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