Seafloor acoustic backscattering from different geological provinces in the Atlantic Natural Laboratory
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The characteristics of acoustic signals backscattered from inside-corner and outside-corner oceanic crust are investigated using acoustic reverberation data from the 1993 Acoustic Reverberation Special Research Program (ARSRP) Acoustics Cruise. Specifically, the seafloor dip distribution, as measured from Hydrosweep bathymetry data is compared in areas of each crustal type and a correlation between seafloor dip and seafloor scattering strength is sought. Beamformed and match-filtered acoustic data from the site A (run 1) monostatic, wideband, LFM (linear frequency modulated) experiment are used to find the scattering strength corresponding to specific areas of the seafloor. Scattering strength is determined as the average of intersecting beams from different source locations in order to reduce the left-right ambiguity inherent in beamsteering of a linear array. When overlaid on the bathymetry map, high-scattering strengths are found to correspond to steep flanks of seafloor features and can be used to determine their shape and orientation. Some of these feature shapes are characteristic of specific crustal regions. Cross-plotting scattering strength with true grazing angle or seafloor dip shows a trend increasing at a rate of about 0.1 dB/deg. This trend is not, however, sufficiently constrained to be a useful predictor. It is concluded that the seafloor dip, on the scale of a few hundreds of meters, that can be resolved with Hydrosweep bathymetry data, influences but does not determine, scattering strength. Since, in detail, the observed variations in scattering strength are larger than can be explained by data error or seafloor dip, it is suggested that other characteristics of steeply dipping areas, such as subsurface properties or smaller scale surface features, strongly affect the level of backscattered signals. (C) 1997 Acoustical Society of America.