Parametric Inversion of Brillouin spectra using L-curve criterion to enhance the accuracy of distributed strain measurement

International audienceTo ensure stability and durability of engineering structure in natural soil, optical fiber sensors have gained interest over last decade. In addition to conventional geophysical sensors, Brillouin spectra based sensor enables to perform distributed strain measurement. Its algorithm performs a strain measurement with a 40cm spatial sampling over several kilometers. The monitoring of engineering installations needs a centimeter spatial sampling and a better strain accuracy. Previous works highlighted that the industrialized algorithm has great limitation for the exploitation of the local information contained into Brillouin spectra. Indeed, based on its asymmetry and broadening, it is possible to estimate local Brillouin frequencies with a better strain accuracy. We propose here to apply a parametric inverse method using L-curve criterion to estimate the strain with a 5cm spatial sampling. To validate this method, a one-to-one scale experiment has been implemented by optical fiber cable at several depths. Comparing the distributed strain provided by the Brillouin based sensor and our algorithm with a reference strain sensor, the proposed algorithm successfully fulfills the combination of a 5cm spatial sampling over kilometers and a high strain accuracy