Issues in the Integration of Research and Operational Satellite Systems for Climate Research Part I. Science and Design (2000) / Chapter Skim
Currently Skimming:
Soil Moisture
Soil Moisture
Pages 68-81
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 68... ...
Though of relatively small total quantity, water in the terrestrial regime plays an active role in the global hydrologic cycle and is estimated to contribute 21 percent of global precipitation and 14 percent of global evapotranspiration. The horizontal and vertical distributions of soil moisture exert control over the partitioning of incoming radiant energy into latent and sensible heat fluxes via evaporation and transpiration by plants.
|
From page 69... ...
Most of these fit under the following four science issues: · Understanding the role of surface soil in the partitioning of incoming radiant energy into latent and sensible heat fluxes at a variety of scales, from the mesoscale to general circulation model (GCM) scale; · Understanding the relationship between the moisture in the top 5 cm of soil that is observable by microwave techniques and the total profile (1 m or more)
|
From page 70... ...
, which may allow the mapping of soil moisture for bare soil surfaces and for surfaces with short vegetation cover. To map soil moisture under a wide range of vegetation-cover conditions (but still limited to grasses and cultural vegetation)
|
From page 71... ...
microwave radiometeris particularly suited for mapping sparsely vegetated terrain at resolution scales in the range of 10 to 20 km. The next three subsections discuss passive microwave remote sensing as a potential technique for mapping the distribution of soil moisture, active microwave remote sensing, and the complementarily of the two techniques.
|
From page 72... ...
that it is possible to use an L-band radiometer for mapping soil moisture "over a range of cover conditions and within reasonable error bounds" (Jackson and LeVine, 1996~. The first objective led to the development of an aircraft-mounted system called the Electronically Scanned Thinned Array Radiometer, or ESTAR.
|
From page 73... ...
SOIL MOISTURE FIGURE 6.1 Surface soil moisture images for Washita '92 (Jackson and LeVine, 1996~.
|
From page 74... ...
- , Ho . FIGURE 6.2 Ground verification of soil moisture estimation algorithm (Jackson and Le Vine Active Microwave Sensing Bare-Soil Surfaces The backscattering coefficient c,° measured by a radar system whose antenna beam is pointed at a bare-soil surface is governed by two physical parameters: the volumetric moisture content mv and the rms surface roughness s, and to a much lesser extent by soil type.
|
From page 75... ...
The synthetic aperture radar (SAR) observations were extracted from several AirSAR campaigns and from Shuttle Imaging Radar-C overpasses in April 1994 (Ulaby et al., 1996~.
|
From page 76... ...
Complementarily of Active and Passive Microwave Observations Table 6.1 summarizes the sensor configurations appropriate for passive and active microwave techniques for mapping the distribution of soil moisture. To produce soil moisture maps with 10-km pixels from a satellite altitude of 600 km, a passive microwave radiometer would need an antenna 15 to 20 m in diameter or a rectangular aperture of comparable dimensions.
|
From page 77... ...
SOIL MOISTURE FIGURE 6.5 Measured versus predicted vegetation water mass (mw) and soil moisture (my)
|
From page 78... ...
OBSERVING STRATEGY OF CURRENT AND FUTURE SATELLITE SENSORS Sensors Currently in Use Of the passive microwave sensors currently flying aboard orbiting satellites, none operates at the L-band (1 = 21 cm) and none is suitable for soil-moisture mapping.
|
From page 79... ...
in the high-resolution mode and electronically scanned thinned array radiometer (ESTAR)
|
From page 80... ...
Experimental work conducted at Texas A&M and the University of Kansas in the 1970s using truck-mounted radiometer and scatterometer observations of agriculture crops showed similar reductions in sensitivity to soil moisture for both the active and passive microwave techniques. Recent theoretical treatment of the issue also confirms that the masking effects of vegetation are similar for radiometers and radar in most instances (Du et al., 2000~.
|
From page 81... ...
1993. Measuring surface soil moisture using passive microwave remote sensing.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.