Analysis of long-range sound propagation in West Pacific Ocean

Abstract

A long-range sound propagation experiment was conducted in the West Pacific Ocean in July 2013. LFM (Linear frequency-modulated) signals with frequency band of 260–360 Hz were transmitted by a transducer hung on a floating ship during the experiment and received by a horizontal line array towed by another ship sailing away from the transducer. Signals were received at the ranges 34–220 km, 612–635 km and 926–1029 km. In addition, explosives signals with explosive depth of 1000 m were received by a vertical line array and the maximum propagation range was 943 km. In this paper, experimental data on the long-range propagation are analyzed, and transmission losses versus range in convergence-zone propagation and those versus range and depth in deep-sound-channel propagation are obtained. The PE model and ray theory are used to analyze and explain the properties of the long-range pulse sound propagation observed in this experiment. It is shown that RAM is adequate for estimating the transmission loss. It is shown that in convergence-zone propagation water depth rarely influences the transmission loss when it is greater than the surface conjugate depth but contributes significantly to the transmission loss when the situation is the opposite, however the effect of water depth on transmission loss in deep-sound-channel propagation can be ignored. What’s more, the transmission loss increases when the distance between the receiver and the channel axis increases.