A distributed fiber optic sensor system for dike monitoring using Brillouin frequency domain analysis

We report on the development of a distributed sensor system for strain measurement using Brillouin optical frequency domain analysis (BOFDA) in single-mode silica optical fibers. Our research aims at the application of the sensor system in flood protection. The sensing fibers are embedded into the soil body of river dikes, where they perform early detection of critical soil displacement. We present a BOFDA setup that performs strain measurements with a spatial resolution better than 3 meters over a length of 2 km. Its accuracy is verified by measurements on a calibrated strain profile as well as several laboratory tests that emulate the stressing of the optical fibers by soil movement. It is shown that the BOFDA approach offers feasible solutions to known critical issues of Brillouin sensing such as spectral broadening at high spatial resolution, digital filtering for enhancement of the dynamic range, and fluctuations of the Brillouin gain due to birefringence.