We cannot manage what we cannot measure – Is DAS a game-changer in ocean soundscape mapping?

Traditional acoustic sensing methods in the ocean are generally expensive and sparse. We are now embarking on a new era, beyond the ´century of undersampling´, enabled by marine robotics and other technical advances. One of these is Distributed Acoustic Sensing (DAS). DAS is an exciting idea that has been around for a couple of decades but has only recently reached sufficient signal-to-noise to be considered a practical sensing system. DAS is able to turn a Fibre-Optic (FO) cable into a string of virtual hydrophones using a photo-electronic `interrogator´. The interrogator is able to sense along more than 100km of FO cable with (typically) 4m resolution, resulting in an unprecedented long array of some 25,000 or more virtual hydrophones. Recent results from data acquired from two FO cables off Svalbard in the high north have shown that we can detect, locate and track multiple whales (including swim speed and direction) along a corridor around a cable over 60km long by 19km across. An example 5 hours of data tracked some 8 fin whales simultaneously. We believe that DAS is an exciting new tool for remote real-time acoustic sensing in the ocean that could be developed and integrated with other observational systems to empower responsible management and risk mitigation through near real-time information from extended regions.