Acoustic wave detection and analysis in a sandy sediment

Abstract

Coherence, wave front curvature, and direction of arrival provide important clues for analyzing acoustic signals in ocean sediments. Measurements were made using a buried acoustic receiving array and a mobile sound projector to study the underlying physical processes in the penetration of sound into sandy ocean sediments, particularly at shallow grazing angles, as part of the Sediment Acoustics Experiment (SAX99). The buried array was insonified by a wide-band sound source carried on a remotely operated vehicle (ROV). The discrimination between refraction and scattering processes was of particular interest. A method was used that employed coherent superposition to distinguish between refracted and scattered signals. Variable focusing was used to sharpen the distinction between refraction and scattering. Sound waves entering the sediment at steep angles were clearly refracted. At shallow angles, other processes come into play. This is a component of a multi-disciplinary effort to study sediment acoustics. [Work supported by ONR, Ocean Acoustics.]