Acoustic bottom penetration in a shallow water site from a parametric projector

Abstract

Acoustic penetration of a sandy ocean sediment by a narrow beam signal was investigated. A parametric source, the Simrad TOPAS, projected acoustic pulses at a shallow grazing angle into a sandy silt sediment in which a sparse 3-D array of acoustic sensors was buried, in a site off La Spezia, Italy. Although the experiment was conducted in shallow waters, the received signals were free of surface-bounce multipaths, due to the narrowness of sound beam, and excellent penetration was obtained. The collected signals were processed for direction and speed of the sediment acoustic waves. From a theoretical point of view, the medium is treated as a poroelastic solid governed by Biot’s theory of acoustic propagation. Comparisons are made between theory and experiment. [Work supported by Office of Naval Research, Ocean Acoustics Program, Code 321.]