Research On Interrogation Approaches Of BOTDA And FBG Co-sensing System

Accuracy is a very important issue of BOTDA sensor.This report presents a combined system of a distributed BOTDA sensor with highly accurate FBG sensors,which takes the comprehensive advantages of distributed monitoring and high resolution at specific points.Aming at one light source,multiplexing and low cost interrogation,sensor parameters of the BOTDA-FBG system are thoroughly discussed.The major work and results of this report are as follows:Based on the simulation of the Brillouin gain spectrum of a BOTDA sensing system and temperature and strain properties,we take FBGs as inserted devices of BOTDA system and focus on analysis of signal features and parameters,like spatial resolution,temperature and strain accuracy and so on.In order to enhance sensing performance,improve multiplexing ability and reduce system cost,the demodulation and multiplexing techniques of both BOTDA and multi-FBGs sensing systems are explored in this report.Based on the single sideband BOTDA system,two-dimensional edge detection algorithms(TEDAs)for vibrational location is theoretically explained and experimentally demonstrated.A signal to noise ratio(SNR)improvement of 10 dB has been demonstrated using TEDAs.The multi-longitudinal modes of the F-P laser diode together with 4 broad bandwidth FBGs is proposed to achieve FBG multiplexing and the temperature resolution based on our proposed schema reaches sensing accuracy of 0.02~oC.The system dynamic range has been also succesively extended using multiple cascaded FBGs with appropriate central wavelengths.After bring the proposed FBG multiplexing and demodulation technology into a BOTDA sensing system,a co-sensing model of BOTDA-FBG system is established.The FBGs in the co-sensing system benefit from the idle ASE gain spectrum of the BOTDA system as the light source and realize the temperature and strain accuracy of8.7~oC and 22??respectively of the BOTDA system,and 0.3~oC and 3??of FBGs.The performance parameters before and after the insertion of FBG in 1 km and 25 km BOTDA systems are compared experimentally.It is proved that BOTDA and FBG can fully play their respective advantages and complement each other in the co-sensing system under suitable wavelength,demodulation method and parameter configuration.In this report,the working mechanism and possible influencing factors of BOTDA and FBG co-sensing system are discussed theoretically.The co-sensor function of distributed BOTDA and key point FBG is realized by experiments,which provides a representative reference for a wider range of engineering applications.