Fibre-optic cables already lie on the seabed along almost every coastline – and they could soon start watching over people on land. A team from the University of Alcalá, working in the SAFE project, has shown that a single fibre can be turned into a network of thousands of sensors that pick up an approaching tsunami, at a fraction of the cost of buoys or seabed seismometers. It is a story about physics, the sea and doing the maths on costs – and at the end you can check whether you think like an early warning system designer.
Tsunamis are among the natural phenomena that researchers treat with the greatest respect. CORDIS describes them as one of the most destructive forces of nature, inflicting high human and material losses – and they are notoriously difficult to predict. What matters most is therefore not so much forecasting as quickly confirming that a wave really is on its way, and passing that information on to the authorities.
The tools for this already exist. The trouble is that they are expensive and do not always work as they should. Miguel González Herráez from the University of Alcalá puts it plainly: “Although there are some early warning technologies on the market like DART buoys and Ocean Bottom Seismometer (OBS) arrays, they come with high deployment and maintenance costs and have limited reliability.”
The SAFE project, funded by the European Innovation Council and coordinated by the University of Alcalá, set itself a goal that sounds almost like a riddle: to provide a low-cost, highly reliable tsunami early warning system without requiring any new infrastructure. The answer turned out to be lying, quite literally, under water.
“Our concept takes existing submarine fibre-optic cables and turns them into a 24/7 tsunami detector that works in real time,” explains Herráez.
At the heart of the solution is distributed acoustic sensing, or DAS. This technology uses light to generate distributed acoustic sensors along the entire length of a submarine cable. As a result, one fibre becomes an array of thousands of sensors spaced just a few metres apart. Importantly, the cable itself does not need to be modified in any way.
The approach has one more advantage: reach. “Since submarine fibre-optic cables are present along virtually every coast, this solution has the potential to massively enhance the available network of offshore sensors,” says the Alcalá researcher.
The project confirmed that its technology can detect changes in sea level – a strong predictor of tsunamis – with an accuracy of less than 20 cm. In practice, this means that the authorities can confirm a tsunami while it is still 50 km offshore.
The team does not intend to stop there. “We believe that if we continue to improve this technology, we will reach the 100 km mark – which equates to more time to prepare and more lives potentially saved,” says Herráez.
The second strong point of the SAFE system is money. Its capital and operating costs are at least ten times lower than those of ocean bottom seismometer arrays and DART buoys. The advantage comes from several elements:
Herráez sums it up like this: “If we add to this the fact that these other technologies are point sensors and that the SAFE system provides thousands of readings with a single piece of equipment, it is clear that our technology has many technical and economic advantages.”
The low price is not just a business argument here. The combination of higher reliability and lower costs is particularly attractive to developing coastal countries, many of which are the most vulnerable to tsunamis yet lack the resources needed to implement traditional early warning systems.
“Our solution is extremely versatile in that it can be used to considerably improve the tsunami warning capabilities of advanced countries or serve as a cost-effective alternative for those areas that cannot afford to deploy and maintain DART buoys or OBS arrays,” Herráez concludes. Project partners such as Aragon Photonics Labs are now working to develop the SAFE sensing solutions further and, eventually, to bring them to market.
SAFE is a good example of what modern security research looks like. It is not only about emergency services and procedures, but also about the physics of light, signal processing and knowledge of the sea. Students of engineering, the natural sciences and crisis management can see here that their fields are sometimes surprisingly close to one another.
It is also worth noticing the researchers’ approach. Instead of asking what else needs to be built, they asked how to use what already exists. That way of thinking comes in handy in a thesis, a team project and a first job.
A team from the University of Alcalá wants to turn submarine fibre-optic cables into a round-the-clock tsunami detector. DAS technology detects sea level changes with an accuracy of less than 20 cm and makes it possible to confirm a wave 50 km offshore, with 100 km as the next goal. The system’s capital and operating costs are at least ten times lower than those of buoys and seismometers, which gives a chance to countries that cannot afford costly coastal protection today.
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