Azimuthal and depth-dependent transmission loss caused by shelf internal waves

Abstract

The amplitude of an acoustic field propagating through a stratified continental shelf water column in the presence of internal wave packets is shown to be azimuthally and depth dependent when referenced to the propagation vector of the internal wave packet. Internal wave (IW) packets, which propagate across the continental shelf, are known to be regularly generated each tidal cycle at the shelf break edge in stratified water column conditions. They are dispersive in nature and change in physical structure as they propagate away from the generation site. Their wave directional spectrum is highly peaked. Consequently, the wave-number spectrum of the continental shelf sound velocity field is highly directional and will be shown to cause azimuthal dependency in the properties of the acoustic field as a function of range and bearing from the source. Preliminary results of numerical solutions to the parabolic equation approximation of the Helmholtz equation are presented to substantiate the above assertions, in particular for propagation through a uniform internal wave field of a fixed wave number and amplitude. [Work supported by the Office of Naval Research.]