Backscatter measurements of soil surfaces at millimeter wave frequencies

The measured backscattering coefficients of three sandy soil surfaces are presented. The measurements were conducted using 35 and 94 GHz polarimetric scatterometers. The measured backscattering coefficients are compared to those predicted by the classical surface scattering models (physical optics and geometric optics). Furthermore, the results are compared to a recently developed empirical model based on observations made at microwave frequencies. Preliminary analysis shows that none of the above models is capable of predicting the measured backscattering coefficients accurately and that volume scattering from the voids inside the soil layer, computed via the radiative transfer theory, must be considered. It is shown that a combination of surface and volume scattering terms will adequately characterize the backscattering from soil surface at millimeter wave frequencies.<>