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