THEORETICAL ANALYSIS OF THE BOUNDARY REFLECTION LOSS AND THE PARAMETER EXTRACTION AT SMALL GRAZING ANGLES

It has been shown that for "high speed" sediment the effects of layered structure of the sediment are not significant for a certain range of frequency at small grazing angles, and the reflection behavior approaches to the Eayleigh reflection specified by the surficial sediment parameters （ρ,c,a）. In that case, if the absorption frequency relation given by Hamilton is considered, then the reflection loss will be frequency independent. So the frequency dependence of the real reflection loss is not due to the layered structure but the scattering of the surface roughness. If the scattering loss is considered by using Bass' perturbation theory, the reflection loss at small grazing angles can be written as:
where Q₀ is the term due to Eayleigh loss independing on frequency, Q₁ is the term due to scattering depending on frequency f and the roughness parameter σ. It is found, that in the frequency range of （0.5-3.0 kHz） not only the magnitude but also the tendency of variation of the parameter Q extracted from different experiments are distributed in the permissible region predicted by the theoretical model.