Discrimination Of Temperature And Strain For BOTDR And Its Application On The Leakage Detection Of Oil Pipeline

Brillouin optical time-domain reflectometry(BOTDR)is a distributed optical fiber sensing technique.It can measure temperatures and strains at any position of fiber,and can be used in the health monitoring of optical communication cables,oil,gaspipeline,buildings,roads,tunnels,bridges and so on.Thus BOTDR has wide application prospective and has attracted much attention.BOTDR can realize the measurement by using only one end of fiber.It has advantages such as long sensing distance,easy to be connected and so on.Temperature measurement is one of the important function of BOTDR.Compared with Raman optical time-domain reflectometry(ROTDR),BOTDR has longer sensing distance and higher accuracy.Since the temperature around a leaking oil pipeline will be changed,BOTDR has good potential in the leakage monitoring of oil pipeline.However,the measurement of temperature and strain by BOTDR is mainly based on the linearly relationships of the Brillouin frequency shift(BFS)with the temperature and strain of fiber.Due to the cross sensitive of temperature and strain,BOTDR cannot discriminate the changes of temperature and strain directly using only the BFS curve,which is a severe restriction to the application of BOTDR.Thus,it’s necessary to research on the discrimination of temperature and strain for BOTDR.Meanwhile,it’s also necessary to research on the feasibility of monitoring the leakage of oil pipeline with BOTDR.This thesis introduces two researches are developed in this thesis1.Research on the discrimination of temperature and strain of fiber for BOTDR.In this method,pre-discrimination is carried out at first by using the double-parameter discrimination technique.Then the zones having temperature variation and strain variation are separated.Finally,the corresponding temperature and strain of the separated zones are recalculated by using the BFS curve.Compared with the former methods proposed in other researches,this method has advantages of better practicability and higher accuracy.2.Research on the feasibility of monitoring the leakage of oil pipeline by using BOTDR.The scheme of monitoring the leakage of oil pipeline is proposed.Then laboratory experiments are carried out to demonstrate the effectiveness of BOTDR in the leakage monitoring.Several sensing cables with different structures are evaluated in the experiments by comparing their effectiveness in the leakage monitoring and four kinds of laying styles of the sensing cables are compared as well.After that,field tests are carried out by simulating the leakage of oil pipeline and the feasibility of monitoring the leakage of oil pipeline by using BOTDR is verified.