Analysis of multipath time delay difference in deep ocean bottom bounce area and its application in near-surface target location

The bottom bounce areas in the first shadow zone in deep ocean are mostly contributed by four eigenrays including bottom-reflected path, surface-bottom-reflected path, bottom-surface-reflected path and surface-bottom-surface-reflected path, all of which arrive at different time with different time delay. On the basis of the time delay of four eigenrays, six arrival delay differences in deep ocean bottom bounce area can be obtained. As for a near-surface target source in deep ocean, six delay difference curves of eigenrays change approximately linearly with receiving depth. In this paper, the multipath arrival time delay structure of the bottom bounce areas in deep ocean is derived by the virtual source theory, and the approximate formulae of the time delay difference curves varying with the receiving depth are deduced. By analyzing the relationship between the time delay curves and the source range and depth, a method for source ranging and depth estimation in deep ocean bottom bounce area is proposed. The approach is demonstrated valid by the simulated data. Experimental results in the South China Sea show that when the transmitting and receiving distance is between 10 km and 30 km, the range and depth estimation results are in good agreement with the actual explosion range and depth, and the estimation error is less than 12%, which verifies the effectiveness of this method.