Comparison of unified full-wave solutions for normal incidence microwave backscatter from sea with physical optics and hybrid solutions

The unified full-wave solution for electromagnetic wave scatter from a rough surface is expressed as an integral similar in form to physical optics solutions. However it correctly predicts return for small and intermediate roughness scales where the physical optics approach fails. This full-wave solution is used here to evaluate microwave sea surface backscatter at normal incidence for both the like-and cross-polarized linear components. Surface heights and slopes are assumed to be Gaussian, the sea is characterized by its surface height spectral density function and both perfectly and finitely conducting surfaces are considered. Results from this complete full-wave evaluation are compared with approximations, involving single-scale (specular point) and two-scale models. For both of these models, however, it is necessary to assume a spectral wavenumber, νd, where spectral splitting between the large and the small scales of the rough surface occurs. The full-wave solution is used as a guide in the selection of νd and to study the accuracy and sensitivity of the different approximations to νd. It is also shown that results for cross-polarized backscatter based on the physical optics or two-scale models are totally inadequate.