How Distributed Fiber Sensing Is Advancing Subsea Cable Monitoring

As published in the September Issue of SubTel Forum Magazine

By Mark Englund
September 22, 2022

 When the first telegraph message sent via subsea cable was transmitted in 1868 between the UK and Canada, a lack of cable capacity and repeaters restricted the cable transmission to 2 words per minute. Although piecemeal, messages arrived quicker than the next fastest transmission method: steamships, which would require 10 days to travel between the two locations.[1] Within two years, the transmission speed had already improved to 20 words per minute. Fast-forward 150 years later and subsea cables have evolved to become communication superhighways, responsible for transporting 99% of internet and cloud traffic globally across approximately 500 submarine cables that span 1.3 million kilometers of ocean floor.[2]


Subsea power cables, too, are looked to as a game changer in the energy sector as the solution to transmitting high-voltage electricity underwater. Use cases for subsea cables continue to develop. They play a central role in harnessing offshore energy, with impressive projects like the recently completed North Sea Link[3] drawing attention to countries’ need to reap the benefits of superior ocean wind activity and tidal power generation. Given the increasing dependence the global economy has on both connectivity (internet and cloud) and power transmission, subsea cables are therefore increasingly vital, which is why it is crucial that innovations in threat mitigation keep evolving to ensure reliable delivery of critical connectivity and power to our communities.


Much like the evolution of subsea cables themselves, distributed fiber optic sensing, and specifically vibration detection and ranging (VID+R) technologies, have seen rapid growth and are reaching an inflection point in adoption. Fiber sensing benefits cable operators by providing instantaneous awareness of threats across every meter of the long linear asset for the first time. This type of actionable real-time information drives clear cost savings and avoids downtime. While fiber optic sensing is increasingly being adopted for telecommunications cables, it remains a lesser-known solution for power cables. With the distributed fiber sensing (DFS) market expected to grow at a compound annual growth rate of 7.3% over the next eight years, reaching a total market value of $2,553.5 million USD by 2030[4], subsea power operators have plenty to gain by paying attention to this technology in the coming years.


The Evolution of Distributed Fiber Sensing for Subsea Power Cable Monitoring

Undoubtedly, the vast majority of subsea cable outages each year are caused by external aggression, including anchor drag and bottom trawling events from fishing vessels. Impacts from natural disasters like tsunamis are another leading cause of disruption, along with geological shifts. Sometimes the damage is massive and apparent, like the 2008 submarine cable disruption in the Mediterranean Sea that left millions without internet[5], or the subsea power cable cut in 2020 that left 18,000 homes on the Isle of Skye without power, forcing the provider to call on a diesel-fueled power station to provide back-up electricity[6]. Other times, near misses or partial strikes can damage cables without immediately cutting power. Such latent damage can go unnoticed for a period before inevitable cable failure occurs, requiring repairs even years after the damaging event. In any scenario, cable breaks and faults interrupt vital supply. Repair costs can be up to 10 million pounds, or $12 million USD, and are usually accompanied by reputational damage and lost revenue on top of the direct repair costs. Typically, a jointing vessel will need to be mobilized and the jointing operation can often take from 40 to 60 days to complete the repair[7], adding to the costs.


As subsea cable operators are aware, they are one of the few pieces of critical infrastructure that are essentially invisible once deployed to the bottom of the ocean – in contrast to almost all other critical infrastructure, the subsea cable owners have virtually no idea what is happening around their assets. There have been protection techniques that monitor what is happening directly above their cables. Traditional methods include AIS beacon monitoring, surface ship patrols and aerial survey; however, these methods are easy to avoid (AIS beacons turned off), have large time/space gaps in the surveillance of the asset, are costly and their operational times are limited and impacted by weather. Fundamentally, these surveillance approaches are not directly on the asset and are not the full length of the asset 24/7/365. Enter distributed fiber sensing technology.


As previously mentioned, fiber optic sensing is increasingly being adopted for telecommunications cables, but is a lesser-known solution for subsea power cables. However, many power cables are constructed with fiber optics built in to serve double duty as telecommunications cables as well as electricity transporters. This allows for subsea cable monitoring via DFS, and more specifically the game-changing category of, VID+R. VID+R sits alongside distributed temperature and strain sensing in the DFS portfolio but is unique in one very powerful aspect – the very high sensitivity of VID+R is cable of detecting and classifying objects and events that are on but also off board the cable. This is also achieved over a long and continuous length via sensing and analyzing the unique vibration signatures of a given object and/or event. In this context, VID+R brings a total and sustained wide area surveillance capability around the marine cable for unprecedented situational awareness for the cable owners. This surveillance capability is easily deployed over the fiber optic strands already embedded in subsea power cables to measure changes in temperature and structural integrity.


Because of their wide reach, fiber optic infrastructure can be leveraged as a massive, dense, long-term gapless sensing array. Utilizing advances in photonics, hybrid cloud computing, machine learning, and artificial intelligence, DFS inside subsea cables is essentially leveraging standard telecommunication optical fiber for a new use case. With DFS, new Sensing-as-a-Service digital awareness products are providing 24/7/365 cable observation that detects a wide range of occurrences around the cables, including:

  • Live cable strike monitoring
  • Burial condition awareness
  • Geotechnical surveying below fiber
  • Vessel detection and tracking

For subsea power companies, there are significant advantages to be gained with the application of this proven technology. Subsea telecommunications cables are equally as vulnerable and under-protected as subsea power cables. Historically both classes of infrastructure have lacked real-time alerts that defend against events that lead to cable breaks and result in significant revenue loss.


The Case for DFS for Subsea Power Cable Monitoring

Distributed Fiber Sensing advancements are changing the way we monitor subsea cables, and in particular, sensing as a service represents the future of DFS for real-time detection and classification of external aggressors, precise damage locating, and the ability to aid in assigning culpability. Because of their wide reach through existing fiber optic cables, VID+R technology is superior for subsea cable monitoring in several key ways:


Total situational awareness for the first time

This “always on” and total length surveillance form of protection on the cable enables continuous threat monitoring with real-time reports served up 24/7 on the asset and the option to contact or interdict the threat before damage occurs.


Diagnosis, recovery time and cost

Consequential loss claims resulting from power cable damage can be substantial and subsea power cables cost approximately $1,200 per meter, or $1.2 million per kilometer, making monitoring an important form of insurance. Accuracy and precision in fault localization cut down on time to locate issues along hundreds of kilometers of subsea cables, thereby speeding up the repair and reducing costs over time. Eliminating unplanned power interruptions also increases revenue and decreases supply penalties.?



By helping to eliminate cable strikes and reducing the amount of unplanned reactive emergency repair works, DFS monitoring can reduce onsite risks of accidents from repair crews, as well as danger to any third parties near the site of cable damage or potential tsunami or subsea volcanoes.



 Today, most of the damage to submarine cables occurs in shore-end, shallow water and most of that damage is due to anchor drag and fishing net trawling. High-risk areas are also found at cable protection zones and near landing stations where there is an increased risk of multiple cables being taken out by the same event.


Integration with AIS can aid and assist in assigning culpability of any damages incurred. If a ship is the cause of such damage, and the cable operator can prove the negligence of that ship, then the operator may well succeed in recovering substantial sums in damages from the ship owner. A strong deterrence effect also arises as vessels operating in and around protected cables now know that their activities are traceable, leading to incentives for skippers to act in a less risky manner.


By 2028, the subsea power cable market size is expected to reach upwards of $11.82 billion USD[8], an increase of more than $4 billion USD from its 2021 value due to increasing investment in offshore energy and rises in cross country subsea power connections and underwater data centers. With greater lengths of costly subsea infrastructure to protect, the power industry is primed to join the subsea telecoms community in greater adoption of time- and money-saving tech like DFS services and move closer to the goal of preventing damage from occurring in the first place.


By eliminating the risk of interruption and boosting the security of supply, subsea cable operators can play an important role in meeting growing stakeholder expectations and regulatory demands while securing the future of subsea cable protection for future decades through DFS and VID+R technology.


About the Author

Mark Englund is Founder and CEO of FiberSense. Mark has over 25 years’ experience in sonar, optical fiber technology, engineering and business building.

He has a track record for seeing new market opportunities early and a pragmatic approach to building and positioning businesses to effectively engage these opportunities. This track record has been built over 25 years as an engineer, entrepreneur and business owner around a singular focus on the question of where the key value drivers are sitting in optical fibre networks and sensor systems.

These insights have come from a diverse experience base as 1) Head of the Optical Fiber Sensor laboratory, DSTO Australia 2) Founder, executive director and CEO of an optical fiber component company supplying high performance fibre Bragg gratings for sensing and telecommunications, 3) a US business development executive of a $1B subsea telecommunication cable supplier in to carriers and the supertechs and 4) a US business development & strategy executive of a $4B business spanning the total optical fiber network relevant to Cloud (subsea & international, terrestrial and in data centre).

Mark has an honours degree in Engineering from the CDU and a PhD in optical fiber sensing from the University of Sydney and is a member of the Australian Institute of Company Directors.

Mark is a keen promoter of new business models.







[6] In fact there was a need to airlift extra diesel generators from the mainland for redundancy




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