HomeSignalling and TelecomsListening to the network - Fibre Optic Acoustic Sensing

Listening to the network – Fibre Optic Acoustic Sensing

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Rail Engineer first reported on Network Rail’s Fibre Optic Acoustic Sensing (FOAS) technology development in 2019. Now, two years later, Network Rail has announced the next stage in the concept’s development, with trial installations to be undertaken by a consortium led by Thales Ground Transportation Systems Ltd.

A fibre optic cable consists of one or more very fine strands of glass, each of similar thickness to a human hair and referred to as a fibre. The centre of each fibre is called the core, which provides the pathway for light to travel. The core is surrounded by a layer of glass called the cladding, which reflects light inward to avoid loss of signal and allow the light to efficiently pass-through bends in the cable.

Single-mode optical fibre networks often use Wave Division Multiplexing (WDM) techniques to increase the amount of data that each fibre can carry. WDM allows light at multiple different wavelengths to be multiplexed and de-multiplexed at the receiving end, effectively transmitting multiple communication paths through a single light pulse.

Noise detection

FOAS uses another characteristic of fibre. This is when light is reflected or ‘backscattered’ as it propagates through the fibre in response to a change in temperature, a bending or pulling force to the cable, or by mechanical waves in the fibre’s proximity. The backscattering is sensitive enough to detect noise, which is detected at the source, allowing the location and cause of the backscatter event to be determined.

In very simple terms, FOAS can be considered as a series of virtual microphones and sensors located every few metres along the track along the extensive network of fibre cable on most rail routes (there are around 20,000km of fibre cable running alongside Britain’s railways).

Under the Thales-led trial, the FOAS technology will incorporate data fusion to boost the ‘listening’ capabilities of optical fibres, which has the potential to enhance remote condition monitoring of assets and provide valuable data to enhance safety, improve train performance, and reduce disruption. The trial will also look at enhancing monitoring by incorporating smart CCTV technology where appropriate.

A design contest was launched by Network Rail in June 2020, in collaboration with Dutch rail infrastructure operator ProRail. This challenged over 40 suppliers to come up with proposals for a funded, 12-month, outcome-focused trial of FOAS, IoT sensors and smart CCTV cameras, amalgamated through intelligent data fusion and processing. The design contest also formed part of an existing agreement between Network Rail and ProRail to collaborate on research and development opportunities. The two companies signed a Memorandum of Understanding (MoU) in March 2019 with a commitment to work together and share expertise to solve challenges faced by the rail industry. The MOU will support the delivery of Network Rail’s £245 million R&D portfolio up to 2024, providing opportunities to jointly develop and transfer technologies into new operating environments over five years. Network Rail says it also plans to reduce barriers to innovation by making itself easier for partners to work with.

Experienced consortium

For the winning bid, Thales pulled together an impressive consortium with experienced companies familiar with state-of-the-art technology, and engineers who know the operational requirements of the rail industry and working on a live railway.

The consortium includes: The Austrian Institute of Technology (AIT), Austria’s largest research and technology organisation, which develops acoustic solutions for transport; Southampton-based Focus Sensors Ltd, experts in fibre optic sensors, having experience in the rail industry with their Indus™ Cloud platform; Dahua Technology, a world-leading video-centric smart CCTV and IoT solution and service provider, with 50 per cent of its 16,000 employees engaged in R&D; and Incremental Solutions, based in York. Incremental has a lot of experience with user intuitive, scalable systems in the rail industry, with products such as software systems employing Global Positioning System (GPS), geo-spatial analysis, and providing insights into vehicle performance that have historically been unachievable. Thales will use its own technology experts located in Reading and Cheadle Heath, Stockport, and throughout the country.

EEMC Monitors Ltd, Comms365 Ltd and MPEC Technology Ltd are not formally part of the consortium but are providing hardware and data services to the project. EEMC Monitors Ltd are the sole specialist UK and Ireland distributor for the Swarm Vibration Monitor and Honeycomb Cloud Monitoring Platform developed and manufactured by Dutch Innovators Omnidots BV. Comms365 are specialists in internet connectivity solutions and will be providing a multi-site wireless network for sensor driven data collection. MPEC are already involved in the rail industry and provide hardware and software solutions for reactive, condition based and predictive maintenance of signalling assets.

Operational challenges

The consortium will address four operationally challenging user case areas for FOAS: train movement and position reporting; rail and wheel defects; level crossing safety management; and detecting trespass and people on the trackside.

Network Rail say that the FOAS development and trial is an excellent example of collaboration, co-operation and teamwork, with all the members of the consortium enthusiastically working together and supporting one another to achieve the project’s outcome-focused objectives.

The trial work will be conducted at Network Rail’s Rail Innovation & Development Centre (RIDC) Melton test track, also known as the Old Dalby Innovation Centre, and on the mainline railway from Melton Mowbray to Leicester. This allows the trials to be undertaken both on and off the operational railway, with a number of level crossings available on the main line. Work has already started and will continue through to Autumn 2022. This will enable the trials to be undertaken throughout the year, in a wide range of temperatures, with seasonal variation of light and rail use.

Thales’ winning bid represents an efficient approach to innovation by using existing infrastructure to deliver new capabilities while avoiding installation costs, as no new fibre cables will be installed. There will be no interference or risk to the operational data carried by the fibre cables, as FOAS will use spare ‘dark’ fibres. Most fibre cables on the network consist of 24 individual fibres, although Network Rail are installing 432 fibre cables as part of its Trackside Connect Services programme. This allows interested parties, such as private telecoms operators, internet service providers and other organisations, to lease dark fibre for their own commercial purposes.

Usually, a pair of fibres are required for a telecoms link: one to transmit and one to receive. But the data-carrying capability of fibres are enormous. Each fibre is capable of transmitting light at 186,000 miles per second, with one fibre carrying a light signal powerful enough to stream 1.5 million YouTube videos at once. For example, 10 WDM channels on a single fibre, each streaming 1.5 million videos, multiplied by 432 fibres means the cable could carry more than 6 billion videos at once. Therefore, dedicating one fibre for FOAS per cable on any part of the railway should not be a problem, and the potential operational benefits of FOAS to the rail industry are enormous.


The key objective of the trial is to allow Network Rail to evaluate how the technology can benefit rail customers. In addition to the initial four main use cases, it could, in future, be used in many other ways, for example: to detect earthwork failures, train integrity, point machine defects, and in weather detection.

The FOAS data could also be a valuable feed into the Rail Data Marketplace (RDM). The £5 million funding package to improve rail travel for passengers was announced by the Government in June. It will provide a platform to share rail data across the industry, enabling a step towards a future data-driven railway. The platform is expected to create new opportunities for developers and technology companies to use the rail data and create passenger-facing applications and help in developing new services. RDM will provide passenger information to include seat availability, detail on disruptions and availability of facilities such as lifts and escalators, which will be integrated at one place.

Sharing rail data opens up new and exciting possibilities for apps and websites that can make taking a train a smoother, quicker and better experience. But RDM will need accurate data from across the network which is where FOAS could also help, by gathering data using the existing fibre optic network.

Paul Darlington CEng FIET FIRSE
Paul Darlington CEng FIET FIRSE

Signalling and telecommunications, cyber security, level crossings

Paul Darlington joined British Rail as a trainee telecoms technician in September 1975. He became an instructor in telecommunications and moved to the telecoms project office in Birmingham, where he was involved in designing customer information systems and radio schemes. By the time of privatisation, he was a project engineer with BR Telecommunications Ltd, responsible for the implementation of telecommunication schemes included Merseyrail IECC resignalling.

With the inception of Railtrack, Paul moved to Manchester as the telecoms engineer for the North West. He was, for a time, the engineering manager responsible for coordinating all the multi-functional engineering disciplines in the North West Zone.

His next role was head of telecommunications for Network Rail in London, where the foundations for Network Rail Telecoms and the IP network now known as FTNx were put in place. He then moved back to Manchester as the signalling route asset manager for LNW North and led the control period 5 signalling renewals planning. He also continued as chair of the safety review panel for the national GSM-R programme.

After a 37-year career in the rail industry, Paul retired in October 2012 and, as well as writing for Rail Engineer, is the managing editor of IRSE News.


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