Characteristics of long-range sound propagation in western Pacific

Abstract

Acoustic signals can travel thousands of kilometers in seawater, and the characteristics of long-range sound propagation are different from short range propagation. This paper is based on a long-range underwater acoustic experimental data obtained from the western Pacific Ocean, where the farthest propagation distance is nearly 2000 km. The ocean environment information and vertical line array information are carefully processed. We analyze the attenuation of long-distance acoustic propagation in seawater and multi-path arrival structure characteristics under the complete acoustic channel environment of the ocean. In terms of the attenuation law of long-distance propagation energy, with the increase of propagation distance, the effect of seawater absorption on the attenuation of sound energy becomes prominent, and the selection of absorption coefficient is very important for the accurate prediction of sound field energy. Absorption in seawater of low frequency signals is small, and the transmission loss of acoustic signal with 100 Hz center frequency increases only by about 6 dB when the propagation distance increases from 1000 km to 2000 km. In terms of multi-path arrival structure characteristics of deep-sea acoustic channel for long-distance sound propagation, the thermocline sound velocity profile in the experimental sea area has a higher sound speed, making the number of eigenrays reaching the receiving point more and the multi-path arrival structure more complex. The arrival structure formed by sea surface reflected eigenrays is at the earlier position of the overall arrival structure and has relatively strong energy. Owing to the influence of subtropical water over the northwest Pacific Ocean on the sound speed profile, the time of some eigenrays arriving at the receiving point is earlier, and the length of multi-way arrival structure on the time axis is prolonged.