One of the world’s most unusual test benches stretches above Princeton, New Jersey. This is a fiber optic cable strung between three utility poles, which runs underground and then connects to an “interrogator”. The device fires a laser through a cable and analyzes the reflected light. It can pick up small fluctuations in light caused by seismic activity and even loud sounds like a passing ambulance. This is a new technology known as Distributed Acoustic Sensing (DAS).
Because DAS can track seismic activity, other scientists are increasingly using it to monitor earthquakes and volcanic activity. (In fact, buried systems are so sensitive that they can detect people walking or driving over them.) But Princeton scientists have discovered some rather…noisier uses for this technology. I came across it by chance. In the spring of 2021, Sarper Ozaler, a physicist at his NEC laboratory that runs the Princeton testbed, noticed that: Strange signals in DAS data. “We realized something strange was happening,” Ozaral said. “It shouldn’t be there. A unique frequency was buzzing everywhere.”
The research team suspected that the “something” was not a rumbling volcano. new jersey— but the cacophony of a huge swarm of cicadas known as Brood-X that has just emerged from underground. A colleague suggested I contact Jessica Ware, an entomologist and cicada expert at the American Museum of Natural History, to find out. “I was watching cicadas and was going around Princeton collecting cicadas for biological samples,” Ware says. “So when Sarper and the team showed what they could actually do; listen I was very excited because the sounds of the cicadas and their patterns matched somehow. ”
Insects join the rapidly growing list of things that DAS can monitor. Thanks to their specialized anatomy, cicadas are the noisiest insects on the planet, but all kinds of other six-legged species, like crickets and grasshoppers, also make loud noises. Entomologists may have stumbled upon a powerful new way to constantly monitor species from a distance using fiber optic cables. “One of the challenges we face now that insect populations are in decline is the need to collect data about how big the population is and which insects are where.” Ware says Mr. “I think this type of remote he can be really creative once he understands what he can do with sensing.”
DAS is all about vibrations, such as the sound of cicadas or the movement of geological faults. Fiber optic cables transmit information by firing pulses of light, much like high-speed internet. Scientists can use an interrogation device to shine a laser into the cable and analyze the tiny amount of light that bounces back to the light source. Since the speed of light is a known constant, it is possible to determine exactly where a particular disturbance occurs along the cable. If something hits the cable at 100 feet, the light will take slightly longer to return to the interrogator than if it occurred at 50 feet. “The fiber allows him to turn every meter more or less into a kind of microphone,” Ozalal says.
