With security increasligly critical to safe and efficient rail operations, PETER DERRY considers the benefits of distributed acoustic sensing (DAS), the ease with which it could be implemented and the potential risks

The detection of sound isn’t a property you would immediately associate with fibre optic cables. Yet the same cables that are transmitting our emails and telephone calls around the world can also be used as an early warning system that listens for potential threats or disruptions.

It sounds futuristic, but the concept behind distributed acoustic sensing is actually quite simple. Optical fibres carry pulses of light from one end to the other. If a disturbance occurs – say, for example, an object landing near the fibre optic cable – the vibrations will cause disruptions within those pulses of light which, with the right monitoring device in place, can be analysed to determine the strength, nature and location of the disturbance.

The technique can be extremely accurate. Configured correctly, it can pick up something as insignificant as a footprint, and with the proper monitoring can even differentiate between a human and an animal – a prospect of great significance when it comes to security. Distributed acoustic sensing (DAS) could also be used to monitor for potential defects in vehicles and machinery; picking up tiny changes in engine noise levels that could signify a defect or imminent failure.

The technology is already being used to protect assets worldwide, most notably in the oil and gas industry where operators deploy DAS to protect long, deserted and difficult to police stretches of pipeline. The similarities with the rail sector, where operators are responsible for thousands of kilometres of track and vast amounts of rolling stock, are clear. So could this nascent technology be the next big thing for the industry?

Bright prospects
Distributed acoustic sensing certainly has a great deal of potential as a rail solution, not least because a large portion of the infrastructure it requires is already in place.

Fibre optic cables are often laid alongside railway tracks, in depots and close to other assets. Transforming this existing infrastructure into a usable DAS system would simply involve setting up monitoring devices in optimum places along the line, and making sure they are configured correctly to capture any disturbances.

As for areas where the required infrastructure is not yet in place, laying dedicated cables could still prove a more cost-effective means of protecting rail assets than other, more expensive systems currently in use – most notably in terms of the distances that DAS systems can monitor effectively. The investment required to install DAS would be significant, but still viable relative to the value of the assets requiring protection.

Thanks to advances in digital technologies, DAS would complement rather than replace other monitoring techniques. We can now combine and analyse information from a variety of live stream sources.

By using DAS to monitor depots and lengthy stretches of track, patrolling security teams could be restructured to act as rapid response taskforces. Equipped with real time camera devices, these operatives would be deployed to investigate any disturbances detected by the system and transmit a live stream of visual information back to a centrally located hub. This central control centre would then assess the visual evidence alongside the data received from the DAS cables to determine the level of risk and, if deemed sufficiently serious, coordinate the deployment of additional resources.

DAS could prove a boon for the protection of line-side services. The number of metal thefts from railways has decreased rapidly during recent years, largely thanks to the 2013 Scrap Metal Dealers Act, but track side location cabinets and REBs (relocatable equipment buildings), which house vital signalling, telecommunications and power equipment, remain vulnerable to vandalism, sabotage and even terrorist attack.

Looking beyond the security sphere, DAS could be used to inform planned and reactive maintenance programmes – for example, by alerting teams to the change in vibration caused by wheel flats – as well as offering safety applications. DAS is already being employed as an early warning system for rock falls along the landslide prone Glasgow-Oban line. With Britain’s stormy weather reported to be on the rise, distributed acoustic sensing’s ability to detect fallen objects such as tree branches could become increasingly important.

Setting the parameters
As with many new technologies there are a number of caveats to keep in mind.

The technology is extremely sensitive and can pick up the lightest of vibrations and movements. Disturbance events are likely to be detected regularly. To avoid wasting resources and time, rigorous systems need to be put in place to ensure that the number of false alarms is kept to a minimum.

Partly this is about configuring the technology correctly. Warning alerts need to be calibrated so that, for example, a fox running along a track is not highlighted as a potential threat. Of course, it can be difficult to differentiate between wildlife and human activity. This is where using multiple information sources and training becomes important.

Monitoring teams need to be able to interpret patterns in the data and make an informed decision based on an assessment of all the information at their disposal; generally speaking, frequent events such as heavy traffic passing along a carriageway close to a rail line will have a recognisable vibration signature and can thus be discounted as a threat.

The technology is only as good as the response of the monitoring teams. With alerts being generated in realtime, employees need to be able to react quickly, night and day. It is no good using distributed acoustic sensing to detect vandalism if by the time security teams arrive on site the criminals are long gone. Likewise, different teams need to communicate with each other, with maintenance teams alerting monitors of any planned activity to avoid false alerts.

With great power…
Like most new digital technologies, DAS systems will generate huge amounts of sensitive information – all of which will need to be securely stored.

We are now much more alert to the issue of cybersecurity, and as our thinking on this subject evolves businesses will be in a much better position to protect their data. At Interserve, we are accredited to ISO27001 information security standard. This is a good first step but organisations will need specific protocols in place to safely hold the database of information created by DAS.

With the potential to inform criminal prosecutions, it will be crucial to ensure that the data is stored in a standardised way and is of sufficient quality that it can be used and understood by a variety of different parties – whether legal teams or police officers. We are also looking at developing a dashboard system that would facilitate access to the information on a section by section basis for approved users.

Perhaps most tantalising, is the potential to use the data not just to identify current disturbances but predict future ones. With advances in analytics, teams will be able to distinguish activity hotspots and address any gaps in the security provision at the most vulnerable locations.

A word of caution
So why is the rail sector not rushing to embrace this seemingly miraculous technology?

Distributed acoustic sensing is in use by Deutsche Bahn and in the United States, and there have been some trials across the UK – but not to the extent one might expect.

Partly this is due to past limitations of the technology. Until recently, it remained a challenge to achieve bandwidth capable of handling such large quantities of real-time data at the speeds required to be effective. The technology has now caught up and, with the costs of live streaming falling, has become much more competitive.

There is also an element of the fear of the unknown. DAS requires unfamiliar technologies and new ways of working. Understandably, operators and their supply chain are not always willing to make an initial up-front investment on unproven technologies, even if the long-term benefits could and probably will be significant.

In the field of security, service providers face high employee turnover rates that present difficulties when it comes to investing in the training needed to make DAS effective. Providers need to be able to invest in their employees and know that they will retain that expertise within the business.

Looking forward
Distributed acoustic sensing is not a ‘fire and forget’ solution. It will require the commitment and investment of transport operators and their support partners as well as a crucial willingness to try something new. There will of course be teething issues as the parameters for monitoring are fine-tuned and teams receive training to be able to interpret and correctly categorise the data.

The potential, however, is massive, and it is clear from other industries that this technology can be used effectively. As the capacity of Britain’s railways continues to expand to meet rising demand, distributed acoustic sensing could provide a cost-effective means of monitoring our growing railways.