Incoherent ocean bottom scattering from non-Gaussian slopes in the Pacific.

Abstract

Kirchhoff scattering theory was applied to measurements of bottom scatter to explain the time and angle spread of signals received on a horizontal array. The data were collected during ‘‘Pacific Echo II,’’ a joint experiment conducted by the U.S. Naval Research Laboratory and the Canadian Defence Research Establishment Pacific. Source signals were standard MK-61 SUS charges detonated at 244-m depth. The array was 300 m long, towed at 4 kn and 200-m depth. The 64 hydrophone groups of the array were equally spaced. The site was characterized by an average sediment thickness of 25 m. Water depth was 5000 m permitting time separation of arrivals having different numbers of bottom bounces. A slope density function was constructed partially from seabeam measurements at the site and partially from documented deeptow measurements at other Pacific thin sediment sites. Predictions of omni- and beam-formed time series and an angle spread function were calculated and compared with the data. Results show that the observed long coda and large angle spreads may be predicted by the long non-Gaussian tails of the slope density function.