Three-dimensional acoustic modeling of a complex harbor environment

Abstract

Typically, we model sound propagation in the ocean viewing it as an “open” environment where the sound propagates outwards from the source. Of course, targets are reflectors, and other features such as islands and seamounts have been of interest as false targets. However, the standard acoustic models based on rays, normal modes, spectral integrals, and parabolic equations generally consider outgoing energy confined to a single bearing line. In contrast, constrained or partially closed environments such as harbors introduce special issues. Obviously, the sound can be reflected back by seawalls and ship hulls, to mention just a couple of features of harbors environments. Considering coastal environments more broadly, sound reflections also may be caused by wharves, docks, piers, boat landings, quays, floats, groins, and jetties as well as natural features such as submarine canyons. In short, we have sound refracted in the latitude/longitude plane and reflected by a variety of features. In terms of computational ocean acoustics there are few options for modeling such problems. We discuss a comprehensive 3D beam tracing approach implemented in a model called BELLHOP3D that can handle 3D effects including complete reversal of the sound. It is also capable of handling narrowband waveforms (tonals) as well as full broadband timeseries. We will demonstrate and test the model using an example location that is expected to become the site of a future sea test.