SCATTERING FROM VERY ROUGH SURFACES BASED ON THE MODIFIED 2ND-ORDER KIRCHHOFF APPROXIMATION WITH ANGULAR AND PROPAGATION SHADOWING

A theory of scattering from very rough surfaces is presented. Both the surface rms height and the correlation distance are close to a wavelength and the rms slope is close to unity. The theory is based on the first-order and modified second-order Kirchhoff approximations. The second-order scattering includes the incident and scattering shadowing and the angular and propagation tapering shadowing. The angular shadowing limits the angular spectrum of the second-order scattering within those intercepted by the surface, while the propagation shadowing limits the propagation distance within those intercepted by the surface. The calculations are made for the rms height α/λ = 1.5, 1.0, and 0.5 and the correlation distance l/λ, = 1.8, and show close agreement with the Monte Carlo simulation of the exact integral equation. The results show that the first-order Kirchhoff scattering is dominant for α/λ = 0.5, but for α/λ =1.0 and 1.5, the second-order scattering becomes comparable to the first-order and produces the enhanced backscattering. Therefore, this theory provides a possible physical explanation for the enhancement. © 1990, Acoustical Society of America. All rights reserved.