ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

4aUW7. Acoustic bottom penetration in a shallow water site from a parametric projector.

Nicholas P. Chotiros

Adrienne M. Mautner

Appl. Res. Labs., Univ. of Texas, P.O. Box 8029, Austin, TX 78713-8029

(Angstrom)ge Kristensen

Oddbjorn Bergem

Arne Lovik

SACLANT Undersea Res. Ctr., 19026 La Spezia, Italy

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.]