Acoustic scattering from surfaces with high slope elements is modeled numerically by describing the surface as a conjoint assemblage of wedges. The impulse response of the surface is then obtained by adding the single wedge responses which are calculated from the Biot and Tolstoy solution [J. Acoust. Soc. Am.29,381–391 (1957)]. By use of the FFT the spectral description of the scattered field is obtained. This method is then applied to the study of mode interaction due to wall roughness in waveguide propagation [Research supported by ONR.]