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

5pUW8. Analysis of a bottom backscattering data set: Evidence of sub-bottom volume scattering.

Charles W. Holland

Peter D. Neumann

Planning Systems, Inc., 7923 Jones Branch Dr., McLean, VA 22102

Low-frequency (under 1 kHz), low-grazing angle (under 30(degrees)) bottom backscatter data from the Messina Cone in the Ionian Sea are analyzed. Core data and bottom loss data both indicate that the sediment impedance at the water--sediment interface is too small to attribute the observed backscatter to rough surface scattering. It is hypothesized that the scattering arises from lateral discontinuities of turbidite layers in the sub-bottom volume. A self-consistent acoustic and geoacoustic model for treating such sub-bottom volume inhomogeneities is proposed and compared with the measured data. The model appears to successfully predict the grazing angle, frequency, and pulse length dependence of the measured data. The pulse length dependence of the measured data is hypothesized to arise from the lateral size distribution of the discontinuities. Thus the pulse length dependence of bottom scattering could be a useful measure of the lateral length scales of sub-bottom volume inhomogeneities. [Work supported by ONR/AEAS.]