Research On Distributed Optical Fiber Sensing Disturbance Pre-warning Technology Based On ?-OTDR

Based on the optical fiber's characteristics of both sensing and transmission for physical signal,distributed optical fiber sensing system can realize long-distance and continuous detection of disturbance along the sensing fiber link,which has a great promise in application of the perimeter security,electric power grid and oil or gas pipeline monitoring,and structural health diagnosis for large infrastructure.Distributed optical fiber sensing system based on different sensing mechanisms has obvious differences in measurement range,resolution,sensitivity,frequency response and so on.The distributed optical fiber sensing technology based on phase-sensitive optical time domain reflectometry(?-OTDR)has aroused wide interest of scholars at home and abroad,because of its significant advantages,including compact structure,simple signal processing,high spatial resolution and simultaneous position detection for multi-point vibration events,etc.Nowadays,traditional optical fiber pre-warning systems can only locate disturbance event or have low recognition rate.Also,the platform architecture of pre-warning system has a low degree of integration.Consequently,we aim at developing pattern classification for pre-warning system based on ?-OTDR and designing the hardware and software platform of the system.The main research contents of this thesis are as follows:(1)The basic sensing principle and research status at home and abroad of three main distributed optical fiber sensing technology of pre-warning system are reviewed,and their technical characteristics are analyzed respectively.From the introduction of generation mechanism of Rayleigh backscattering light in optical fiber,the basic structure and working principle of ?-OTDR technology are explained through establishing the mathematical model.In addition,the basic principle of pattern classification,including feature extraction and classifier design are introduced.(2)The experimental pre-warning system based on ?-OTDR is set up in the laboratory,whose sensing fiber cable is disturbed by three kinds of vibration events.The moving average and differential method are used to denoise Rayleigh backscattering signal and location respectively.Because disturbance signal is nonlinear and non-stationary,time-frequency feature of time domain signal can be extracted.Moreover,compared with time-frequency analysis method,the linear discrimination analysis is proposed to extract the feature vector of disturbance signal.Considering the disturbance classification in optical fiber pre-warning system is a nonlinear and small sample problem,we use K-nearest neighbor classification algorithm to classify and identify three kinds of disturbance events,and the recognition rate can reach 93.3%?95.6% and 88.9% respectively.(3)The distributed optical fiber disturbance pre-warning system platform based on ?-OTDR is built in this paper.We analyze the whole framework and working flow of the system and discuss the design of hardware unit.The host computer monitoring software including hardware driver and parameter configuration program,human-machine interaction display program,data processing and pattern recognition program are compiled.Finally,the disturbance experiment is tested by the designed system platform.