APPLICATION OF BEAM SIMULATION TO SCATTERING AT LOW GRAZING ANGLES .2. OCEANLIKE SURFACES

The beam simulation method developed by Maystre and Saillard is applie d to one-dimensional power law surfaces with the same dielectric prope rties and average spatial wave number content as wind-driven ocean wav es. In the beam simulation method the scattering from overlapping surf ace subsegments is first computed and then coherently combined to obta in the scattered field. The beam simulation method is generally more e fficient than the method of moments, but it is not an exact numerical method. Thus we have developed a measure of the minimum subbeam size t hat can be used for improved efficiency. This measure can be interpret ed as the maximum distance on the surface over which local structures interact. We find that the maximum interaction distance at 80 degrees incidence can be as large as 200 lambda, and it increases with increas ing incidence angle. As large-scale surface waves begin to dominate th e surface structure, significant departures from the behavior predicte d by first-order perturbation theory are observed within the accurate computation range of low grazing angle backscatter. The results are di scussed in light of ocean scattering data that evidently cannot be exp lained by existing theories.