Application of beam simulation to scattering at low grazing angles: 2. Oceanlike surfaces

Abstract

The beam simulation method developed by Maystre and Saillard is applied to one‐dimensional power law surfaces with the same dielectric properties and average spatial wave number content as wind‐driven ocean waves. In the beam simulation method the scattering from overlapping surface subsegments is first computed and then coherently combined to obtain the scattered field. The beam simulation method is generally more efficient than the method of moments, but it is not an exact numerical method. Thus we have developed a measure of the minimum subbeam size that can be used for improved efficiency. This measure can be interpreted as the maximum distance on the surface over which local structures interact. We find that the maximum interaction distance at 80° incidence can be as large as 200λ, and it increases with increasing incidence angle. As large‐scale surface waves begin to dominate the surface structure, significant departures from the behavior predicted by first‐order perturbation theory are observed within the accurate computation range of low grazing angle backscatter. The results are discussed in light of ocean scattering data that evidently cannot be explained by existing theories.