Numerical simulation of scattering from simple and composite random surfaces

Numerical simulation studies of backscattering from one-dimensional, statistically known, perfectly conducting random surfaces are carried out to examine (1) the scattering characteristics in the intermediate-frequency region, where neither the low- nor the high-frequency approximation is applicable, (2) the validity of the two-scale concept in rough-surface scattering, and (3) applicability of the wavelength filtering concept to simple and composite surfaces. It is found that in the intermediate-frequency region the angular scattering curves for both the horizontal and vertical polarizations decrease at a slower rate than that predicted by a first-order small perturbation solution and that the Kirchhoff solution always lies between the two polarizations. In addition, the level difference between the horizontal and vertical polarization scattering coefficients is smaller than that of the perturbation solution. The two-scale concept has no general applicability. Its application is restricted to two-scale surfaces where one scale satisfies the Kirchhoff approximation and the other the small perturbation assumptions such that the two scales dominate scattering in different angular regions. The concept of wavelength filtering is applicable to simple surfaces or to each component of a composite surface in the low-frequency region where scattering is dominated by a narrow band of surface frequency components but loses its validity gradually as we approach the high-frequency limit where scattering is determined by the surface slope distribution. It is not the explanation of why the surface components of a composite surface may dominate scattering over different angular regions.