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TNO, an independent and pioneering applied science and technology organisation, has developed a method to automatically detect maritime traffic in the vicinity of subsea infrastructure. Using redundant optical fibres in fibre-optic cables, also known as dark fibres, as sensors makes it possible to pick up vibrations from maritime traffic. TNO has successfully tested a method, which allows a large area along the path of cables and pipelines, to be monitored in order to prevent intentional or unintentional damage.

Vulnerable infrastructure

The offshore cable and pipeline infrastructure is steadily growing, to meet the demand for energy and communication. Although the people are very dependent on this infrastructure, recent events have shown just how vulnerable it is. Damage to cables and pipelines can pose a serious threat to daily lives and currently there are no adequate systems in place that allow this infrastructure to be properly monitored and secured.

Successfully tested using wind-farm power cable and telecommunication cable

Specialists with geophysical expertise (including earthquake detection) from the Geological Survey of the Netherlands (part of TNO) have conducted successful tests in the North Sea. Using a wind-farm power cable and a telecommunication cable that runs to the United Kingdom (more than 100 km long) as sensors, data was obtained and maritime traffic close to these cables was detected.

Use of laser light

A device, (a DAS interrogator) connected to the end of the cables (on land) uses laser light to detect vibrations along the entire cable length, over very long distances. These vibrations can be caused by earthquakes, environmental noise, ocean waves or even the sounds of marine mammals, but also by maritime traffic.

By processing the data using an algorithm, it is possible for maritime traffic to be detected. Data from the automatic identification (opens in a new window or tab) (refers to a different website) system (AIS) were used to verify the results. In the event of a mismatch between these data, the vibrations could be caused by a source outside the range of the AIS or a source that has its AIS turned off (intentionally or unintentionally). In the latter case in particular, an early warning can be automatically triggered to inform the relevant authorities of suspicious traffic.

Method developed by geologists and geophysicists

Traditionally, geophysicists at the Geological Survey of the Netherlands focus on acquiring and processing data to characterise the subsurface and monitor subsurface processes and seismicity. Vincent Vandeweijer, geologist and geophysicist at the Geological Survey of the Netherlands: “In our field, we use these ‘dark fibres’ to detect and locate earthquakes, among other things. We wondered, following the attack on the Nordstream pipelines, whether our approach could also be used to detect ships located close to infrastructure situated on or just below the seabed. Our tests showed that this is indeed the case. Using dark fibres, we were able to detect shipping close to cables on the seabed. This technique can thereby make an important contribution to safety in the North Sea.”