Real-time monitoring method for unauthorized working activities above the subway tunnel based on ultra-weak fiber Bragg grating vibration sensing array

Real-time monitoring of unauthorized working activities above the subway tunnel is an intractable issue. Illegal drill rig working is one of the most threatening way of intrusion. Nowadays, the distributed optic fiber sensing technology promises to provide a viable means for the long distance monitoring in the complex working conditions. To tackle the difficult problem of drill rig intrusion, we use the ultra-weak fiber Bragg grating vibration sensing array to acquire the vibration signals, and propose a real-time monitoring method based on the detection of the vibration due to the running engine. The alarm strategy identifies the engine vibration according to the narrow frequency band feature of the signal. Due to the continuity of engine working and randomness of noise interferences, the statistical analysis is adopted on the identification results. The intrusion location is achieved by the proposed method. We validate the proposed monitoring method in the field trials.