ASA 126th Meeting Denver 1993 October 4-8

3aAO7. High-resolution backscatter from the Mid-Atlantic Ridge.

Nicholas C. Makris Jonathan M. Berkson Richard Menis

Naval Res. Lab., Washington, DC 20375

High-resolution backscatter is charted to respective scattering sites on the western flank of the Mid-Atlantic Ridge (MAR) by two-way travel-time analysis and beamforming. Since the range resolution of the low-frequency FM acoustic data is on the order of the acoustic wavelength (roughly 6 m), a bistatic mapping procedure is employed that accounts for bathymetric variation and combines calculations of eigenray paths and slant range to precisely locate scattering sites at ranges up to roughly one-half a convergence zone from the source/receiver. Right--left ambiguity of the horizontal-line-array data is resolved by taking advantage of the environmental symmetry-breaking properties of transmission loss, modeled with the parabolic equation, as well as by inversion of adjacent quasimonostatic observations. Mapped reverberation and estimated scattering strength are then projected onto high-resolution bathymetry for comparison. For the same scattering site and observation geometry, it is found that higher-resolution signals often yield higher and more localized scattering strength maxima. This suggests that discrete and spatially intermittent scatterers are important to reverberation in the MAR.