Near and Far-Field Acoustic Scattering through and from Two Dimensional Fluid-Fluid Rough Interfaces

摘要

Modeling the ocean as a homogenous fluid and the sediment as a lossy homogenousfluid, computer simulations of these experiments based on analytical derivations in this work show that roughness of the water-sediment interface causes propagation of acoustical energy from water into the sediment at grazing angles below the compressional critical grazing angle; these simulations indicate that the experimental results can be explained in terms of diffraction of an ordinary longitudinal wave. These simulations use an analytical expression for the time-dependent mean square incoherent field scattered through (and from) a rough 2-D fluid-fluid interface that is derived in terms of the bistatic scattering cross section per unit area per unit solid area (differential cross section) of the rough interface. First-order perturbation theory is used to derive an expression for the differential cross section. The coherent field is calculated using the flat-surface result (zero-order perturbation theory) and compared to the coherent component of the second-order perturbation theory result. Effects of sound-speed gradients on the field scattered from the rough water-sediment interface are also shown using the first-order perturbation derivations.