Improved passive acoustic detection of divers in harbor environments using pre-whitening

Abstract

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.

An Approach for Diver Passive Detection Based on the Established Model of Breathing Sound Emission

“…The reason for this is that the noise reduction process further enhances the SNR of 13 kHz-18 kHz band signal. The ESD method detects the diver to a maximum range of near 20 m, which is similar to the detection results of Johansson [6]. Compared with that, the BIED method can detect diver until the 40 m range.…”

“…Previous research has shown that frequency sub-band envelope spectrum detection (ESD) is an effective detection method to detect the presence of diver [3,6]. ESD takes D env as the feature of the diver's breathing sound, where D env denotes envelope spectrum energy in the range of typical human breathing rates 0.3 Hz-1 Hz.…”

“…Assuming noise power is known and is δ 2 , γ is the posterior SNR which is given as γ kl = Y 2 (k, l)/δ 2 . Equation (6) demonstrates that the denoising performance of the α is related to block size L B and threshold level λ. Because pure reference signal Y pure is unknown, the Stein unbiased risk estimation (SURE) [21] algorithm is used to estimate risk equation given as [16]…”

“…Ref. [6] pre-whiten the noise and detect the diver based on envelope spectrum to a maximum range of 20 m. Although the sounds can be spatially filtered using an underwater array [7], we focus on detecting the presence of diver in a single channel, which also can be used in the multichannel scene.…”

Partial dereverberation used to characterize open circuit scuba diver signatures

“…Extensive work in the same estuarine environment was conducted by Stolkin et al (2006), Stolkin and Florescu (2007), Bunin et al (2007), Borowski et al (2008), and , giving detection distance of more than 100 m for single hydrophone using a noncoherent envelope processor. Lennartsson et al (2009), Johansson et al (2010), and Lennartsson et al (2010) conducted several sea trials with single hydrophones, a six hydrophone array, and electric underwater sensors. Detection distances for the port of Gothenburg (Sweden) were on the order of 30 m for a single hydrophone.…”