Stretching out thousands of miles beneath our feet, our fibrous ears listen. When you walk or drive over buried optical fiber, ground activity creates unique vibrations that slightly disrupt the path that light travels down the cable. With the right equipment, scientists can analyze the disturbance and determine what the source was and when exactly it was wandering there.
This rapidly growing technology, known as distributed acoustic sensing (DAS), is so sensitive that researchers recently used it to monitor the cacophony of cicada mass emergence. Did. Some companies are using the cables as ultra-sensitive equipment to detect volcanic eruptions and earthquakes. Unlike traditional seismometers that are fixed in one location, the network of fiber optic cables covers the entire terrain, providing unprecedented detail of ground rumbling in different locations.
Scientists are currently experimenting with bringing DAS to a train near you. When a train travels over a section of track, it creates vibrations that analysts can monitor over time. If that signal suddenly changes, it could indicate a problem with the rail, such as a crack or a broken sleeper. Or if a landslide explodes across the tracks on a mountain pass, DAS might also “hear” it and alert the railway operator to a problem that was not yet noticed by the human eye. If the signal changes more slowly, defects in track alignment can occur.
Coincidentally, fiber optic cables are already being laid along many railways to connect all signaling equipment and for communications. “We can reduce costs because we use equipment and infrastructure that is already available for this,” says engineer Hossein Taheri. study Georgia Southern University’s DAS for Railroads. “Some railroads may not have fiber, so you have to lie down. But yes, most of them usually already have it.”
To use that fiber, you need a device called an interrogator, which fires laser pulses into the cable and analyzes the tiny bits of light that bounce back. So suppose a stone hits a railroad track 20 miles from the interrogator. This creates characteristic ground vibrations that disturb the optical fibers near the tracks and appear in the optical signal. Because the scientist knows the speed of light, he can accurately measure the time it takes for the signal to return to the interrogator and pinpoint the distance to the obstacle to within 10 meters, or about 30 feet. Masu.
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