ASA 125th Meeting Ottawa 1993 May

3aUW8. Inverting, imaging, and mapping ocean-basin reverberation onto high-resolution bathymetry.

Nicholas C. Makris

Jonathan M. Berkson

Naval Res. Lab., Washington, DC 20375

The objective of this paper is to determine the relationship between low-frequency ocean-basin reverberation and bathymetry. Long-range reverberation data acquired on the western flank of the Mid-Atlantic Ridge (MAR) are mapped onto high-resolution bathymetry. Since reverberation was measured via horizontally towed line array, there is a ``right--left'' ambiguity about the array's axis and a decrease in resolution for off broadside beams and more distant returns. These ambiguities make an objective correlation between reverberation and bathymetry difficult. Therefore, an optimization procedure has been applied for eliminating the right--left ambiguity and maximizing resolution by simultaneously inverting data taken with differing array locations and orientations. Combined with range-dependent propagation modeling, the images show that distant reverberation is significant when the intermediate propagation path is free from bottom interaction. Since the experiment site is primarily bottom-limited, such paths are not abundant, and a sparse azimuthal distribution of strong returns at convergence zone intervals is often found. In general, strong returns coincide with prominent bathymetric features, such as abyssal hillsides. However, such correlations must be made judiciously because the azimuthal resolution of distant returns is often on the order of the width and separation between ridges in the MAR's continuously rugged bathymetry.