ANALYSIS OF SCATTERING FROM ROUGH SURFACES AT LARGE INCIDENCE ANGLES USING A PERIODIC-SURFACE MOMENT METHOD

The moment method is used to calculate electromagnetic backscattering from one-dimensionally rough surfaces at near-grazing incidence (angle s of incidence up to 89 degrees). A periodic representation of the sca ttering surface is used to prevent edge effects in the calculated scat tering without the use of an artificial illumination weighting functio n. A set of universal series common to all elements of the moment inte raction matrix are derived that allow the efficient application of the moment method to the periodic surface. Comparison with other moment m ethod implementations demonstrates the efficiency of this approach. Th e scattering from surfaces with Gaussian roughness spectra is calculat ed at both horizontal and vertical polarizations, and the results are compared with the theoretical predictions of the small-perturbation me thod (SPM) and Kirchhoff approximation (KA). SPM shows the expected lo ss of accuracy in predicting the vertically polarized backscattering f rom small-roughness, short-correlation-length surfaces at large incide nce angles. SPM accurately predicts the backscattering from the same t ype of surface at incidence up to 89 degrees at horizontal polarizatio n. KA provides accurate estimates of the scattering from long-correlat ion-length surfaces as long as the incidence angle is small enough tha t surface self-shadowing does not occur. When shadowing occurs, KA sev erely underpredicts vertically polarized backscattering and less sever ely overpredicts backscattering at horizontal polarization.