Numerical study of shadowing in electromagnetic scattering from rough dielectric surfaces

A numerical study has been performed to examine the effects of surface self-shadowing on the electromagnetic scatter from rough dielectric interfaces. A hybrid numerical technique combining the moment method and geometrical theory of diffraction was used in the numerical calculations. This technique was first extended to be applicable to general dielectric media as well as perfectly conducting and high loss, high permittivity surfaces. The numerical calculations show that weakly shadowed small-scale roughness can contribute significantly to the backscatter at extreme grazing angles. This effect is more pronounced at VV polarization than at HH polarization when the surface is perfectly conducting, but is approximately the same at both polarizations when a finite-conductivity interface is considered. Scattering models that depend on a shadowing function based on geometrical optics are likely to fail at extreme grazing angles for lossy dielectric as well perfectly conducting scattering surfaces