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

摘要

The solution of the integral equation for surface currentsrnat a perfectly conducting, smooth and gentle surface,rnwhen multiple scattering and surface shadowing can bernneglected, is presented. The diffraction corrections torngeometric optics (GO) values of the surface currentsrndepend on the local angle of incidence, surface curvaturesrnand their space derivatives. They were obtained up to thernsecond order of small parameter ~1/k, where k is the wavernnumber of the incident electromagnetic (EM) wave. It isrnshown that diffraction caused by the local surfacerncurvature results not only in small corrections to the GOrncurrents, but also gives rise to the surface currentrncomponents orthogonal to those induced by the incidentrnwave and obtained in the local GO limit. These currentrncomponents are responsible for backscattering into therncross-polarized EM waves, which is absent in the GOrnlimit. These general results are applied to the specific casernof microwave radio wave backscattering by the searnsurface described by the Elfouhaily power spectrum ofrnroughness, which allows obtaining the wind-speedrndependence of cross-polarization coefficients andrndiffraction corrections to backscattering cross sections.