Asymptotic approximations for wave scattering from rough surfaces: Range of valid application as determined by numerical electromagnetic techniques

Remote sensing of ocean surface winds and waves is based on knowledge of scattering from rough surfaces. Virtually all remote sensing applications make use of either the physical optics approximation (quasispecular scattering), the small perturbation approximation (Bragg scattering), or the two-scale approximation. Since the criteria for the validity of these approximations are not well understood, we investigate these approximations by numerical electromagnetic techniques. Using the method of moments with Monte Carlo techniques, we calculate the radar cross section for a one-dimensional random rough surface with a given power spectrum. This cross section is then compared with one-dimensional cross sections calculated by physical optics, small perturbation theory, and the two-scale approximation with the goal of finding limits of validity for these approximations.