ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2aUW11. Sound scattering at surface waves in the ocean, revisited.

Oleg A. Godin

NOAA/Atlantic Oceanographic and Meteorological Lab., 4301 Rickenbacker Cswy., Miami, FL 33149

In the absence of air bubbles, sound scattering at the ocean surface is usually considered to result from surface roughness in a steady homogeneous fluid. However, the roughness is a manifestation of surface waves and is inevitably accompanied by fluid motion in a subsurface layer. Being time and space dependent, these currents provide an additional physical mechanism of sound scattering. Although negligible in most cases because of the smallness of surface-wave frequency compared to sound frequency, scattering due to currents is shown to be significant at near-specular directions. The difference between results of the quasisteady (frozen medium) approximation and that of rigorous theory is pronounced in the latter case. A visual interpretation of the volume scattering enhancement in nearspecular directions and of failure of the quasisteady approximation to predict it is given. The effect of this additional scattering mechanism on the frequency spectrum of sound scattered at the ocean surface in deep and shallow water is analyzed. [Work supported by NRC.] [sup a)]On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.