High-frequency model for sound transmission from an airborne source into the ocean

Abstract

The problem of the transmission of sound from an airborne source into the ocean, through the rough ocean surface, is considered. A high-frequency approximation is adopted, requiring for its validity that the sound wavelength in air be (much) less than typical radii of curvature and than typical displacements of the ocean surface. This condition is approximately met in many applications. Attention is focused on observation directions with small grazing angles. The result is approximately unaffected by surface roughness when the grazing angle is greater than the rms surface slope, and approaches a limit (proportional to the variance of the surface slope) when the grazing angle is less than the slope. The result is independent of the source height, under the stated approximations, as is also the case for the transmission through a plane surface. The enhancement due to surface roughness, even at moderate wind speed, ranges up to 10 dB. Subject Classification: [43]30.25.