Investigations of marine mammal exposure to sound scattered from the sea surface.

Abstract

Scattering of sound from the rough sea surface results in variations in sound intensity. If the surface height variations are smooth, as they are during a swell, the surface can act as a concave mirror and amplify the sound intensity at its focal region. We have shown both analytically and using numerical modeling that the intensity at the focal region is a function of frequency: for a singly curved surface, the intensity at the focus varies linearly with frequency and for a doubly curved surface, this dependence is quadratic. Scattering of sound waves from a rough surface can also result in a reduction in intensity through dispersion. In this paper, we investigate the possible effects of exposure to sound scattered from the sea surface on marine mammals by computing the scintillation index as a function of range and depth for a variety of ocean environments, including those with surface ducts. We compute the scintillation index using a Monte Carlo technique, where for each surface height realization, we compute the scattered field in the waveguide exactly using the virtual source technique. We compute the Green’s functions needed in the virtual source technique using the Scooter propagation model.