DAS or Distributed Acoustic Sensors (DAS) are a revolutionary photonic sensing technology that convert standard communications fibre into a linear array of discrete vibration sensors. Activities such as people hot-tapping pipelines, leaks, perimeter intrusions, moving vehicles, industrial operations, failing mechanical components, and so many more all generate vibrations with distinct acoustic characteristics. DAS technology monitors these vibrations, and if supported by the right software accurately detects, classifies and reports on the vibration events – locating the position of each event to within a few metres.
A DAS is an advanced variant of an Optical Time Domain Reflectometer (OTDR) that monitors the coherent Rayleigh backscatter noise signature in a fibre optic cable as pulsed light is sent into the fibre. The coherent Rayleigh noise generates fine structure in the backscatter signature of the fibre cable. The DAS focuses on the Raleigh component to increase its prominence in the backscatter trace.
DAS is optimised to measure small changes in the coherent Rayleigh noise structure that occurs from pulse to pulse. Since the coherent Rayleigh noise structure is generated interferometrically within the fibre by the relative locations and strengths of local scattering centres intrinsic to the structure of the glass, very small physical (acoustic or vibration) disturbances at a point in the fibre can make detectable changes in the interferometric signal.
DAS operates with standard telecommunications grade optical fibres. These optical fibres can be installed as an asset is being built, with DAS in mind (e.g. a pipeline), or retrospectively on existing telecommunications infrastructure – such as the ubiquitous fibre networks in our urban areas. DAS uses optical fibres as the ‘sensor’, the DAS itself being the interrogator of the returning backscatter signal. Therefore by using DAS you use a ‘sensor’ that is immune to EM or RF interface – is also inert and requires no power along the entire length beyond the DAS interrogator. And, depending on the quality of fibre (among other environmental attributes), means that 50km of optical fibre can be monitored by one interrogator on a single channel. As a result a DAS monitoring solution can often be installed more quickly (than some traditional monitoring technologies), at a lower deployment costs, and therefore result in a considerable reduction in “through life” and maintenance costs.
The applications of DAS technologies are numerous – the value of acquired information being very dependent on the software it is combined with to accurately identify, classify, and alarm on backscatter events. Many forward thinking organisations facing significant challenges, whether distance, environment or cost related, have been the first to benefit from DAS based solutions. Now a range of markets continue to enhance their operations and protect their operations:
Upstream/Midstream/Downstream asset monitoring and performance enhancement
Transport tracking and health monitoring (e.g. trains, failing infrastructure, congestion)
Smart City asset monitoring
With optical fibres common place in our environments, the potential of DAS based solutions is only just being realised – the opportunities for its use are limitless.
DAS is an adaptable fibre enabled technology capable of providing an invaluable layer of intelligence for a range markets and applications. Fotech continues to push the boundaries of Distributed Acoustic Sensing – and with our fibre enabled platform solutions, combining our cutting edge photonics, advanced AI and edge computing we continue to successfully meet challenges faced by our markets and customers.Products & Solutions