Acoustic backscattering at low grazing angles from the ocean bottom. I. Bottom backscattering strength

Acoustic backscattering measurements on a sand bottom were made at grazing angles in the range of about 2°–10° in water depth of approximately 15.5 m near San Diego, CA [T. G. Goldsberry, S. P. Pitt, and R. A. Lamb, J. Acoust. Soc. Am. Suppl. 1 72, S74 (1982)]. Data from these measurements have been analyzed to determine the mean value and standard deviation of the bottom backscattering strength per m2 as a function of grazing angle, insonified area, transmit signal type, and frequency. A curved ray path propagation model and measured sound speed profiles were used to determine grazing angle versus time. The mean value followed Lambert's law for the range of grazing angles measured and for all frequencies used. No significant differences in mean value were observed when the insonified area and transmit signal type were varied. The observed frequency dependence of the bottom backscattering strength per m2 falls in the range from f1.5 to f1.8 for this relatively flat, sandy bottom. [Work supported by NAVSEA 63R and NORDA Code 113.]