Preliminary assessment of ship detection and trajectory evaluation using distributed acoustic sensing on an optical fiber telecom cable

Abstract

We detect maritime vessels on a 41.5 km long fiber optic telecom cable using distributed acoustic sensing. We measure noise emitted by the same tanker cruising one day at a distance of 5.7 km from the shore, above 85m of water, and the following day at a distance of 20 km from the shore, above 2000 m of water. The acoustic emissions of the tanker result in measurable strain rate on the optical fiber cable laid on the seafloor and probably, for some sections, covered by sediments. The spectral signature of the engines of the ships, the doppler effect, and the apparent velocity of the acoustic waves on the fiber allow to separate the ship noise from the environmental and the DAS interrogator noises. The broad band sensitivity of the distributed acoustic sensing allows to identify tanker acoustic noise at frequencies ranging from 16 to 100 Hz on the noise content measured up to 1kHz. At 85m water depth, the signal to noise ratio is high, and the trajectory of the boat is recovered from beam forming analysis of the distributed strain rate measured every 6.4m. At this shallow depth it is possible to track the position of the tanker up to 2 km away from the cable. The main features of the intensity of the acoustic noise in space and time is well model using a ray-based model of the acoustic wave propagation in the sea and converted into longitudinal strain rate, as it is seen by the cable. On the open sea, at 2000m water depth, the acoustic signal of the ship is more attenuated, however narrow bands signals below 50Hz are still detected by the DAS. In both route of the cruising tanker, we assess the possibly to use the Doppler shift of the emitted frequency to estimate the tanker velocity. These results confirm the high potential of DAS technology using telecom cable for a remote and quantitative monitoring of the maritime traffic and for vessel tracking on shallow water but also at great depth.

Noise Levels and Signals Observed on Submarine Fibers in the Canary Islands Using DAS

“…Rønnekleiv et al (2019) showed that DAS is capable of recording acoustic waves from ships, too. Rivet et al (2021) further explored the potential of this technology to detect and track ships. They concluded that the strain changes in the cable can be caused directly by pressure waves traveling through the water layer or through the sediments for slightly buried sections of the cable.…”

Eavesdropping at the Speed of Light: Distributed Acoustic Sensing of Baleen Whales in the Arctic

“…However, the decisive characteristics to classify baleen whales is the spectral content of the signal (McDonald et al, 2006;S ̌irovićet al, 2017). We therefore propose a spatio-spectral representation of the DAS recordings or f-x plot, as employed in (Rivet et al, 2021), to show the spectral signature and its evolution against the distance. The method is detailed in § 4.…”

“…Using an interrogator, DAS technology re-purposes existing dark fiber optic (FO) cables to record nano strain (Culshaw and Kersey, 2008) and has the potential for realtime monitoring over tens of kilometers (up to 171 km (Waagaard et al, 2021)) with a spatial resolution of a few meters (Goertz and Wuestefeld, 2018;Waagaard et al, 2021). Initially applied to geophysical data collection (Schenato, 2017;Hartog et al, 2018), DAS has recently aroused interest with waterborne sound sources, e.g, it has been used for near-surface ship detection and bearing estimation in the Mediterranean sea (Rivet et al, 2021). Quality assessment of the data was performed using controlled airguns sources compared (a) to ocean bottom seismometers recordings in Japan (Matsumoto et al, 2021) and (b) to seismic streamers in Norway (Taweesintananon et al, 2021).…”

PubDAS: a PUBlic Distributed Acoustic Sensing datasets repository for geosciences

“…DAS recordings were also used for ambient noise interferometry (e.g., Zeng et al, 2017; E. R. , offering the possibility to retrieve repeatable signals (i.e., Rayleigh and Love waves) for near-surface characterization (E. Dou et al, 2017) and aquifer monitoring (Rodríguez Tribaldos & Ajo-Franklin, 2021). In addition, subsea telecommunication fibers have been used to monitor ocean dynamics (Lindsey et al, 2019;Sladen et al, 2019;Williams et al, 2019Williams et al, , 2022 but also to detect earthquakes (Lior et al, 2021; and acoustic phases (Rivet et al, 2021;Ugalde et al, 2022;, image the near-shore subsurface (Z. J. Spica, Nishida, et al, 2020;Z.…”