Azimuthally dependent transmission loss and horizontal coherence in the presence of shelf internal waves

Abstract

A three-dimensional acoustic model, FOR3D, is used to propagate an acoustic field from a continuous wave point source to a horizontal array of receivers. The space–time variability of the continental shelf environment is modeled by shallow water of constant depth containing two types of internal waves: a spatially diffuse, randomly isotropic field, and a deterministically propagated, transversely invariant solitary wave packet. The internal wave packets cause azimuthal and range dependence in the properties of the acoustic signal as a function of (a) the bearing from the source, as referenced to the wave packet’s propagation vector, and (b) the location of the packet in the propagation path. The simulations also demonstrate a degree of out-of-plane scattering. Ensemble averaging is used to simulate horizontal coherence in environments containing combinations of the internal waves, and to illustrate the comparative importance of the diffuse and wave packet contributions. The cases studied here at selected frequencies between 100 and 400 Hz suggest that the performance of horizontal array receivers may require full three-dimensional modeling of propagation and media. [Work supported by the Office of Naval Research.]