Seafloor acoustic backscattering from different geological provinces in the Atlantic Natural Laboratory.

Abstract

The characteristics of acoustic signals backscattered from inside‐corner oceanic crust and outside‐corner crust are investigated using acoustic reverberation data from the 1993 ARSRP Acoustics Cruise. Specifically, the seafloor dip distribution is compared between areas of each crustal type and correlations are sought between true grazing angle and backscattered signal strength. Beamformed and match filtered acoustic data from the monostatic, wideband, LFM experiment at Site A are used to find the scattering strength corresponding to specific areas of the seafloor. Scattering strength determined from intersecting beams of different segments are summed to reduce left–right ambiguity. At the scale of analysis, high scattering strengths are found to correspond to steep flanks of seafloor features and can be used to map their shape and orientation. Some of these features are characteristic of specific crustal regions. Scattering strength is found to increase with increasing effective grazing angle at a rate of about 0.1±0.01 dB/degree. However dip values are so scattered that the seafloor dip, on the scale of a few hundred meters cannot be used to predict backscatter intensity. Some other characteristics of steeply dipping areas, such as subsurface heterogeneities or smaller scale surface features, strongly influence the level of backscattered signals. [Work supported by ONR.]