ASA 127th Meeting M.I.T. 1994 June 6-10

1pAO5. High-resolution sonar volume scattering and attenuation measurements in marine sediment.

Lester R. LeBlanc

Steven G. Schock

Darryl L. DeBruin

Lachlan I. Munro

Ctr. for Acoust. and Vib., Dept. of Ocean Eng., Florida Atlantic Univ., Boca Raton, FL 33431-0991

This paper examines the use of normal incidence high-resolution sonar for seafloor sediment classification. Volume scattering, a measure of the scattering strength per cubic meter, and attenuation measurements taken at several sites are compared to the acoustic characteristics of cored sediments. A relaxation time model utilizes the shift in the center frequency of acoustic reflections from within the sediment to measure attenuation. Using a statistical model to detect sediment transition layers, volume scattering and attenuation values are calculated between detected layers. The scattered energy measurements reveal two separate probability density functions. The probability density of scattering from layer boundaries is characterized by a Rayleigh density function whereas volume back scattering is characterized by an exponential density function. When the measured volume scattering coefficient is compared to sediment properties, generally, sediments with large grain components produce larger volume scattering coefficients. In comparing attenuation measurements with sediment types, sands attenuate acoustic energy more rapidly than clays and silts. By combining sediment volume scattering measurements, attenuation measurements, and detected layer impedance profiles, it is expected that in situ acoustic classification of marine sediments will become more viable. [Work supported by ONR.]