Theoretical study of the sensitivity of the microwave backscattering coefficient to the soil surface parameters

The microwave backscattered signal from soil is sensitive to surface parameters and especially to roughness and moisture. The object of this work is to evaluate the optimum operating configuration for a spacecraft radar which would allow the extraction of one of these parameters, minimizing the effect of the other. A theoretical study, using a simulation model based on the scalar approximation, has permitted the estimation of the backscattering coefficient's sensitivity to a relative variation in soil parameters in terms of radar characteristics. The results show that, if a very low incidence angle is not acceptable, the best configuration for a soil moisture measurement requires the simultaneous use of two polarizations (HH and VV) and a large look-angle (>35°). For a roughness measurement, the coupling of two incidence angles (20° and 40°), a low frequency (S or C-band) and the HH polarization seem to give satisfactory results.