Underwater surveillance in a harbor is typically performed using active sonar systems. The performance of an active sonar can drastically change due to rapid variations in the sound propagation. This paper presents a method for detecting divers with open circuit breathing systems using passive acoustics. The authors have previously reported on a method for passive acoustic diver detection that employs two hydrophones. The proposed method uses a single hydrophone, resulting in a simpler and cheaper system. The method works by whitening the background noise and mitigating the influence of short-duration transients and rapid variations in the background noise. Results presented here show that the proposed algorithm performs better than the previous dual hydrophone method. Compared to the dual hydrophone method applied to the same frequency band, the proposed method achieves greater detection ranges at significantly lower false alarm rates. Pre-whitening permits us to use a wider analysis frequency band, resulting in further improvements to the detection range.

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In theory, a directional hearing device could apply large attenuation to a single noise source and achieve great enhancement of signal-to-noise ratio relative to an omni-directional device. However, as observed in many clinic studies, the actual benefit of a directional device measured in typical rooms rarely exceeds 6 dB, even in conditions with a single noise source located in the direction of maximum attenuation of the device. This dramatic reduction from the theoretical benefit is a manifestation of many factors, including mismatch in the microphone responses, misalignment of the device relative to the target source, head movement, head shadow, room reverberation, and so on. In the present study, we examine the relative contributions of these factors using computer simulations and electroacoustical measurements. The results provide a basis for setting realistic expectations of the benefit of directional devices for specific listening environments.