Appraisal of an energy flux model for geoacoustic inversion of ambient noise coherence data

Abstract

The vertical directionality of the ambient noise field in a shallow-water waveguide is highly dependent on the local geoacoustic properties of the seabed and is directly related to the vertical noise coherence observed between two closely spaced hydrophones. As a result, a direct measurement of the broadband ambient noise coherence can be used to invert for sea-bottom properties that affect propagation. In previous work, an energy flux model [D. M. F. Chapman, Proc. Inst. Acoust. 9(4), 1–11 (1987)] for computing vertical noise coherence in shallow water was extended to include the effects of multilayered geoacoustic seabeds, refraction and absorption within the water column, sensor-pair tilt, and nondipolar radiation patterns due to near-surface but finite source depths. This modified flux-based coherence model was combined with a hybrid local/global nonlinear optimization scheme and used to estimate geoacoustic and source/sensor parameters for several synthetic data sets [F. Desharnais et al., J. Acoust. Soc. Am. 113, 2204 (2003)]. In this paper, the capability of the energy flux coherence model/geoacoustic inversion procedure is assessed for ambient noise data that were measured at several shallow-water sites over differing seabed types. Where possible, comparisons with geoacoustic properties estimated by other methods will be presented.