3aUW10. Mode coupling analysis for a resonance effect due to an internal soliton.

Session: Wednesday Morning, May 15

Time: 10:50

Author: Michael K. Broadhead
Author: Robert L. Field
Location: Code 7173, Naval Res. Lab., Stennis Space Center, MS 39529-5004


As pointed out by Zhou et al. [J. Acoust. Soc. Am. 90, 2042--2054 (1991)], nonlinear shallow-water solitary internal waves (SIW's) can enhance the bottom interaction of underwater sound. For a lossy ocean bottom, this has the effect of a level change (in addition to fluctuations) in the transmission loss at preferred frequencies. The mechanism for this effect is acoustic mode coupling due to the depression of higher sound-speed water into lower speed water (at the pycnocline). It is also possible for this mechanism to induce a transfer of acoustic energy from below the thermocline into the mixed layer, as has been shown elsewhere, where a two-layer pycnocline/sound-speed environment was used, along with a KdV soliton. Over the frequency range studied (900--1030 Hz), the energy transfer spectrum exhibited a doublet resonant structure. It was also found that an increase in the SIW length scale was accompanied by a positive shift in the resonant frequencies. A simple model is offered that qualitatively accounts for these two features which is based on mode coupling theory. Also presented is the dependency of the resonance frequencies on the sound speeds and layer thicknesses of the acoustic environment.

from ASA 131st Meeting, Indianapolis, May 1996