Frequency-compensation ?-OTDR Based On Image Matching

With the rapid increase of the scale of national infrastructure construction,people are increasingly demanding high-sensitivity structural health monitoring for railway tunnels,airports and ports,bridges and water conservancy and other large infrastructure facilities.Phase-sensitive Optical Time Domain Reflectometer(?-OTDR),as a highly sensitive distributed sensing technology,has been widely concerned by scholars,and has extremely important research significance and application prospects.In this paper,a frequency compensation technology based on image matching method is proposed,and the following research contents are carried out:Firstly,according to the theoretical model of the technology,the sensing mechanism of the technology based on frequency compensation principle is analyzed in detail.The sensing principles of dual-frequency ?-OTDR and sweep-frequency ?-OTDR are introduced respectively,and the feasibility of the frequency compensation technology based on image matching method is verified.Through theoretical research,the "local phase effect" of technology is also proposed.It is found for the first time that this effect will affect the linear relationship between the phase of Rayleigh scattering light field and temperature/strain.Then,this paper carries out simulation and experimental research of dual-frequency ?-OTDR based on image matching method.Through simulation analysis,it is found that the time resolution and sensing accuracy of dual-frequency technology can be significantly improved compared with the one-dimensional data matching process after the introduction of image matching method for data processing.The result of temperature sensing experiment also shows that the time resolution is improved more than four times and the sensing precision is improved nearly five times by introducing image matching method.The temperature sensitivity can reach 6 mK.In order to reduce the impact of image matching on the spatial resolution of the system,this paper uses "threshold discriminant method" to realize a distributed temperature sensor with 2 m spatial resolution.Finally,this paper carries out the simulation and experimental research of frequency sweeping technology based on image matching method.The simulation results show that the anti-noise ability of the system is improved obviously by using image matching method for data processing,which is more suitable for low signal-to-noise ratio.The results of distributed temperature sensing experiments show that the sensing accuracy of frequency sweeping technology can be improved by about 3 times and the spatial resolution can be maintained at the level of 2 m by using image matching method.In addition,the results of vibration experiments show that the frequency-sweeping ?-OTDR based on image matching method has the ability to measure dynamic microstrain,and the minimum measurable strain can reach 50 n?.