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This is the first in a series of two papers on the use of active microwave remote sensing for measuring the moisture content of bare (Part I) and vegetation-covered (Part II) soil. An experimental program was conducted to evaluate the response of the backscattering coefficient to soil moisture content as a means to specify radar system parameters for future airborne and/or spaceborne soil moisture mappers. Particular attention was paid to the effects of surface roughness, and a preliminary examination of the role of soil texture was performed. The results of this investigation confirm the findings of a previous experiment 1 which concluded that the effects of surface roughness can be minimized by operating at a frequency in the neighborhood of 5 GHz over the 7-17° angle of incidence range. The precision with which soil moisture in the surface soil layer can be estimated is comparable to the precision of the ground-truthed estimate. Because the moisture in the surface layer is highly correlated to the subsurface moisture, it was not possible to determine experimentally the effective depth of the layer responsible for the observed radar backscatter.
Ulaby et al. (Sun,) studied this question.