Analysis of sound waves in a sandy sediment by focused array

The objective was to determine the underlying physical processes in the penetration of sound into sandy ocean sediments, particularly at shallow grazing angles. Signals were collected from a buried acoustic receiving array in a sandy sediment off the west coast of Florida, as part of the Sediment Acoustics Experiment (SAX99). The array was insonified by a wideband sound source carried on a remotely operated vehicle (ROV). The discrimination between refraction and scattering processes was of particular interest. To this end, an array-processing method was used that employed focusing to distinguish between refracted signals from a distant source and scattered signals from scatterers in the near field of the array. Sound waves entering the sediment at steep angles were clearly refracted. In the case of shallow grazing angles, the results were much more complicated. [Work supported by ONR, Ocean Acoustics.]