ASA 125th Meeting Ottawa 1993 May

4pUW3. The effect of frequency-dependent bottom reflectivity on transmission loss in shallow water over a sandy bottom.

J. Matthew Tattersall

Dmitry Chizhik

Bernard F. Cole

Naval Undersea Warfare Ctr., New London CT 06320

F. R. DiNapoli

SAIC, New London, CT 06320

The effect of frequency dependence of bottom reflectivity on acoustic transmission in shallow water over a sandy bottom is investigated using transmission loss data from measurements conducted at a wide range of frequencies. Biot's theory of acoustic wave propagation in fluid-saturated porous media is applied to prediction of bottom reflectivity for a sea bottom consisting of medium grain size sand. For a homogeneous half-space the theory predicts a frequency-dependent bottom reflectivity in contrast to the fluid or solid bottom models. Transmission loss predicted using the Biot model of the sediment shows agreement with measurements at all frequencies considered, which ranged from 100 to 8000 Hz. The fluid model, which assumed a dispersionless velocity and an attenuation that is proportional to frequency, has performed poorly at the low frequency of 100 Hz. [Work supported by Naval Sea Systems Command 06UR1.]