Studies of shallow-water acoustic coherence using the modal phase structure function

Abstract

The modal phase structure function, defined by the cross correlation of the phase for any given mode at two different points in space, time, or frequency, can provide some useful insights into the physics of array coherence in shallow water. Using this indicator of the acoustic field coherence, as well as the usual 〈pp*〉 definition, we examine the coherence of acoustic signals in the 10-to-1000-Hz range scattered by both bottom and water column inhomogeneities. In previous work (Sperry, Ph.D. thesis, 1999), we emphasized large-scale water column inhomogeneities, and ignored some of the finer scale ocean phenomena that could cause significant mode coupling. In this work, we address both phenomena and the general issue of mode coupling. In particular, we address the soliton field in the water column and small-scale inhomogeneities in the bottom sediments. Water column environmental data from the PRIMER experiment and bottom environmental data from the STRATAFORM experiment are used to guide our analyses. Results are compared to acoustic observations for the PRIMER experiment, where both acoustic and environmental data were gathered simultaneously. [Work supported by ONR.]