ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

1pAO13. The continuous spectrum and ambient noise inversions in shallow water.

Nicholas M. Carbone

Grant B. Deane

Michael J. Buckingham

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

It has been demonstrated that the ambient noise field in the ocean over continental shelf regions contains sufficient environmental information to allow for inversion of the geoacoustic parameters of the seabed. In past studies both compressional and shear wave speeds have been obtained which are in good agreement with measurements made using independent methods. Other factors which affect the coherence and influence the noise inversions for basement parameters include the sea state and sound-speed profile. We have observed that for low sea states, the ambient noise field contains little or no contribution from the continuous spectrum. Theoretical studies, on the other hand, indicate that the effect of the continuous spectrum is significant for soft seabeds. One explanation for its absence is that at low sea states there are few surface acoustic events close to the observation point, implying that the standard statistical model used to calculate the coherence is not valid for overhead sources. The density of surface acoustic sources in relation to the spatial structure of the ambient noise field will be explored. [Work supported by ONR.]