ASA 126th Meeting Denver 1993 October 4-8

5aUW4. Modeling acoustic particle velocity in range-dependent environments with a parabolic equation code.

K. B. Smith G. L. D'Spain W. S. Hodgkiss

Marine Phys. Lab., Scripps Inst. of Oceanogr., San Diego, CA 92152-6400

Measurements have been made of the acoustic particle velocity field generated by a towed source transmitting 7-, 10-, and 16-Hz tones. The periodic change in the polarization of the motion as a function of source--receiver range, from prograde circular motion to retrograde circular motion and back, appears to have been disrupted by changes in slope of the bottom topographic features in the experiment. In order to test this hypothesis, the University of Miami parabolic equation code (UMPE) was modified in order to efficiently calculate acoustic particle velocity. This numerical code makes effective use of the equivalent fluid approximation for low shear speed ocean bottoms [C. T. Tindle and Z. Y. Zhang, J. Acoust. Soc. Am. 91, 3248--3256 (1992)]. The predictions of the UMPE model are compared with the actual measurements, and with the predictions made by the finite element parabolic equation (FEPE) by M. D. Collins, which explicitly incorporates the effects of bottom shear. [Work supported by ONR.]