Modeling the temporal coherence of pulse propagation in shallow water with internal wave and rough boundary scattering

Abstract

For fixed source and receiver geometry, the broadband UMPE ocean acoustic model is used to make Monte Carlo predictions of pulse propagation in shallow water with internal wave and rough boundary scattering. The internal waves are modeled with a broad spectrum of excitation, and evolve slowly in geophysical time tg according to their intrinsic dynamics. For each realization of a field of internal wave fluctuations, assumed frozen at time tg, a time series of complex demodulates of the received acoustic signal is computed by Fourier synthesis. The square modulus of this function yields the intensity envelope time series, A(t), and many peaks of A(t) correspond to ray arrivals and travel times that are spread by scattering. By advancing tg and repeating the pulse transmission simulation, the function A(t,tg) is computed and displayed as a ‘‘waterfall’’ plot. Examination of these plots gives quantitative information about the temporal stability and coherence of multipath arrivals in shallow water. Examples are presented in three distinct geographical areas: Florida Strait, New Jersey Shelf, and the Yellow Sea. [Work supported by ONR.]