fiber optic cable

Buried fiber-optic cable doubles as roadway sensor

Researchers are studying ways to use existing fiber-optic cables as distributed sensors to collect data on city road conditions.

Verizon and NEC recently conducted a proof-of-concept field trial in Richardson, Texas, during which they put an accelerometer on a rental car and drove it along a highway service road. The nearby fiber-optic cables acted as optical sensors that collected data based on vibrations from vehicles on the road, and NEC’s artificial intelligence software made sense of that data, classifying it into measurements of vehicle size, direction and speed of travel, and acceleration and deceleration.

Using fiber as optical sensors isn’t new, said Glenn Wellbrock, Verizon’s director of optical transport planning, but what makes this particular case unique is the use of standard transmission fiber. Typically, specialty fiber is used with purposeful gradings and placed around a specific perimeter, such as a military base.

“Nobody’s going to build specialty fiber all over the place, and we have lots and lots of fiber,” Wellbrock said. “We’re putting in 1,400 route miles of new cable every month -- that’s a lot of fiber going into the ground. What are some other things we might be able to do with it? That’s how we came to this testing.”

For the proof of concept, his team chose at random a single strand of fiber-optic cable in a standard buffer tube buried 3 feet underground and sitting 20 to 25 feet off the service road. The 432-count fiber cable was installed throughout the Dallas-Ft. Worth area almost two decades ago and carries typical customer traffic throughout the area, including a Verizon lab there.

Initially, Verizon began measuring vibrations near the installation to monitor the health of the cable -- to ensure, for instance, that no one was digging too close to it. The team noticed that they were able to pick up data on traffic on a service road, and with more than 95% accuracy, they could detect how many vehicles passed that point, their speed and their size.

When they also discovered about 150 feet of aerial cable that was installed by nearby construction workers who were building a road, they realized that the data could be used for more than monitoring the cable’s health. For instance, with both aerial and buried cables, they can measure day-to-night air temperature changes and sound vibrations such as gunshots, which have a sharp, unique signature.

“It’s an optical time-domain reflectometer, which means you fire a short pulse of light into the fiber and you listen for reflections,” Wellbrock said. “The longer you listen means the further away that reflection was. The fiber becomes a contiguous sensor, if you will.” That differs from specialty installations for which people get readings from pre-determined spots, he added.

AI tools such as convolutional neural networks and software vector machines helped optimize the distributed intelligent traffic informatics. The sensor system evaluated properties of back-scattering light, which can be used to derive static and dynamic strain, acoustics, vibrations and temperatures for each fiber segment. That lets users identify selected signatures and translate them into actionable information.

Besides detecting gunshots, potential use cases include monitoring roads for damage. For instance, during the field test, the team was able to pinpoint a hazardous pothole by combining data from the accelerometer, the car’s GPS and the fiber. Because the sensing capabilities can indicate whether a road is smooth, slightly bumpy or severely rough, the data could be used by city transportation departments to keep roads safe and operational.

“This test marks an important milestone for technology that could provide a huge leap forward for those building smart cities and those tasked to manage them,” Adam Koeppe, Verizon senior vice president of technology planning and development, said in a statement. “Instead of ripping up tarmac to place road and traffic-sensing technology, cities will be able to simply piggyback Verizon’s existing fiber-optic network.”

So far, the company hasn’t worked with any cities on specific projects. It’s still in the process of determining what it can measure and how accurately, but Wellbrock said the product development team is looking into ways the data can benefit smart cities. He expects to be able to start pilot tests with cities in the first half of next year.

The project is similar to one at the Lawrence Berkeley National Lab in California, where researchers use dark -- or unused -- fiber to measure seismic signals and saw the potential for also using it to monitor road conditions.

About the Author

Stephanie Kanowitz is a freelance writer based in northern Virginia.

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