Measurement error modification of linear non-uniform strain for BOTDA and a case study

The distributed Brillouin optical fiber sensor, which is a powerful tool in civil structural health monitoring, can obtain continuous strain or temperature distribution with exceptional high spatial resolution and accuracy. But in practice, the strain distribution is rarely uniform, the non-uniform components can lead to inaccuracies in the measurement results. In this paper, we proposed a modification method for non-uniform strain for distributed Brillouin sensing by studying the characteristics of the Brillouin Gain Spectrum (BGS) under typical linear cases of non-uniform distributions. A novel BGS width change based approach was used to reduce the non-uniform strain measurement errors and reconstruct the accurate strain distributions. The proposed method was validated by the load test monitoring data of a wind turbine blade. The strain distribution contained obvious no-uniform strain components. Comparisons of the measured accurate strain distribution and the reconstructed results show that the new approach is capable of modifying non-uniform strain measurement and decreasing the measurement inaccuracies in the distributed BOTDA sensing.