EMSO ERIC is proud to announce that the new groundbreaking project, “Submarine noise-Evaluation & Analytics using Low-cost Sustainable-sensing” (SEALS), has been successfully launched within the EMSO Physical Access Programme.

Led by Prof. Mohammad Belal, from the National Oceanography Centre (NOC), UK, with the collaboration of Scripps Institute of Oceanography, Woods Hole Oceanographic Institution, University of Southampton and University of Edinburgh, and hosted in Southern Italy, at the Regional Facility “Western Ionian Sea”, this project aims to tackle one of modern oceanography’s biggest challenges: efficiently managing and interpreting the enormous volumes of data (about 1 gigabyte per second!) generated by next-generation sensing technologies.

The SEALS project leverages the existing 28-kilometre subsea fibre optic cable, present at the EMSO’s Facility and deployed from shore down to approximately 2000m depth, to create a powerful, continuous observatory for open-sea processes by using Distributed Optical Fibre Sensing (DOFS) technology for the first time at this monitoring EMSO site.

 

How DOFS works: Turning a cable into a high-definition sensor

DOFS itself is the broad technology platform, not a single method, and its power lies in its different applications which are specialised to measure specific phenomena. The “journey” of this technology began in the early 1980s, with foundational paper demonstrating one of its first applications: Distributed Temperature Sensing (DTS), the capacity to measure temperature variations along the length of optic fiber, with a paper by A.H. Hartog from the University of Southampton, entitled “A distributed temperature sensor based on liquid-core optical fibres”, Journal of Lightwave Technology, 1(3), 498-509. This was a groundbreaking concept as it demonstrated for the first time that a standard optical fiber could itself act as a distributed sensor, rather than requiring discrete sensing elements attached to it. Over the following years, the same core DOFS principles were applied to create other methods, including Distributed Strain Sensing (DSS), for detecting stretching, compression, or bending in the cable, making it invaluable for monitoring the structural integrity of bridges, dams, and tunnels, and Distributed Acoustic Sensing (DAS), for measuring dynamic strain changes caused by acoustic energy (vibrations), that is central to the SEALS project.

At its core, the SEALS project operates by using light to sense the acoustic environment by turning the entire fibre optic cable placed at the EMSO’s Italian Facility into a virtual chain of thousands of high-fidelity hydrophones and seismometers to capture the signals from the underwater environment.

An onshore device called an “interrogator” sends thousands of light pulses down a standard fibre optical cable every second. These pulses serve as a baseline. When an external event happens around the cable, such as an earthquake, changing ocean currents, or mammals passing, it creates sound waves that physically disturb the cable and the properties of the light travelling within it are changed. This change is precisely measured in the backscattered optical signal. By analysing the timing and characteristics of this returning light, researchers can detect, classify, and pinpoint events with remarkable precision along the entire length of the cable, obtaining a detailed map of the diversity of disturbances in the underwater environment.

 

The Big Data challenge: The SEALS core objective

A key challenge is distinguishing between the multitude of signals captured. Each type of event creates a unique “vibrational field signature” in the data. 

For example, Belal explains: “Characteristics of vibrations (e.g., due to submarine geohazard, marine vessel motion and/or cetacean activity etc.) originating in different and/or same media, despite being at the same carrier frequency, can be different. These vibrational fields interact with the submarine cable and consequently influence the coherent optical radiation propagating within the optical fibre embedded in these cables. Use of a combination of optical and digital signals processing techniques on the propagating optical field allows for extraction and discrimination between events responsible for the origin of the interacting vibrational fields”.

The DOFS system, used in this project, captures every day 86 terabytes of data, a huge amount of information from the underwater environment, hosted in a local server of Belal’s team: “160 TB of data is generated in this initial test-phase of under 4-weeks. The data checks (any loss or corruption in data, e.g., due to power loss etc.) are underway which will be followed by some initial analytics to inform on signal to noise characteristics in space and over time. This will inform the use of bespoke algorithms to tease out information under poor signal to noise ratio scenarios”.

A central goal of the SEALS project is to validate the developed custom algorithms, designed to automatically scan and detect the big data coming from the seafloor in order to identify and classify events captured. 

 

The EMSO Western Ionian Sea Facility: A natural laboratory

Operated by INGV, INFN, and CNR-ISMAR, the Western Ionian Sea Facility is an ideal location for this research. This area, located at 25 kilometers off the coast of Catania, Sicily, is subject to seismic activity, due to tectonic activity for the collision of the African and European plates, and the vulcanic one, since it is dominated by the majestic presence of Mount Etna, one of Europe’s largest and most active volcanoes.

This dynamic environment provides a rich stream of data for testing and refining the system, the object of the SEALS project. Beyond monitoring seismic and volcanic activity, the project aims to detect:

  • Underwater landslides and sediment flows.
  • The presence and behaviour of marine life, particularly cetaceans.
  • Complex oceanographic phenomena, like internal waves and turbulence, crucial for understanding ocean mixing.

Data Processing and Validation

To validate the accuracy of the SEALS’s system, the data will be cross-referenced with measurements from the existing traditional co-located sensors at the EMSO’s Facility, such as those from INGV’s mooring (measuring oceanographic conditions) and seafloor sensors (like hydrophones, magnetometers, and seismometers) and INFN’s buoy (which it is planned to provide data on vessel activity on the surface). 

This synergy between innovative and traditional instrumentation is a hallmark of EMSO’s approach to integrated ocean observation.

“The collaborating partners are domain experts in physical oceanography, geoscience and marine seismology. Consequently, they contribute towards providing signal definitions of interest and their associated events kinematic & dynamics, which informs accurate and optimal use signals processing tools”, concludes Belal.

 

Prof. Belal would like to thank and acknowledge the support and contribution of the Western Ionian Sea group, led by Davide Embriaco, INGV,  for this work and is looking forward to working with them in future.

 

Author: Sara Pero, EMSO ERIC