Distributed Optical Fiber Sensing System For The Subway Tunnel Monitoring

The subway tunnel is an infrastructure with long service period. The structural cracks and leakage of the tunnel will be a threat to life safety and cause the economic loss. This paper focuses on the distributed optical fiber sensing technology for metro tunnel monitoring system.The development of distributed optical fiber sensing technologies were analyzed and compared firstly in this paper, which mainly focused on the Brillouin optical time-domain reflectometry(BOTDR) technology. Secondly, the mechanism of Brillouin scattering sensing was investigated and the FFT and Mallat wavelet algorithms to extract the Brillouin frequency shift signal were used. Finally, simulation of the system was realized by LabVIEW platform and a satisfactory result has been obtained.The main work of this paper summarizes as following:A VI program was designed for BOTDR sensing system and the simulation results were compared to the actual situation with very small error, which show that the virtual monitoring system is an ideal one for real applications.A new and stable event structure was employed in our program which improved the running efficiency greatly. The program also has an unique function for data collection and storage through LabVIEW and Access database connection.A FFT and a wavelet algorithms for spectrum analysis of Brillouin frequency shift signal in BOTDR sensing system were established. The comparison of the two algorithms were made, and the helpful result has been obtained that the Mallat wavelet algorithm can extract the Brillouin scattering signal characteristics more accurately than FFT method.