**Scientists Use Fiber Optic Cables to Listen to Cicadas**
*New Technology for an Unlikely Application*
One of the world’s most peculiar test beds stretches above Princeton, New Jersey. It’s a fiber optic cable strung between three utility poles that then runs underground before feeding into an “interrogator.” This device fires a laser through the cable and analyzes the light that bounces back. It can pick up tiny perturbations in that light caused by seismic activity or even loud sounds, like from a passing ambulance. It’s a newfangled technique known as distributed acoustic sensing, or DAS.
**New Use for DAS**
DAS can track seismicity, and scientists are increasingly using it to monitor earthquakes and volcanic activity. But the scientists in Princeton just stumbled upon a rather … noisier use of the technology. In the spring of 2021, Sarper Ozharar, a physicist at NEC Laboratories, noticed a strange signal in the DAS data. “We realized there were some weird things happening,” says Ozharar. “Something that shouldn’t be there. There was a distinct frequency buzzing everywhere.”
**Unlikely Discovery**
The team suspected the “something” wasn’t a rumbling volcano in New Jersey, but the cacophony of the giant swarm of cicadas that had just emerged from underground, a population known as Brood X. A colleague suggested reaching out to Jessica Ware, an entomologist and cicada expert at the American Museum of Natural History, to confirm it. When Sarper and the team showed that you could actually hear the volume of the cicadas, and it kind of matched their patterns, I was really excited,” says Ware.
**Insects and DAS**
Add insects to the quickly growing list of things DAS can spy on. Thanks to some specialized anatomy, cicadas are the loudest insects on the planet, but all sorts of other six-legged species make a lot of noise, like crickets and grasshoppers. With fiber optic cables, entomologists might have stumbled upon a powerful new way to cheaply and constantly listen in on species—from afar.
**DAS Technology**
DAS is all about vibrations, whether they be the sounds of a singing brood of cicadas or the shifting of a geologic fault. Fiber optic cables transmit information, like high-speed internet, by firing pulses of light. Scientists can use an interrogator device to shine a laser down a cable and then analyze the tiny amounts of light that bounce back to the source. Because the speed of light is a known constant, they can pinpoint where along the cable a given disturbance happens: If something jostles the cable 100 feet down, the light will take slightly longer to return to the interrogator than something that happens at 50 feet. “Every 1 meter of fiber, more or less, we can turn it into a kind of microphone,” says Ozharar.
The discovery of the use of DAS technology to detect the presence and patterns of cicadas has opened new doors of opportunity for entomologists and researchers interested in understanding and monitoring different species. With its ability to turn fiber optic cables into microphones, DAS could revolutionize the way insects and other natural phenomena are studied and observed.
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