3 Surface Water Fresh water is essential to all life forms.
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From page 71... ...
Sea ice, frozen sea-bed, and icebergs constitute the oceanic elements of the cryosphere. This definition of Earth's cryosphere implies that substantial portions of Earth's land and ocean surfaces are directly subject in some fashion to cryospheric processes.
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From page 72... ...
4 Table 3.1 provides current RF sensors supporting cryosphere research. 3.4.1 Glaciers and Ice Sheets Glaciers and ice sheets are reservoirs of fresh water with greater than 90 percent of Earth's fresh water bound in the Antarctic Ice Sheet.
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From page 73... ...
Comparisons between modeled and SMOS measured brightness temperatures at 1.4 GHz offer some support for the hypothesis. 3.4.2 Sea Ice and Icebergs Sea ice modulates polar climate by restricting the oceanic heat flow to the atmosphere and by reflecting incoming solar radiation back into the atmosphere.
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From page 74... ...
Cloud cover and the long polar night dictate the use of all-weather, day/night passive microwave radiometers for monitoring sea ice age, extent, and concentration. Older, multiyear sea ice is thicker and is structurally different from new sea ice.
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From page 75... ...
More rapid shrinkage of the ice cover began in about 2000, and that trend is continuing through the present. Conversely, Antarctic sea ice is slowly expanding over the Southern Ocean.
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From page 76... ...
The start of ice formation and the start of springtime ice breakup are proxy indicators for changes in local climate as well as impacts on the ability to navigate these waterways. On larger lakes, passive microwave adiometry r is effective for monitoring lake ice growth and decay in much the same way as the technique is applied to sea ice.
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From page 77... ...
Parameter 1.4 5.3 6.8 10.7 13.6 18.7 23.8 37.0 Passive Sea surface temperature ● ○ ○ ○ ○ Sea surface winds ○ ● ○ ○ Sea surface salinity ● Active Surface topography ○ ● ○ ○ ○
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From page 78... ...
Ocean circulation in turn is responsible for moving large amounts of heat around the globe with an impact on local weather and climate. Sea surface salinity is also important for understanding the global hydrologic cycle.
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From page 79... ...
FIGURE 3.15 Remote sensing of sea surface salinity is important to improve understanding of ocean circulation and the global water cycle, and their role in climate and climate change. This image is an example of data produced by Aquarius.
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From page 80... ...
The Aquarius scatterometer operated at 1.26 GHz in a shared band is an example of combined active/passive microwave remote sensing.6 Data from both sensors are needed for an accurate measurement. Measuring sea surface salinity also depends on ancillary information such as surface temperature, atmospheric attenuation, and knowledge of radiation from other sources (e.g., the Sun and galactic background)
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From page 81... ...
. The calculations are for a surface with sea surface salinity = 35 psu and sea surface temperature = 20°C.
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From page 82... ...
Observation systems themselves have also benefited from historical resources, TABLE 3.3 Frequencies Where Most of the Active Science-Application Systems Operate for Studying the Solid Earth and Biosphere Band Designation Passive Spectra Active Spectra Role P-band 432-438 MHz Biomass imaging, root zone soil moisture, below canopy surface topography L-band 1.42 GHz 1215-1300 MHz Biomass imaging, forest change detection, surface motion and subsidence S-band 3100-3300 MHz Agricultural monitoring C-band 5250-5570 MHz Agricultural monitoring, surface change detection X-band 8550-8650 MHz, Vegetation and elevation mapping 9300-9900 MHz Ka-band 35.5-36 GHz Surface water and elevation mapping
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From page 83... ...
Department of Agri 7 For background regarding EESS in understanding surface dynamics and deformation, see the following: D Massonnet and K.L.
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From page 84... ...
The ability to perform comprehensive inventories of biomass from space is recognized as a critical step toward modeling and understanding Earth's climate system. Passive microwave observations operating in all of the primary atmospheric window channels between 1.4 and 90 GHz are valuable for monitoring the full range of vegetation canopy water content found in nature and are complementary to optical and synthetic aperture radar techniques.
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From page 85... ...
The proportional reduction in daily GPP shows where environmental conditions are less than optimal for plant growth (including areas with frozen temperatures and low soil moisture levels determined from SMAP active and passive microwave remote sensing; observed GPP reduction map ranges from optimal (100%) to fully constrained (0%)
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