Geoacoustic inversion of noise coherence in shallow water

Abstract

It is known that the geoacoustic properties of a shallow-water sea-bed can be inferred from relatively simple measurements of the ambient noise coherence between a pair of vertically separated hydrophones [D. M. F. Chapman, ‘‘Surface-generated noise in shallow water: A model,’’ Proc. Inst. Acoust. 9, 1–11 (1987)]. The design of an autonomous buoy package for acquiring geoacoustic information by this method is currently being considered by DRDC-Atlantic in support of matched-field localization efforts that are being developed for use with rapidly deployable arrays. Initially, vertical coherence estimates from a simple shallow water noise model were fit to measured coherences by adjusting geoacoustic parameters by a trial and error procedure. A more systematic approach involves combining noise coherence models with nonlinear global optimization methods based on matched-coherence processing concepts to search the space of possible sea-bed parameters more efficiently. In this paper, we report on recent efforts to use a hybrid simplex simulated annealing scheme [M. R. Fallat and S. E. Dosso, ‘‘Geoacoustic inversion via local, global, and hybrid algorithms,’’ J. Acoust. Soc. Am. 105, 3219–3230 (1999)] to match an increasingly realistic suite of candidate geoacoustic parametrizations to some acoustic noise coherent data measured with modified sonobuoys deployed at several shallow water locations on the Scotian Shelf.