Deterministic reverberation from ocean ridges

Abstract

The deterministic relationship between low-frequency reverberation and detailed geomorphology is documented for wide-area insonifications of the western Mid-Atlantic Ridge. Charted reverberation registers precisely with extended ridges and has a high correlation with negative transmission loss, confirming previous analysis with lower resolution data [J. Acoust. Soc. Am. 95, 1865–1881 (1993)]. For a given ridge, prominent returns come from steep escarpments and cliffs that face the bistatic source and receiving arrays. This was hypothesized in the above reference, but could not be proven without the higher resolution waveforms and more sophisticated charting procedures of the present analysis. Monostatic and bistatic returns from the same lineated ridge at 1/2, 11/2, and 21/2 convergence-zone ranges are used to thoroughly document the registration with steep scarps. A decrease in resolution of the scattering site is also documented for increasing measurement range. Ambiguity from the horizontal receiving array is resolved by two independent methods that show close agreement for prominent returns. The first is an environmental symmetry breaking (ESB) technique that requires detailed knowledge of bathymetry to be incorporated into a range-dependent propagation model. The second is a global inversion of reverberation charts obtained from differing receiving-array locations and orientations. The global inversion requires no a priori environmental information and has not been previously applied to field data.