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Researchers Develop Glacier Monitoring Tool Using Optical Fibers

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Swiss National Science Foundation professor Fabian Walter has come up with a new glacier monitoring tool in the form of optical fibers. The fibers are capable of monitoring entire glaciers.

Due to seismometers’ difficulty being installed in glacial areas, seismic monitoring coverage of glaciers is inconsistent. In a recent study, Walter demonstrated that it is also possible to monitor glaciers using optical fibers. Not only are the fibers easier to install than seismometers, but they also offer more measuring points. These fibers represent a way of extending seismic monitoring coverage in areas that are difficult to access.

Five days during March 2019, two teams led by Walter and Andreas Fichtner, a specialist in seismology and wave physics at ETH Zurich, recorded micro-earthquakes using a 1-km fiber optic cable installed a few centimeters within the snow cover on the surface of the Rhône Glacier. Distributed acoustic sensing was used to record disturbances in the optical signal at regular intervals of several meters along the cable. The recordings were then converted into seismograms.

In his study, Walter reported that having 500 sensors across the same monitoring area of the 1-km cable meant that the data contained more information than those from seismometers, particularly in localizing rockfalls and icequakes. Moreover, the cable delivered a better understanding of the jerky stick-slip movements by which the glacier moves. New types of seismic waves were identified, something that had not previously been possible with seismometers. Jerky movements of this type were already known to occur in the ice sheets of Greenland and Antarctica, but this was the first time their existence was rigorously verified in the Alps.

Optical fibers are already used to monitor earthquakes in certain settings, but Walter is one of the first scientists to work with this technology on glaciers.

“There are other teams already working on the subject, in Alaska, for example, because fiber optic technology offers benefits in this type of challenging environment,” Walter said. “It often takes several hours to install a seismological station capable of covering only a tiny part of a glacier. All we have to do now is lay out the cable and we have hundreds of sensors. In theory, the technology enables us to cover and monitor entire glaciers.”

By measuring seismic velocities, the fiber optic cable also yields additional information, such as details of the composition of the ice. It also enables scientists to measure ice deformation rates and understand the process by which crevasses form.

Other applications remain to be tested outside glacier zones. Optical fibers are already available alongside roads and railways and near to certain infrastructure installations. Optical fibers that have been installed but are not operational, known as dark fibers, could be used to monitor seismic events and prevent damage.

Photonics Spectra
Jul 2020
GLOSSARY
optical fiber
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote total internal reflection (TIR). It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.
Research & TechnologyEuropeSwitzerlandSwiss National Science Foundationopticsoptical fiberseismologyETH Zurichglaciersenvironmentfiber opticsTest & MeasurementTech Pulse

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