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Fiber-optic sensor reveals new details of Greenland glacier

18 May 2021

University of Cambridge takes detailed measurements of ice properties on the Greenland Ice Sheet.

A project led by the Scott Polar Research Institute at the University of Cambridge has used a fiber-optic sensor to gather new ice temperature data on a Greenland glacier.

The findings, published in Science Advances, represent the most detailed measurements of ice properties ever taken on the Greenland Ice Sheet, according to the team.

They also represent the first use of fiber-optic distributed temperature sensing (DTS) on the Greenland Ice Sheet, installed in a bore hole 1,043 meters deep.

Distributed sensing allows spatially resolved measurements of physical properties, in this case temperature, along the full length of a continuous optical fiber, rather than the discrete data from physically separated measuring devices that conventional thermometry would produce.

"We normally take measurements within the ice sheet by attaching sensors to a cable that we lower into a drilled borehole, but the observations we've made so far weren't giving us a complete picture of what’s happening," said Poul Christoffersen from the Scott Polar Research Institute.

"The more precise data we are able to gather, the clearer we can make that picture, which in turn will help us make more accurate predictions for the future of the ice sheet."

The new data form part of the European Responder project, carrying out hot-water drilling on the Sermeq Kujalleq glacier to improve understanding of the evolution of ice flow on the Greenland Ice Sheet, and employing multiple complementary technology platforms.

Distributed fiber-optic sensing has allowed Responder to combine temperature information with data relating to the physical sub-surface movement of ice, gathered at the same time through distributed acoustic sensing (DAS). DAS was used in 2020 by ETH Zurich to monitor glacier movements in Switzerland's Rhone Glacier, with probes positioned just under the snow's surface providing new data about the mechanics of the glacier's movements.

"Fibre-optic sensing enables measurements to be taken in a distributed manner over the entire 1-kilometer depth of the borehole with spatial accuracy ranging from 0.5-meters (DTS) to 10-meters (DAS)," commented Responder on its project site.

"Sections of the depth profile that would otherwise be unsampled can therefore be examined in extraordinary detail. The rapid development of fibre-optic sensing over the last decade means that this increase in spatial resolution does not damage the accuracy of the measurement. In many cases it is improved."

Transformative potential of high-resolution DTS in glacier studies

The project used a commercial DTS platform from Silixa, said to be the highest performance ruggedised distributed temperature sensor currently on the market according to the supplier.

"The DTS system consisted of a Silixa XT-DTS, armored cable housing fiber optics, and thermistors for calibration purposes," said the project in its published paper. "It works by measuring the temperature-sensitive components of Raman backscatter (Stokes and anti-Stokes wavelengths), and travel time, when a laser pulse is transmitted through the optical fiber."

Data from the fiber-optic system indicated that ice deformation and temperature, both vertically in borehole profiles and spatially within catchment areas of the glacier, exhibit greater heterogeneity than previously considered. This is valuable information for an understanding of both glacier movement and why the Greenland Ice Sheet is rapidly losing mass.

The results also demonstrate "the transformative potential of high-resolution DTS" in the field of glacier thermodynamics, according to the Institute team.

"This technology is a big advance in our ability to record spatial variations in ice temperature over long distances and at really high resolution," commented Bryn Hubbard of project partners the University of Aberystwyth.

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