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

4aUW5. Determining sediment absorption using ambient noise in shallow water.

Nicholas M. Carbone

Grant B. Deane

Michael J. Buckingham

Marine Physical Lab.-0238, Scripps Inst. of Oceanogr., 9500 Gilman Dr., La Jolla, CA 92093-0238

The ambient noise field in shallow water interacts strongly with the underlying seabed. As a consequence, the vertical directionality of the noise is largely determined from the characteristics of the seabed. In previous research, this property has been utilized to perform inversions for the compressional and shear wave speeds in hard seabeds. Soft seabeds predominate along continental shelf regions. In these cases, the absorption of compressional waves in the sediment is an important determinant of the noise field statistics which creates a measurable asymmetry in the vertical directionality. This asymmetry has been used as the basis of an inversion methodology, whereby the compressional wave absorption is estimated from measurements of the noise. The technique uses a broadband measurement from a vertically separated hydrophone pair at a fixed location. The ambient noise method yields an absorption estimate representing an average over range and depth. The technique represents a new means of estimating seabed absorption which leaves the sediment undisturbed. Absorption estimates obtained from inversions of ocean noise data taken above various soft seabeds will be presented. [Work supported by ONR.]