Listening Beneath the Surface: Fibre Optic Distributed Sensing on Campus
What if fibre optic cables could do more than deliver our high-speed internet? What if they could also help us listen to the Earth, capturing the subtle seismic whispers and temperature shifts happening deep beneath our feet?
That’s the idea behind fibre optic distributed sensing - a technology that turns standard optic cables into a dense network of sensors monitoring changes in sound, temperature, and pressure underground.
Distributed Acoustic and Temperature Sensing on Campus
Fibre optic distributed sensing is at the heart of an exciting project at the University of Leeds, exploring how ground-source heat can be harnessed to warm and cool campus buildings.
In early 2024, several boreholes were drilled as part of the University's efforts to decarbonise the campus.
These boreholes, reaching depths of up to 250 metres, enabled a group of researchers from Geosolutions Leeds to explore whether local sandstone layers, specifically the Elland Flags and Rough Rock formations, can be used as geothermal reservoirs.
Alongside other monitoring tools, the research team installed fibre optic cables down the boreholes to explore the potential of novel distributed acoustic and temperature sensing (DAS and DTS) methods.
Painstaking measurement of fibre optic cable ahead of borehole deployment.
During initial surveys in autumn 2024, the team generated waves, called seismic signals, that were detectable with DAS along the entire 250-metre-deep cable.
The distributed acoustic sensing also allows the speed at which seismic waves travel through the rocks, known as seismic velocity, to be estimated down to depths of around 200 metres.
Left: Seismic signals recorded with DAS, visible to depths of 250 m. Right: By timing how long it takes energy to reach a particular depths, it is possible to track the variation of seismic velocity with depth. Heating could cause these velocities to change, allowing the geothermal system to be monitored.
Why is this important?
As the geothermal system on campus is developed and used, the heat could change and with help from other techniques, the ongoing DAS monitoring could detect the subtle changes underground, helping ensure the geothermal system operates efficiently and safely.
Tracking how seismic signals move through the underground reservoir is important because it can reveal useful information like changes in water or temperature, similarities in rock layers between different boreholes, and signs of underground movement. This would help us reduce risk during geothermal energy production by allowing us to monitor the evolution of the aquifer and assess the sustainability of the geothermal system.
Looking ahead, the true potential of DAS lies in what it can reveal over time.
Permanent DAS installations are making it possible to monitor the Earth in a way that’s more detailed than ever before, bridging the gap between field- and lab-scale analysis. At Leeds, it is helping researchers unlock clean energy from the ground up and showing how tomorrow’s sensing technology can make a real-world impact today.
The University of Leeds operates Febus Optics Distirbuted Sensing Systems on campus, instrumentation which is available for research and industry collaboration.