A practical cross-section for scattering from rough surfaces at very low grazing angles in both the forward and backward directions

Abstract

In this paper we develop an extension of the small slope approximation (SSA) for scattering from randomly rough Dirichlet surfaces, which includes some multiple scattering. This extension is designated by SSA+. We focus on scattering at very low grazing angles where multiple scattering of both the incident and scattered fields is of importance. Numerical results for the SSA+ bistatic scattering cross-section for very low forward grazing angles are presented using the Gaussian roughness spectrum and for both very low forward and very low backward grazing angles using the Pierson–Moskowitz and modified power law spectra. The results are restricted to an angle of incidence of 80°. It is shown that when the lowest-order SSA gives reasonably accurate results, the SSA+ increases the accuracy up to at least the final 0.2° of grazing in the forward direction. In the backward direction, the SSA+ gives good results for the Pierson–Moskowitz spectrum, but the results are less dramatic.

Acknowledgments

This research was supported by the Office of Naval Research, Code 321OA. The authors would like to express their appreciation for significant contributions to this work by a number of people including Dr Eric I. Thorsos of the University of Washington Applied Physics Laboratory, Dr Alexander G. Voronovich of the National Oceanic and Atmospheric Administration, Prof. Joel Johnson of Ohio State University who generously shared Fortran code with us, and Ms M. Carolina Parada who is currently studying at Johns Hopkins University.