An Interrogation Method to Enhance SNR for Far-End Disturbances in Fiber-Optic Distributed Disturbance Sensor Based on $\varphi$ -OTDR

In this paper, an interrogation method for a fiber-optic distributed disturbance sensor based on φ-optical time reflectometry to enhance the signal-to-noise ratio (SNR) for far-end disturbance is proposed. The wavelet de-noising based on simulated annealing algorithm with an adaptive threshold is utilized to smooth the noises and recover the signal. Then, the 2-D edge detection is employed to detect and locate multiple disturbances, simultaneously by calculating the spatial gradient of the grey image of the Rayleigh backscattering traces. This method is validated in a long-term field test, and three different disturbance events are detected and located along a 25.05-km-long sensing fiber, simultaneously. Experimental results show that the proposed method can reduce the gain imbalance between the front end and far end due to the attenuation of Rayleigh backscattered light, which means that it is effective to improve the SNR of far-end disturbance and recognize the location of disturbance in a harsh environment with strong background noises.