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Advanced applications of fiber optic sensing in subsea environments

Feb 7, 2024 9:18:19 AM / by George Brandenburg

Our previous article about cable sensing delved into the fascinating world of fiber optic transmission and sensing technologies, uncovering how these innovations reshape data communication and monitoring. In this continuation, we venture further into the specialized realm of distributed fiber optic sensing, exploring its groundbreaking applications in various sectors.

Starting with the possible applications

From defense and energy to environmental research, this technology is not just about data transmission; it's about gaining unprecedented insights into the subsea world. Join us as we explore how distributed fiber optic sensing is becoming a game-changer in understanding and monitoring the complex dynamics of our oceans.

Some of the possible applications are:

  • DoB, Depth of Burial analysis for trenched cables
  • RTTR, Real Time Thermal Rating for hotspots, also known as DCR
  • DTSS, Distributed Temperature and Strain Sensing
  • General electrical load and condition monitoring

Distributed Fiber Optic Sensing in Defense and Research

Quite a lot of research is being done to increase the amount and effectiveness of subsea fiber optic sensing for these applications. To date, the industries that have invested most in this type of sensing are defense, research, and energy, including oil & gas and renewables.

DeRegt has worked with the Dutch Ministry of Defense to develop a subsea data transmission cable with fiber optic sensing capability to ensure secure communications. Using the principle of distributed acoustic sensing (DAS), some fibers in the cable are linked to a laser light source and an interrogator. 

If an adversary were to pry open the cable or to place a device next to it to eavesdrop on transmissions, a disturbance in cable vibrations can be detected, located, and analyzed by changes in the light frequency in the fiber. Distributed fiber optic sensing cables also have great potential for research, as these can detect earthquakes, tsunamis, and even the presence of marine life and ships using DAS sensors.

Distributed sensing for energy applications

For ocean renewables such as tidal turbines, a depth of burial (DoB) analysis uses a fiber in a static cable to analyze what happens to a signal that goes through a cable that is secured to the seabed. A fiber sensor integrated into the power cable can detect in real time whether and where that cable has been unburied or otherwise moved. If the cable is flopping around it needs to be secured in place before it breaks.

Offshore wind parks can now use fiber optic sensors integrated into their buried power cables to provide real time continuous monitoring of the DoB. Software by Marlinks can detect and analyze data from an interrogator hooked up to fibers in the cable. Using changes in temperature and strain (DTSS) the software can determine whether and where the cable has become unburied, due to constant movement of sand on the seafloor.

Distributed sensing can also be used to detect electrical load and perform condition monitoring of the cable for fatigue, for instance. For an offshore oil platform, a single fiber could be added to a cable running from the platform to a well to measure distributed temperature and strain sensing (DTSS) for possible leak detection or disruptions to operations. 

A business case for fiber optic sensing

With the recent burst of technology advancements in fiber optic sensing, business cases can be made for quite a few applications. On the seabed or buried under the sea floor, operators have no way of knowing what is happening to equipment – until it malfunctions. Fiber optic sensing technology provides a picture of what's happening on or under the seabed to keep an eye on the status of hundreds of millions of dollars’ worth of equipment.

The case for ensuring secure communications using fiber optic sensing with data cables on the seabed is critical both for national defense and for internet companies, such as Google and Facebook. There is no real alternative to monitoring these deep-sea cables for disruptions or wiretapping with distributed sensing technologies, for protecting both equipment and data.

Utilizing Fiber Optic Sensing for Subsea Cable Protection

For preventive maintenance applications where a subsea cable is fixed to the sea floor, a cable that becomes unburied is unprotected. Distributed fiber optic strain sensing can measure whether the static cable is being moved too much by wave action, allowing you to mitigate the problem before cable failure, with its high replacement cost. 

To prevent hotspots where it might get too warm and melt part of the cable, a single mode fiber with Bragg gratings to measure the temperature of 100 or 150 different points on the cable, is easier and far less expensive than adding 150 sensors and interconnecting them. 

Fiber Optic Sensing: A growth industry

At DeRegt, we are seeing big step changes in the fiber optic sensing industry as defense and other communications networks look secure communications for their submarine cables, to protect them from data theft and disruption by threat actors. 

Although fiber optic sensing has been used for some time, many of these technologies, especially distributed temperature and strain sensing (DTSS) are quite new and we see quite a lot of advancements. The technology requires highly accurate interrogators, and the development of these interrogators is rapidly growing. 

With the ongoing energy transition, fast-growing ocean renewables such as tidal turbines will require a large increase in cable installations on the seabed. This should prove to be a catalyst for growth in the use of fiber optic sensor technology, which ultimately should lower the cost of expensive interrogators and software.

Get experienced help with fiber optic sensing cables

To implement fiber optic sensing in a submarine cable requires knowledge of both cable design and manufacturing, as well as access to interrogators and software to analyze the sensor data. 

At DeRegt, we have years of experience with the cable layout process, including integrating fiber optics into the cable and extruding the protective plastic layers surrounding it. We know how to design the cable, including the optimal placements for the fibers inside the cable. And we know what influences attenuation of the signal and what doesn't. We're aware of these complex factors and we can advise clients who would like to take specific measurements on the type of fiber sensor technology to use.   

DeRegt has designed and built subsea cables containing large numbers of optical fibers. One cable, for instance, includes a total of 492 single mode fibers, but the cable itself remains compact, due to the small diameter of each fiber.  At the same time, it can transmit a tremendous amount of data. 

Contact George Brandenburg to discuss your fiber optic sensing project.


Topics: Renewable Energy, Subsea cables

George Brandenburg
Written by

As Business Development Manager at DeRegt, I specialise in co-creating high-performance subsea cables for the renewables industry. Together with pioneers in solar, wave- and tidal projects, we develop dynamic cables that are cost-effective and are built to last the harsh conditions at sea. Do you have questions about connecting the grid? Let's tackle your challenges together.

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