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.

In this paper we compare the detection performance of underwater electric-field sensors against divers using three different detection algorithms (matched filter, non-coherent and quadrature detectors). The detection performance is quantified and presented as ROC-curves. The empirical results are based on measurements of signatures from divers with open circuit breathing systems. They were performed during two sea-trials in diverse environments. One site is a remote area with relatively low anthropogenic activity and the other site is a busy container terminal in the port of Gothenburg, both sites in Sweden.Of the three detectors evaluated, no single detector stands out. This may imply the usefulness of fusion as a means of improving the performance in the future. In Gothenburg harbor detection of divers can be performed at signal-to-noise ratios from -20 to 0 dB, depending on the noise situation. In addition to detection, it is found that it is possible to classify a contact as a diver.