An Application Of Distributed Optical Fiber Sensing System In Line Protection Field

The traditional monitoring technology of oil and gas pipelines has the disadvantages of high cost,susceptibility to the environment,short detection distance,and inability to achieve long-distance distributed monitoring.Optical fiber sensors have wide application prospects in the fields of security,military,pipeline protection,etc.because of their advantages of anti-electromagnetic interference,resistance to harsh environments,and so on.Among them,the distributed optical fiber vibration sensing system based on the principle of phase-sensitive optical time domain reflectometer(Φ-OTDR)has the advantages of simple structure,high positioning accuracy,and a single distributed sensing system can monitor the distance of tens to hundreds of kilometers which has attracted great attention in the field of line protection such as oil and gas pipelines and transmission lines.This paper conducts theoretical and experimental research on the problems of disturbance positioning and disturbance event classification and recognition of the Φ-OTDR distributed optical fiber vibration sensing system in the field of oil and gas pipeline monitoring.The main work completed in this article is as follows:(1)Introducing the basic principle of Φ-OTDR and the optical system structure and demodulation algorithm of the distributed optical fiber sensing system based on 3ⅹ3 demodulation technology,designing experiments to verify that the distributed optical fiber sensing system with linear amplitude response and frequency response can achieved undistorted measurement of vibration signal and using the wavelet threshold denoising algorithm and the sliding average algorithm to realize the denoising of vibration signal and improve the SNR of the system.(2)Proposing an automatic positioning method of vibration signals to achieve high resolution automatic positioning,which lays a foundation for automatic positioning and early warning of intrusion signals.Realizing locating the breakpoint of buried optical fiber by using distributed optical fiber vibration sensing system.(3)Collecting four kinds of disturbance signal,including shoveling soil,digging soil,car passing and the noise signal on the spot next to the oil and gas pipelines.Then extracting the features of the wavelet packet energy band respectively features,duration,frequency characteristic and the envelope curve’s variance from the four types of signals,combining composite feature vector with the features and using support vector machine(SVM)algorithm to realize 98.13% correct classification identification rate of the four types of signal.(4)Implementing distributed optical fiber vibration sensing system software,designing signal processing flow for signal feature extraction and classification recognition,and designing human-computer interaction interface.This paper verifies the accuracy of the sensor signal of the distributed optical fiber sensor system;performs a series of noise reduction processing on the signal,proposes an automatic intrusion signal positioning algorithm for the application of intrusion signal warning near the oil and gas pipeline and uses the SVM multi-classifier to realize the identification and early warning of intrusion signals,complete the development of early warning software and interface design which promotes the application process of distributed optical fiber sensing system in early warning of oil and gas pipelines.