INTEGRATING MONITORING TECHNOLOGIES TO SECURE SUBMARINE CABLES

BY JAN PETTER MORTEN, MARTIN CONNELLY, STEINAR BJØRNSTAD, JAN KRISTOFFER BRENNE, AND ANDREW DESFORGES

The crippling effects on society and business from fiber breaks are a worry for cable owners and governments. The most common cause for such cable damages are bottom-trawl fishing and ship anchors that snag cables on the seabed. For regions with limited route diversity, this can result in major disruption like the multiple incidents that damaged the cables connecting Shetland and Faroe to the mainland in October 2022. The threat to submarine telecom systems has been exacerbated by the recent deterioration of global security, making willful sabotage to disturb marine infrastructure a scenario that must be considered.

Fortunately, substantial resources are made available for repairing submarine cables in case of an incident. The coordinated coverage of dedicated repair ships around the world ensures quick response. The spending on the maintenance agreements governing these capacities show that cable damage is considered a serious condition justifying continuing investments to mitigate.

A submarine cable system comprises sophisticated terminal equipment for monitoring the performance and integrity of technical components like modems and repeaters. This supports the reliable and stable telecom connections that we rely on. However, very limited attention is directed to protecting the cable along the seabed route. Other than cable burial at installation, direct monitoring for potential threats is often limited to sporadic inspection surveys to determine the state of the cable.

The lack of comprehensive seabed cable monitoring is perhaps to be expected, since it is expensive and inefficient to do subsea inspections over long distances along cables. Persistent cable threat monitoring is therefore usually limited to surface monitoring using e.g., guard vessels, collection and monitoring of AIS (automatic identification system) vessel movements data, and some places radar. Until recently, cost effective and robust seabed sensor tech- nologies were not available for the distance scales required. However, this situation is no longer the case as fiber optic sensing technologies have now enabled real-time and longrange monitoring suitable to protect marine assets.

Fiber Optic Sensing For Threat Monitoring

DAS (distributed acoustic sensing) utilizes properties of backscattered light in fiber optic cables to determine any vibrations and waves influencing the cable. Such disturbances can be due to e.g., nearby objects moving on the seabed, or physical contacts with a cable segment exposed in the water. This makes the DAS measurement very well suited to detect fishing gear and anchors on the seabed, as well as any equipment that snags or attaches to the cable. The DAS data have a dense spatial resolution and can locate a disturbance close to the cable on the meter scale, and will sample the interaction at frequencies typically above 500 Hz. Due to the high sensitivity and low-noise environment in the ocean, it is even possible to locate and track the source of a seabed interference that is offset by up to 3 km from the cable, and at a range of 120 km along (Waagaard et al., 2022).

The DAS monitoring only requires connection to one end of an optic fiber at the cable landing. Moreover, the operation of DAS monitoring can coexist with data traffic in the same fiber (Brenne et al., Suboptic 2023), making the technology cost effective both to deploy and operate. The data processing is implemented as edge computing that handles the massive data rate from the instrument to generate sparse information about location and characteristics for detected objects in real time. This output is suitable for distribution to an online and live mapping service, or database storage for long-term statistics about activity along a cable. Figure 1 provides a schematic overview of the operation of the system.

INTEGRATED DAS AND AIS REAL-TIME TRACKING

Analysis of AIS data is used by cable operators to safeguard marine assets and is realized as a real-time service giving monitoring teams a live view of vessel activity near submarine cables. The system will automatically generate alerts whenever, for example, a fishing vessel is reporting to operate within a protection zone. The surface data from AIS can be integrated with the sub-surface detections from DAS to enhance the situation understanding. The identity and reported status of the fishing vessel can be corroborated with tracking data for any fishing gear on the seabed. Since the two data types are independent, the DAS tracking data can be used to complement the coverage if the AIS records are not available due to e.g., poor coverage of land-based antennas. This is very relevant as experience has shown that in some areas, 2/3 of the fishing activity goes undetected from AIS receiver stations.

A long-term deployment of an integrated DAS and AIS cable threat monitoring system on a North Sea telecom cable has detected a large number of fishing and anchoring events (Morten et al., Suboptic 2023). We have analyzed the performance of this system for real-time applications as well as for determining seasonal and geographic traffic hotspots. In Figure 2 we show a snapshot from the cable monitoring GUI. The captured event is characteristic of bottom-trawl fishing activity that represents a risk to damage the cable. The seabed cable route is shown in the map as a red line, with the tracks from about one hour of movements from the positions detected for the vessel by AIS (yellow line, triangle symbol) and for the seabed trawl moving on the seafloor by DAS (blue lines, circle symbol). The green zones designate 500 m, 2 km, 4 km distance from the cable. The data show that the fishing vessel approaches the cable from north-west and performs a turn within the cable protection zone, with the seabed gear crossing the cable twice. The direct observations of the seabed activity combined with the vessel data enables a well-informed situation understanding that could trigger a decision to make a vessel intervention. A monitoring team could make the vessel crew aware of the risk to damage the cable and loss of the fishing equipment. If necessary, accurate information about the incident can also be provided to guard vessels or coastguard for appropriate action.

Impact On Cable Security And Cost Of Cable Ownership

The cost of an offshore cable repair operation can be on the million-dollar scale. Because of this high cost, the savings from even a single negated repair due to the operation of a DAS and AIS cable threat monitoring system will make it cost-effective. The investment in hardware and operations to support the integrated DAS and AIS system are modest in comparison to repair vessel operations.

Much like the effect on road safety from automated speed control, the adoption of active cable threat monitoring would also result in increased awareness of about the risks of operating in the proximity of marine assets. This will reduce the number of outages and the cost of cable ownership. Further cost reduction will be achieved from the statistics of where and when potentially hazardous subsurface activity typically occurs. This will enable targeted cable protection measures like e.g., ensuring proper cable burial in elevated risk segments over time, placement of rock bags, and dialogue with mariners.

For the future, we anticipate that cable surveillance enabled by DAS will transform the way cable risk and operations are managed. Long-range and real-time monitoring that identifies seabed activity will also be an effective response to increased cybersecurity and sabotage threats. These fiber optic solutions can also be integrated in other submarine installations such as power cables, offshore wind farms, and pipelines. The data coverage from such sensor systems will also enable other applications to benefit wider society for example coastal surveillance, seismological hazards early warnings, marine biology studies, and climate change research.

• O.H. Waagaard, J.P. Morten, E. Rønnekleiv, S. Bjørnstad, Experience from long-term monitoring of subsea cables using distributed acoustic sensing, OFS conference, U.S., 2022.

• J.K. Brenne, J.P. Morten, J. Jacobsen, O. Ait-Sab, A. Calsat, P. Plantady, J.-F. Baget, Distributed acoustic sensing solution for repeatered networks, SubOptic conference, Thailand, 2023.

• J.P. Morten, M. Connelly, S. Bjørnstad, J.K. Brenne, A. Desforges, Integrated DAS and AIS for real-time cable threat monitoring, SubOptic conference, Thailand, 2023. STF

JAN PETTER MORTEN is Principal Engineer at ASN Norway, focusing on fiber optic sensing applications and signal processing. He received a PhD in theoretical physics in 2008 from NTNU, Norway and has experience in geophysical imaging, electromagnetics, ultrasound, and development of HPC software.

ANDREW DESFORGES Co-Founder & Director of Operations of UltramapGlobal. Andrew Desforges (“Des”) created UltramapGlobal in 2013 with fellow Director Martin Connelly. Des has led geo-information systems, application development and data capture projects since 1998. He’s seen demands on ocean-based cable protection intensify exponentially as the cable population, and associated threats, also increase.

JAN KRISTOFFER BRENNE is R&D Manager at ASN Norway, with over 20 years’ experience in fiber optics sensing technology and was heavily involved in the development of the distributed acoustic sensing system OptoDAS. He received a MSc in physics in 2002 from NTNU, Norway and has experience in low-noise lasers, fibre Bragg gratings, interferometric sensing, and distributed fiber optic sensing.

MARTIN CONNELLY is Co-Founder & Commercial Director of UltramapGlobal. Martin with co-director Andrew Desforges created UltramapGlobal in 2013, to focus on reducing subsea cable strikes – to zero. UltramapGlobal has achieved this in so many of our territories, it’s a goal we are comfortable in retaining.

STEINAR BJORNSTAD is strategic competence and research manager at Tampnet AS and has previously worked in several industry companies including Telenor and Ericsson and founded TransPacket. He is also since 2004 Associate professor IIK/NTNU Trondheim, Norway and from 2018 Senior research scientist SIMULA Oslo MET, Norway. He holds a master in physics from the University of Oslo (1991) and Ph.D. in telecommunication from the University in Trondheim, Norway (2004). He founded TransPacket in 2009 and has been involved in IEEE standardization, 802.1 Ethernet and 1914.1/1914.3 mobile fronthaul. He is author/co-author of more than 60 scientific papers and has several international patent-families.