Abstract
Anthropogenic impulsive sound sources with high intensity are a threat to marine life and it is crucial to keep them under control to preserve the biodiversity of marine ecosystems. Underwater explosions are one of the representatives of these impulsive sound sources, and existing detection techniques are generally based on monitoring the pressure level as well as some frequency-related features. In this paper, we propose a complementary approach to the underwater explosion detection problem through assessing the arrow of time. The arrow of time of the pressure waves coming from underwater explosions conveys information about the complex characteristics of the nonlinear physical processes taking place as a consequence of the explosion to some extent. We present a thorough review of the characterization of arrows of time in time-series, and then provide specific details regarding their applications in passive acoustic monitoring. Visibility graph-based metrics, specifically the direct horizontal visibility graph of the instantaneous phase, have the best performance when assessing the arrow of time in real explosions compared to similar acoustic events of different kinds. The proposed technique has been validated in both simulations and real underwater explosions.
Highlights
Underwater explosions (UNDEX) are one of the loudest sounds that can be heard in the ocean and can disrupt everything from tiny plankton to blue whales [1,2]
We explore the arrow of time, a concept first introduced by Sir Arthur Eddington [16], to assess the feasibility of using arrow of time metrics in the characterization of UNDEX events
We have presented a rigorous study of the different techniques for assessing the arrow of time and their application to underwater acoustic events in general and to UNDEX events
Summary
Underwater explosions (UNDEX) are one of the loudest sounds that can be heard in the ocean and can disrupt everything from tiny plankton to blue whales [1,2]. Even though the use of UNDEX for fishing ( known as blast fishing) is illegal and has almost been eradicated, it is still seen in some areas in the world [6] This is a highly destructive method that destroys habitats (coral reefs in most cases), resulting in a drastic reduction in catches and affecting food security. Compact arrays of sensors provide a system that is easy to deploy, which in many situations gives sufficient localization accuracy Surveillance vehicles such as remotely operated vehicles (ROVs) [12] or gliders [13] can integrate UNDEX detection algorithms to perform mobile acoustic measurements in the immediate vicinity of a surveillance area. Possible situations may range from clipping in high intensity or very close-range UNDEX to low signal-to-noise ratios in the case of low intensity or detonations happening far away from the acoustic recorder
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