A comparison of models for predicting near-specular bistatic scattering from rough surfaces

This paper provides a comparison of scattering models for near-specular bistatic scattering from rough surfaces. While the Geometrical Optics (GO) approximation is widely accepted for surfaces having large roughness compared to the electromagnetic wavelength, small differences in the literature exist between GO formulations. The Physical Optics (PO) and Small Slope Approximation (SSA) methods are also available and may provide differing predictions for moderately non-specular geometries. Comparisons of these models are reported in this paper, with a particular emphasis on analysis of near-specular surface scattering returns obtained from the GNSS-R mode of the radar receiver in NASA's Soil Moisture Active/Passive (SMAP) mission.