The bi-azimuthal scattering distribution of an abyssal hill

High-resolution bistatic images of a typical abyssal hill on the western fl ank of the Mid-Atlantic Ridge, are made with a low-frequency towed-array sy stem operating remotely at 1/2 convergence zone (similar to 33.3 km) stand- off. Comparison with modeled images, generated from high-resolution support ing bathymetry sampled at 5-m intervals, roughly the;wavelength scale, reve als that steep scarps return the strongest echoes because they project the largest area along the acoustic path from the source to receiver. Prominent returns deterministically image scarp morphology when the cross-range axis of the system's resolution footprint runs along the scarp axis. Statistica l fluctuations inherent in the scattered field prevent the system from dist inguishing; smaller-scale anomalies on the scarps, such as canyons and gull ies (similar to 100-200 m scale), that would otherwise be resolvable in ran ge, in certain bistatic geometries. The mean bi-azimuthal scattering distri butions of the two major scarps on the abyssal hill are identical and have strengths equal to the constant -17 dB +/- 8 dB. This suggests that long-ra nge reverberation from prominent geomorphological features of the world's m id-ocean ridges can be adequately modeled as Lambertian with-albedo pi/10(1 .7), given supporting bathymetry sampled with sufficient frequency to resol ve the projected area of these features. (C) 1999 Acoustical Society of Ame rica. [S0001-4966(99)01911-6].