Assessment of Arrow-of-Time Metrics for the Characterization of Underwater Explosions

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.

Acoustical Behavior of Delphinid Whistles in the Presence of an Underwater Explosion Event in the Mediterranean Coastal Waters of Spain

“…This is mainly due to the amount of energy released into the aquatic medium in a very short period of time. The SPL may exceed 250 dB re 1 µPa at 1 m [1,2], creating shock waves followed by a subsequent loading effect (known as the bulk effect) [3,4]. Marine fauna can be affected in different ways and severity depending on the distance from the source and the amount of energy released in the explosion.…”