Small perturbation method of high-frequency bistatic volume scattering from marine sediments

The first-order small perturbation method (Born approximation), as frequent ly applied to high-frequency scattering from marine sediments, is criticall y reviewed, tested for accuracy, and extended. The sediment is modeled as a n acoustic-fluid half space with random fluctuations in density and compres sibility. Several cases of volume scattering from typical marine sand and m ud sediments are presented to illustrate the effects of two important assum ptions: 1) the effects of assuming the density and compressibility fluctuat ions are proportional, and 2) half-space effects, By relaxing the assumptio n that the sediment density and compressibility are proportional, the bista tic scattering cross section is significantly altered. The effects of prope rly modeling the sediment as a random half space (as opposed to an infinite continuum) are also discussed. In the context of first-order perturbation theory, half-space effects manifest themselves as a "modified" spectra for density and compressibility fluctuations. It is shown that, for Iossy sedim ents and for scattering near the specular direction, half-space effects are significant and cannot be neglected. This result is significant because cu rrent models of sediment volume scattering do not include half-space effect s. In addition to the theoretical model, exact numerical simulations are us ed to evaluate the accuracy of the perturbation model for a limited number of cases.