RESEARCH conducted by Frauscher Sensor Technology into fibre sensing technologies and their viability for rail showed that Distributed Acoustic Sensing (DAS) has the potential to become the base technology for train tracking, asset condition monitoring and security applications.

FrauscherFrauscher has now developed the DAS technology together with its axle counting and wheel detection systems into a suite of products called Frauscher Tracking Solutions (FTS). Since its initial presentation at InnoTrans 2016 in Berlin, the company has been developing the system together with railways, partners and research institutes.

DAS works by sending a light pulse into a glass fibre where millions of minor changes, each of which scatters a small portion of the light pulse back towards the laser emission site. These reflection sites are called scatter sites and the reflected component of the scattered light is called backscatter.

At the opposite end of the fibre the laser pulse is absorbed by a termination unit, preventing a large reflection back to the detector. Sound waves and vibrations affecting a point along the fibre cause small changes in the light reflected from the scatter sites. By evaluating the changes of the backscatter, the whole fibre optic cable turns into a continuous sensor that works like a string of virtual microphones.

As the light pulse and backscatter are travelling at the speed of light, changes detected in the backscatter caused by various sound sources can be translated into acoustic signatures.

By developing appropriate algorithms, it is possible to connect these signatures to specific events. Using this method, it is possible to detect people walking, trains moving, and changes in asset condition, as all of these create certain levels and patterns of acoustic energy.

It was apparent during initial test installations that DAS provided a wide range of benefits. But just like any other sensing technology, it has a specific set of challenges to overcome.

In its current form, DAS cannot identify which track a train is travelling on along a multi-track line. While the cable senses all the trains and their movements on all tracks, it still requires a secondary input to corroborate which track the acoustic signature is associated with.

With FTS, Frauscher has integrated DAS with axle counters and wheel sensors to overcome some of its constraints, enabling application of the technology on a double-track line.

On a stand-alone basis, FTS provides real-time information of a train’s position, speed, acceleration, and length, but when it is combined with wheel detection systems or axle counters, these can take care of fail-safe track vacancy detection up to SIL 4, while FTS can generate additional information that can be used to optimise train movements.

By combining inductive sensors with DAS, FTS can offer railways numerous new possibilities for data generation. Implementing data from the railway’s other systems can improve the quality of the information even further, but this also places special demands on interfaces and data formats. In test installations so far, various applications have already been implemented in train detection, infrastructure monitoring and safety applications.


FTS makes it possible to locate all trains within a monitored track section in real-time. In non-safety-relevant areas, FTS can also be used as a stand-alone solution. Since no specific equipment needs to be fitted to the vehicles, their design and origin are irrelevant.

In remote areas, FTS can provide a cost-effective solution for control systems. Integrating an axle counter makes it possible to combine DAS-based real-time tracking of trains with safety-relevant applications, while associated interfaces can control level crossings. A Traffic Management System (TMS) can combine inputs from both systems and calculate accurate times of arrival, supply platform displays or coordinate and compose station platform announcements.

When monitoring the condition of infrastructure and train components, FTS can supplement or even reduce the amount of lineside equipment. For example, it can identify wheel flats or broken rails based on acoustic signatures. Rock falls can also be located, and the corresponding information forwarded directly via radio to approaching trains. If data from FTS and a wheel detection system is overlaid, certain incidents can be localised accurately along the route, while integrating information from the operator’s different databases can enrich this data pool even further. If train numbers are used, wheel flat alarms can be assigned to a specific train and axle via the wheel detection system.

DAS also has the potential to deliver a dynamic view and real-time awareness of infrastructure health, which in turn allows for the use of immediate, short and long-term preventative and predictive maintenance actions.


The oil and gas industry uses DAS for a range of safety applications, so adapting the corresponding algorithms for rail applications was one of the first steps taken when developing FTS. This can detect people and animals on or off the track. It also enables the implementation of various safety applications, such as the detection of vandalism or cable theft.

Passing on data and linking it with additional information further increases the application’s potential. Interfaces to safety equipment can provide alarm messages by email or SMS. It can also accurately locate work crews and provide individuals with information, for example about approaching trains, via a direct connection on mobile devices. The system can even supply drones with data which is then used to fly the drone directly to the section in question.

Frauscher claims that it is the first dedicated supplier within the railway industry to combine DAS with proven wheel detection systems and axle counters. “This exciting and proven technology opens up a wide range of applications with the capability to track trains, monitor asset condition, secure infrastructure and protect personnel in real time using one single solution,” says Mr Michael Thiel, Frauscher’s CEO. “Integrating DAS with proven railway technologies such as axle counters or wheel detection systems significantly improves the way trains are tracked unlike any other existing technology and will lead to a revolution in railway operation.

“However, we do not see this as a threat to our core business; quite the contrary. Next to ETCS, CBTC and maybe PTC in the United States, axle counting and wheel detection based on inductive sensor technology has been one of the fastest growing and most requested technologies in railway signalling and automation.”

Thiel says Frauscher has been growing by more than 15% per annum during the last few years, and he expects this trend to continue. “For sure, this is accompanied by increasing competition with new companies entering the market providing axle counting technology,” he says. “In parallel to this, existing players are also launching new or adapted products, but this also shows that the market for axle counting and wheel detection is still growing, and we expect it to grow even faster in the next few years.”