Location Method Study For ?-OTDR Based On Ensemble Empirical Mode Decomposition And Multi-scale Wavelet Decomposition

Phase-sensitive optical time domain reflectometer(?-OTDR)optical fiber distributed sensing system is widely used in various fields for the advantage of high accuracy of location,simultaneous location of multi-point disturbance,high resolution,simple signal processing,it has gradually become a hotspot in the research of distributed fiber-optic disturbance sensor system.The nuisance alarm rates and missing alarm rates of ?-OTDR distributed fiber-optic disturbance sensor system in the complex environment are the keys to decide whether the system can be applied.In this thesis,we focus on the problems of high nuisance alarm rates and missing alarm rates generated by?-OTDR distributed fiber-optic disturbance sensor system and we carry out in-depth theoretical and experiment research.The main research work is described as follows:(1)According to the theory of optical waveguide and elasticity,the optical signal transmission mathematical model of ?-OTDR distributed optical fiber sensing system is established,and the perturbation signal is analyzed and studied,which provides a theoretical basis for the location algorithm.(2)Based on the analysis of the application background of ?-OTDR distributed optical fiber disturbance sensing system,a new location method based on ensemble empirical mode decomposition(EEMD)and multi-scale wavelet decomposition(MWD)is proposed to solve the problem of high nuisance alarm rates in engineering application.The EEMD thresholding method is used to process the time-domain signal of each sensing zone,and the multi-scale wavelet decomposition is performed on the denoised signal to separate the phase noise of the system and the external environment noise and extract the disturbance signal,so that the nuisance alarm rates and missing alarm rates of the system are reduced.(3)The ?-OTDR distributed fiber-optic disturbance sensor system is set up and the feasibility verification and the accuracy test of the proposed algorithm based on EEMD-MWD are carried out at the actual project.A single point disturbance experiment in 36th sensing zone and a multi-points disturbance experiment in 187th,339th sensing zones are carried out.According to the 165 groups of test data,the signal-noise ratio(SNR)of signal has been significantly improved,the nuisance alarm rates and missing alarm rates dropped to 2.42%,3.64%.