Inversion of broadband ambient noise in shallow water for the geoacoustic parameters of the seabed

Ambient noise propagates through the ocean in much the same way as sound from a man‐made source. The noise is a stochastic phenomenon, but some of its statistical measures, for instance, the spatial coherence, may be influenced by the environment in a systematic and stable manner. Such statistical measures may then be inverted to obtain information on the environment. In particular, over the continental shelf, where water depths are less than 200 m, the nature of the seabed has a significant effect on the vertical coherence, or, equivalently, vertical directionality, of the noise in the water column. This suggests that simple measurements of the vertical coherence of the noise, taken with just two hydrophones in the water column, may be inverted to yield the geoacoustic parameters of the bottom. An essential element of such an inversion procedure is an ambient noise model which includes a geoacoustic model of the sediment. In the presentation, a noise inversion model based on spatial coherence will be described. Examples of inversions for the bottom properties, obtained from real data taken at shallow‐water sites in the northern and southern hemispheres, will be presented. [Research supported by ONR.]