| Distributed optical fiber sensing technology has the advantages of distributed, high pressure and corrosion resistance, high precision, also can obtain the continuous information on distribution of measured field along the optical fiber in time and space. With the development of distributed optical fiber sensing technology, the requirement of sensing parameters is also increasing. The thesis is on the research of coherent Optical Time Domain Reflectometer(COTDR) based on the Rayleigh scattering. In the measurement of temperature and strain, COTDR has higher resolution than the sensors based on Brillouin scattering and Raman scattering, and has become a hot research topic in the field of distributed fiber sensing.In this paper, theoretical analysis and simulation of coherent Optical Time Domain Reflector are studied,and the temperature sensing experiments are carried out by using dynamic measurement method. After simulating and analyzing the COTDR dynamic temperature measurement by using MATLAB software, the COTDR system is set up and the temperature sensing experiments is studied.Respectively,7m spatial resolution, 0.1? temperature measurement at the end of 4.5km fiber and 10m spatial resolution,0.1? temperature measurement at the end of 25km fiber are realized. The experimental results show that the coherent Optical Time Domain Reflector has a very high resolution in temperature measurement. Then signal processing to the measured signal denoising is studied.The correlation of the signals is improved by averaging method and wavelet threshold denoising.COTDR system is based on the linear relationship between frequency shift and temperature to achieve quantitative detection of temperature.COTDR system is very sensitive to external environmental interference, very little noise after a long time will also lead the signals to lose relevance. There is much work to do to improve the relevance of COTDR by signal processing. |
PDF Full Text Request