It’s like radar, but with light. Distributed acoustic sensing — DAS — picks up tremors from volcanoes, quaking ice and deep-sea faults, as well as traffic rumbles and whale calls.
Andreas Fichtner strips a cable of its protective sheath, exposing a glass core thinner than a hair — a fragile, 4-kilometer-long fiber that’s about to be fused to another. It’s a fiddly task better suited to a lab, but Fichtner and his colleague Sara Klaasen are doing it atop a windy, frigid ice sheet.
Fichtner, a geophysicist at the Swiss Federal Institute of Technology in Zurich, is one of a cadre of researchers using fiber optics to take the pulse of our planet. Much of this work is being done in remote places, from the tops of volcanoes to the bottoms of the seas, where traditional monitoring is too costly or difficult. There, in the last five years, fiber optics have started to shed light on seismic rumblings, ocean currents and even animal behaviors.
An optical fiber for DAS typically stretches several to tens of kilometers, and it moves or bends in response to disturbances in the environment. “It wiggles as cars go by, as earthquakes happen, as tectonic plates move,” says earth scientist Nate Lindsey, coauthor of a 2021 article. Those wiggles change the reflected light signal and allow researchers to tease out information such as how an earthquake bent a cable at a certain point.
Fichtner’s team buried their fiber-optic cable on Grímsvötn. In this video, they are trenching the first few hundred meters with a chainsaw because this part of the caldera rim is too steep for their snow-grooming vehicle.“The ability to just go under the seafloor for tens of kilometers — it is remarkable that you can do that,” Lindsey says. “Historically, deploying one sensor on the seafloor can cost $10 million.
In 2016, Marra’s team sought a way to compare the timekeeping of ultraprecise atomic clocks at distant spots around Europe. Satellite communications are too slow for this job, so the researchers turned to buried optical cables instead. At first, it didn’t work: Environmental disturbances introduced too much noise into the messages that the team sent along the cables. But the scientists sensed an opportunity.
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