Three-dimensional sound propagation and scattering in an ocean with surface and internal waves over range-dependent seafloor

Abstract

Underwater sound propagation in an oceanic waveguide can be influenced by environmental fluctuations on the boundaries at the sea surface and the sea floor and also in the ocean interior. These fluctuations can in fact cause three-dimensional acoustic propagation and scattering effects, especially when the horizontal/azimuthal gradients of the fluctuations are significant. Many studies have only been considering individual environmental factor, but the current work presented in this talk is investigating the joint effects by surface and internal waves over range-dependent seafloor consisting of sand waves, ripples, or scours. This scenario represents better the reality in some dynamic areas on the edge of continental shelf (shelfbreak), continental slopes, submarine canyons, and also riverine and estuarine environments. Two research methods are taken here: one is theoretical analysis utilizing acoustic mode theory, and the other is numerical modeling with three-dimensional parabolic-equation models. The frequency dependency of the joint effects will be analyzed, as well as the dependencies on the source and receiver positions, acoustic mode numbers, and/or ray angles. Numerical examples of underwater sound propagation and scattering with realistic environmental conditions will be presented with statistical analysis on the temporal and spatial variability. [Work supported by ONR.]