Sound speed and attenuation in marine sediments measured at high frequencies with a bottom probe system

Abstract

The evaluation of many high-frequency bottom-interaction models requires as inputs sound speed and attenuation in marine sediment. A bottom probe system mounted on the underside of a cable-controlled underwater vehicle was used to make measurements at 15, 30, and 60 kHz, and at probe depth positions of 17, 42, and 67 cm. Sound-speed ratios are determined in-situ to 0.1% and attenuation to 0.2 dB/m. Measurements made in a 1 km by 1 km area of Puget Sound indicated small but significant spatial distributions of acoustic properties in a nominally uniform area. Attenuation coefficients were determined using the empirical relation K times frequency to the nth power. Exponent n was approximately 0.70. Past data in a Santa Barbara area indicated an n value of 1.19. These results indicate that for different sediments, exponent n is distributed about one with significant deviations. [Work supported by Naval Sea Systems Command.]