Broadband frequency dispersion prediction using shallow-water data from Tanner Bank

Abstract

Recent analyses of explosive charge reverberation and echo data [Davies etal. (1994)] showed a useful active broadband dispersion phenomena that was observed empirically in measured data for propagation paths within a mixed layer (ML). This Wilson Dispersion Phenomena (WDP) was originally noted in an environment which was characterized by a mixed layer. In April, 1994 an experiment [Holland etal. (1994)] was conducted under Navy sponsorship off the coast of California (Tanner Bank) in order to examine low-frequency active acoustic sources for use in characterizing bottom parameters in shallow water. This data set provided an ideal scenario for further examination of WDP. Upon preliminary examination of the Tanner Bank data set, the WDP was found to not only exist, but also to be predominant in environmental scenarios other than in the presence of a mixed layer. The phenomena proves to be highly dependent upon source–receiver geometry and environmental acoustic (EVA) characteristics such as sound-speed structure, bathymetry, bottom sediments, etc. It has been shown using the Tanner Bank data set that the occurrence of this phenomena can be modeled to a reasonable degree of accuracy using a time domain finite element parabolic equation model and a normal mode model. [Work supported by ONR.]