MICROWAVE BACKSCATTERING FROM THE SEA SURFACE:DIFFRACTION CORRECTIONS TO THE KIRCHHOFF APPROXIMATION

摘要

The solution of the integral equation for surface currents at a perfectly conducting, smooth and gentle surface, when multiple scattering and surface shadowing can be neglected, is presented. The diffraction corrections to geometric optics (GO) values of the surface currents depend on the local angle of incidence, surface curvatures and their space derivatives. They were obtained up to the second order of small parameter ～1/k, where k is the wave number of the incident electromagnetic (EM) wave. It is shown that diffraction caused by the local surface curvature results not only in small corrections to the GO currents, but also gives rise to the surface current components orthogonal to those induced by the incident wave and obtained in the local GO limit. These current components are responsible for backscattering into the cross-polarized EM waves, which is absent in the GO limit. These general results are applied to the specific case of microwave radio wave backscattering by the sea surface described by the Elfouhaily power spectrum of roughness, which allows obtaining the wind-speed dependence of cross-polarization coefficients and diffraction corrections to backscattering cross sections.