Comparison of low-frequency acoustic backscatter data with model predictions using fine-scale geomorphology

Reverberation data were collected over the western flank of the Mid-Atlantic Ridge during the Acoustic Reverberation Special Research Program (ARSRP) cruises of 1991 and 1993. The site of the experiments included regions of large sedimented ponds and regions of large ridges of exposed rock with relief of 500 m in several miles. High-resolution bathymetry surveyed in the summer of 1992 and gridded to 200 m provided the geomorphology (i.e., bathymetry, slope, and slope bearing) with local slopes reaching 30°. Finer scale local bathymetric surveys in 1993 revealed higher sloped scarps, some of which were vertical. The reverberation data showed numerous highlights, suggesting the possibility of facet scatter from some of these scarps. The reverberation data, when smoothed to resolutions of several hundred meters, could be successfully modeled using a formulation of Lambert’s law with local grazing angle as the argument of the sine squared and the 200-m bathymetry providing the local slopes and slope bearings. The Lambert coefficient was found to vary over the region with dB values of −27 in sedimented regions and −17 in exposed rock regions. [This work is supported by the Office of Naval Research.]