A time-domain path integral method for analyzing reflections from a rough sea surface

Abstract

Recently, experimental data were gathered for broadband (500 Hz–20 kHz) sound transmissions in shallow water over a period of seven days. The processed data form a good approximation to the impulse response of the environment, including direct signal paths, surface interactions, and bottom interactions, from a source to both local and remote receivers. Since the signals resulting from a single interaction with the ocean surface can be cleanly separated from other arrivals, these signals become a rich source of information about surface wave motion and thus about the state of the sea. To analyze the effects of surface waves (surface wave height, period, wave number, wave direction) on the received signal, including frequency dependence, a tool for efficiently calculating broadband response of a rough sea is needed. Instead of solving for the wave field at many frequencies and synthesizing the result into a broadband response using Fourier techniques, a direct computation of the response uses raylike techniques to sum over all significant paths in the time domain. For some problems, this technique is much more efficient than frequency-domain approaches such as PE or wave number integration, while providing the low-frequency accuracy that is only approximated by ray theory approaches. [Work supported by ONR.]