ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pUW6. Acoustic interaction with a propagating internal soliton wave packet in shallow water.

Michael K. Broadhead

Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004

One-way ocean acoustic propagation through shallow water internal waves was numerically simulated, where the oceanographic model consisted of a two-layer density/temperature stratified fluid overlying flat bathymetry. For sufficiently small amplitudes in a lossless medium, shallow water internal waves are governed by the Korteweg--de Vries (KdV) equation, which possesses soliton solutions. A finite difference scheme was used to numerically time evolve initial conditions, the details of which determine the number and properties of the soliton events that emerge. The internal waves (in a center-of-mass frame) were introduced through the index of refraction in the acoustic wave equation. Range-dependent normal mode and PE models were used to compute transaction-loss for various frequencies (100 Hz--10 kHz), for different times during the soliton wave packet evolution, and for different initial conditions. For lower frequencies, refraction effects caused an increase in the mean TL level due to increased bottom interaction, while for higher frequencies, the predominant effect was spatial/temporal fluctuations and the enhancement of surface duct propagation. Dispersive terms exist for all but special initial conditions, but their amplitudes were generally too low to be significant. [Supported by Office of Naval Research and Naval Research Laboratory.]