ASA 127th Meeting M.I.T. 1994 June 6-10

1pUW10. Wide-area backscatter from the Mid-Atlantic Ridge experiment of 1993.

Nicholas C. Makris

Lilimar Avelino

Richard Menis

Naval Res. Lab., Washington, DC 20375

The goal of the Main Acoustics Experiment of 1993 (MAE) is to reveal the fundamental scattering process responsible for long-range reverberation. The initial objective is to compare reverberation and geology measured at specific sites of morphology characteristic to the Mid-Atlantic Ridge. Previous analysis of data from the Acoustic Reconnaissance Cruise of 1991 (ARC) shows a high correlation between spatial charts of measured backscatter and modeled transmission loss (TL). Specifically, measured backscatter maxima correspond to modeled TL minima. These extrema are typically charted to ridges that protrude above the excess depth contour along scarps facing the observation and are most pronounced at n+1/2 convergence zone (CZ) ranges. Charted MAE backscatter shows similar behavior and the expected dependence upon TL. At least 50% of spatial variations in charted backscatter can be accounted for by TL. To properly register discrete backscatter returns with geomorphology, ambiguity in the towed-array data is eliminated by two independent techniques. The first optimally combines redundant backscatter observations made with differing array orientations to eliminate line-array ambiguity. This is possible because MAE tow-ship tracks were designed with ambiguity resolution as an essential theme. The second uses environmental symmetry breaking information available in modeled TL to resolve ambiguity.