| Fiber optic distributed sensors based on Brillouin Optical Time Domain Reflector(BOTDR) can measure the continuous parameters in space and time domain with themerits of high spatial precision, high temperature resolution, and long measuring range.The paper performs researches on demodulation techniques based on distributed fibersensor of BOTDR. The energy of different frequency signal isotained by the sweepingfrequency. In this system, envelope extraction method and its influence on the brillouinscattering spectrum extraction is studied in detail. The brillouin scattering spectrum fittingmethod of parameter estimation is analyzed. Main research works are as follows:Firstly, the generating mechanism of brillouin scattering is introduced. Based on thebrillouin effect, we study the basic theory of temperature and strain sensing, discuss therelated testing methods, and analyse the characteristics of coherent detection signal.Secondly, considering the light path design of Brillouin scattering optical time domainreflection sensor system, the signal acquisition and pretreatment in the demodulationsystem is studied with hardware and software algorithms. To improve the SNR ofdistributed BOTDR, a novel method is analyzed and verified experimentally.Thirdly, to extract the envelope signals of different frequencies in brillouin scatteringspectrum by the frequency sweep method, the basic principle of envelope extractiontechnology is studied. The hardware and software envelope detection technology isanalyzed and verified experimentally. To extract the Brillouin scattering spectrum featurein BOTDR, a novel method is introduced. Experimental results show that this algorithmcan improve the accuracy of measurement results effectively.Finally, based on the Brillouin optical time domain reflection distributed optical fibersensing system and the signal demodulation method, the distributed temperaturemeasurement is analyzed. The temperature and space resolution is obtained. |
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