Ocean Space Surveillance and Real-Time Event Characterization Using Distributed Acoustic Sensing on Submarine Networks
Alan F. Baird, Jan Petter Morten, Volker Øye, Steinar Bjørnstad
Abstract
Abstract Distributed acoustic sensing (DAS) can be deployed on existing submarine fiber-optic cables to add long-range sensor capability to the cable infrastructure. In this article, we present the following: (1) observations and analysis of impulsive source events from long-term DAS measurements on a North Sea submarine telecommunications cable. The observations include local earthquakes originating in the crust below the cable, underwater explosions originating in the water column, an onshore explosion from the nearby coast, and examples of sonic booms from supersonic aircraft and a suspected meteor from the atmosphere. The analysis reveals how the signals from earthquakes and underwater/aerial explosions can be distinguished in the data domain based on their frequency and apparent velocity characteristics. (2) A processing workflow enabling real-time marine surveillance including detection and location of explosions in the water column. The processing is verified by corroborating local earthquakes and underwater explosions with independent data sources. We show that different types of waves can be identified including seismic body waves, hydroacoustic waves, and atmospheric infrasound waves coupled through the water column. Tracking the travel-time moveout along the nonstraight cable route allows for positioning of the source, which we demonstrate by migration stacking of the recorded signal. Signal processing suitable for real-time classification and source location is applied to the recorded data and shows how ocean space surveillance at scale can be realized.