Experimental Demonstration of Shadow Zone Localization Using Deep Water Interference Patterns Measured by a Single Hydrophone

This paper discusses the frequency-range interference patterns of the sound field in deep water based on ray theory when the source and the receiver are near the sea surface. Approximate formulas of the frequency-range interference patterns in the shadow zone are derived. In the shadow zone, the sound intensity periodic structure is caused by the interference among the bottom-reflected, bottom-surface-reflected, surface-bottom-surface-reflected, and bottom-surface-reflected rays. The sound intensity changes according to the frequency with two cycles, which increase with the propagation range but decrease with the source and the receiver depths. As a result, the range and depth of the broadband sound source can be extracted from the interference cycles of the sound intensity using a single hydrophone. Interference patterns due to sea-surface broadband noise sources in the shadow zone have been observed in two deep-sea experiments in the South China Sea. Given the high signal-to-noise ratio, the interference cycles can be extracted manually from the time-frequency surfaces. Then, the availability of single hydrophone localization in the shadow zone is verified by experimental data. Compared with the conventional passive source localization methods, this method does not require broadband guide sources, precise seafloor acoustical parameters, or intensive computation of replica fields.