Experimental and Theoretical Study on Arrival Times and Effective Velocities in the Case of Long-Range Propagation of Acoustical Pulses Along the Shelf Edge in a Shallow Sea

An experimental study aimed at the measurement of arrival times and effective velocities of acoustical pulses propagating approximately along the edge of the continental shelf was conducted in the Sea of Japan in early autumn. In a posteriori theoretical analysis and modeling of sound propagation in this experiment modal structure of acoustical field along the path was described and a number of general conclusions on the formation of such fields in course of sound propagation over distances of tens and hundreds of kilometers were formulated. An algorithm for predicting effective velocities of long-range propagation of acoustical pulses in shallow water was developed on the basis of these conclusions. The algorithm is based on the averaging of group velocities of the first modal component of the pulse over the entire track. It was shown that on the considered path of approximately 136 kilometers horizontal refraction is one of the major factors contributing to the dispersion of pulsed signals. This effect also causes additional delays as compared to the sound propagation along the respective geodesic path on the Earth's surface. Implications of the importance of taking the horizontal refraction into account in estimation of arrival times in the modeling of long-range propagation and the solution of acoustical ranging problems are also discussed.