Passive microwave emission from smooth bare soils: developing a simple model to predict near surface water content
MICRO-SWEAT is a coupled microwave emission and soilvegetation-atmosphere transfer scheme. It can predict, among other things, the L band (21 cm wavelength) microwave brightness temperature (TB) for a smooth bare soil from knowledge of the soil hydraulic properties and local meteorological data. TB is the product of the apparent emissivity (eapp) and the effective physical temperature of the soil profile (Teff). The modelled relationship between e app and average 0-2 cm soil water content was used to develop a simple semi-empirical model, which predicts the near surface water content from knowledge of the particle size distribution and eapp. Teff was found to be comparable to the soil temperature at 11 cm depth, and was estimated using a simple sinusoidal function based on thermal diffusivity to extrapolate the temperature at 11 cm depth from knowledge of the diurnal variation in air temperature. The dependence of TB on incidence angle was predicted by MICRO-SWEAT and also incorporated. This simple model was then successfully used to predict the 0-2 cm water content from knowledge of TB, the air temperature regime and the particle size distribution, for data collected at various look angles over three different soils using a truck-based radiometer.
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Document Type: Research Article
Publication date: 2001-12-15