Comparison of ocean-acoustic horizontal coherence predicted by path-integral approximations and parabolic-equation simulation results

Abstract

A line-integral approximation to the acoustic path integral has been used to generate predictions for the characteristic length scale of horizontal, cross-range coherence in long-range ocean-acoustic propagation. These estimates utilize a single range-independent sound-speed profile and the mean variance, as a function of depth, of fractional sound-speed perturbations due to internal waves. The length scales predicted by the integral approximation have been compared to the values generated by parabolic-equation simulations through multiple realizations of Garrett-Munk internal waves. One of the simulation environments approximates the Slice89 experiment; transmissions from a 250-Hz source were simulated in a deep-water transect to a maximum range of 1000km. The second environment corresponds to one of the propagation paths in the North Pacific Acoustic Laboratory (NPAL) experiment. The source in this experiment was bottom-mounted near Kauai, Hawaii and the relevant receiver consisted of five vertical line arrays oriented transverse to the propagation path with cross-range separations ranging from approximately 500 to 3500m. The receiver was at a range of 3889.8km from the source. The predicted length scales are consistently shorter than the parabolic-equation results by 30%–80%, depending on the range and environment examined.