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Distributed fibre-optic sensing (DAS/DTS)
A single optical fibre turned into thousands of measurement points along a pipeline, well, cable or perimeter. Temperature sensing is long established; acoustic sensing for leak and intrusion detection is in production, but its performance depends heavily on installation and signal interpretation.
How a fibre becomes a sensor
An interrogator at one end of the fibre sends laser pulses and analyses the tiny fraction of light scattered back from every point along it. Because the speed of light in the fibre is known, the time of arrival tells the interrogator where along the cable each signal came from, typically resolved to a few metres over many kilometres.
Different scattering effects measure different things. Raman scattering varies with temperature and is the basis of distributed temperature sensing (DTS). Brillouin scattering responds to temperature and strain and is used for distributed strain sensing (DSS), for example to detect ground movement. Rayleigh scattering, analysed coherently, responds to minute vibrations and is the basis of distributed acoustic sensing (DAS), which effectively turns the fibre into a long line of microphones.
| Technique | Physical effect | Measures | Typical industrial uses |
|---|---|---|---|
| DTS | Raman backscatter | Temperature | Power-cable hotspots, fire detection, well profiles, liquid leaks with thermal signature |
| DSS | Brillouin backscatter | Strain (and temperature) | Ground movement, pipeline and dam deformation |
| DAS | Rayleigh backscatter | Vibration and sound | Third-party intrusion, gas and liquid leaks, flow and pig tracking |
Where it is used
Power transmission is a well-documented example. France's transmission system operator RTE uses combined DAS and DTS on about 39 km of a 225 kV underground cable link to detect third-party intrusion and cable faults and to locate hotspots; the project team also simulated nearby agricultural activity such as soil mixing and harvesting to reduce false alarms 1. That last detail illustrates the central practical issue with DAS: the fibre hears everything, and the value lies in telling a real threat from a tractor.
Pipelines are the other main market, for leak detection, intrusion detection and integrity monitoring. Industry practitioners point out that DTS and DAS are the main options for leak detection, that the right choice depends on many variables, including product, pressure, burial and cable position, and that deploying both together is ideal but often ruled out by cost 2. Downhole, DTS and DAS are used in oil and gas wells for flow profiling and monitoring.
What controls performance
The research literature is a useful corrective to supplier brochures. In controlled tests at the Colorado School of Mines, reported in October 2025, DAS detected simulated leaks of a quarter-inch to one inch on a short steel test pipeline, with stronger signals for larger leaks, higher flow velocities and cables closer to the leak. Cable type and attachment made a large difference: lighter, flexible cables gave the clearest signatures, a thick cable showed limited sensitivity, and better taping improved an externally mounted cable 3. These were laboratory tests, not field results, and the authors identified machine learning to separate leak signatures from normal operating noise as future work 3.
The practical lessons for owners follow directly. Where the fibre sits relative to the pipe, how it is coupled to it, and how the signal processing is tuned to the specific route matter as much as the interrogator. A fibre laid for telecommunications in the same trench may be usable, but its sensitivity to leaks on the pipe will differ from a cable designed and placed for sensing.
Fitting it into operations
- Define what the system must detect, at what size and within what time, before choosing technology; that requirement drives the choice between DAS, DTS or both.
- Plan for a tuning period. False alarms from traffic, farming and construction along the route are normal at first and need structured review.
- Integrate alarms with the control room's existing leak-detection and response procedures rather than adding a separate screen nobody watches.
- Treat the interrogator and its data link as OT assets, with the same security and maintenance discipline as other monitoring systems.
Evidence timeline
- Nov 2021RTE deploys combined DAS and DTS on about 39 km of a 225 kV underground cable link. 1
- Apr 2024Pipeline Technology Conference paper: DAS and DTS are the main fibre options for leak detection; suitability depends on many variables. 2
- Oct 2025Colorado School of Mines laboratory tests show DAS leak detection depends strongly on cable type and coupling. 3
Why it sits at the Industry Acceptance stage
Distributed temperature sensing is long established, and combined DAS/DTS systems are in production with several owners and suppliers across power and pipelines, which supports evidence level E4 and placement at the Industry Acceptance stage.
We keep the entry at Industry Acceptance rather than Proven in Use because DAS leak detection performance is still highly installation-specific, independent field performance data is limited, and false-alarm management remains a significant operating burden.
Adoption signals to watch
- Published field performance data on leak detection: minimum leak size, time to detect and false-alarm rates.
- Regulators recognising fibre-optic leak detection explicitly in pipeline leak-detection requirements.
- Standardised machine-learning classification that reduces site-by-site tuning effort.
Questions to ask before committing
- What leak size and detection time must the system achieve, and has the supplier demonstrated that on a comparable installation?
- Where will the fibre sit relative to the pipe or cable, and how is it coupled?
- What false-alarm rate should we expect during the first year, and who reviews alarms?
- Does the route need DAS, DTS, or both?
- How do alarms reach the control room and the existing leak-response procedure?
Terms used on this page
- DAS
- Distributed acoustic sensing, based on Rayleigh backscatter.
- DTS
- Distributed temperature sensing, based on Raman backscatter.
- Interrogator
- The opto-electronic unit that launches the light and analyses what returns.
Sources
- Power cable monitoring solution to French electricity transmission system operator
- DFOS: what type of fiber optic sensing is most appropriate for leak detection on my pipeline?
- A practical distributed acoustic sensing approach for gas-pipeline-leak detection
Related technologies
See this entry on the full maturity map · All Instrumentation entries · How placements are made. Stage and time-horizon placements are editorial judgements based on the public sources listed above, as of October 2026. They are not engineering, safety or investment advice; see the Terms of Use.