TNO develops optical detector to protect cables on seabed

11 Jun 2024

Netherlands Geological Survey (part of TNO) has conducted successful tests in the North Sea.

Netherlands-based research center TNO has developed a method to automatically detect maritime traffic in the vicinity of subsea infrastructure. Using redundant optical fibers in fiber-optic cables, (“dark fibers”), 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.

Offshore cable and pipeline infrastructure continues to grow, to meet demand for energy and communications. Although most countries are dependent on this infrastructure, recent events since the Russian invasion of Ukraine, have shown just how vulnerable it is.

Damage to cables and pipelines can pose a serious threat to lives and livelihoods and currently there are no adequate systems in place that allow this infrastructure to be properly monitored and secured, contends TNO: “Underwater, we are deaf and blind, so to speak,” says the latest statement from the research group.

Power and telecoms cable tests

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 to detect maritime traffic in the vicinity of these cables. Using a wind-farm power cable and a telecommunication cable that runs to the United Kingdom (more than 100 km long) as sensors, vibration data were obtained and maritime traffic close to these cables was detected and located.

“Using dark fibers, we were able to detect and track ship movement close to cables on the seabed. This technique can thereby make an important contribution to safety in the North Sea,” commented Vincent Vandeweijer, a geologist and geophysicist at the Geological Survey of the Netherlands.

A device, called 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 and located. Data from the automatic identification 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. In the latter case in particular, an early warning can be automatically triggered to inform the relevant authorities of suspicious traffic.

How it works

Traditionally, geophysicists at the Geological Survey of the Netherlands focus on acquiring and processing data to characterize the subsurface and monitor subsurface processes and seismicity. Vincent Vandeweijer, geologist and geophysicist at the Geological Survey of the Netherlands, said, “In our field, we use dark fibers to detect and locate earthquakes, among other things.

“We wondered, following the Russian 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 fibers, we were able to detect and track ship movement close to cables on the seabed. This technique can thereby make an important contribution to safety in the North Sea.”

The video below illustrates the new method developed by geologists and geophysicists: