Stability And Environmental Adaptability Of ?-OTDR Distributed Optical Fiber Disturbance Sensing System

?-OTDR distributed optical fiber sensing technology has been widely studied and applied because of its incomparable advantages in the long distance localization and real-time monitoring.However,with the deepening of engineering applications,a number of scientific problems in the system stability and environmental adaptability are exposed.Theory,experiment and engineering application of ?-OTDR distributed optical fiber disturbance sensing system and its strain signal acquisition,system stability,environmental adaptability are studied for application needs.Firstly,optical transfer matrix model of the ?-OTDR distributed optical fiber sensing light path is established,and the integrated backscatter signal expression and disturbance location expression are derived.Based on the model,optical backscatter traces and power cost are simulated and optimal optical parameters are obtained.There is a wavelet packet in the multi-period average track when the sensing fiber is disturbed by single point.We get the disturbance frequency response curves and find that when the disturbance frequencies lower than 50Hz the system does not work.An ?-OTDR distributed optical fiber disturbance sensing experimental system is built,and backscattering tracks,wavelet packets and frequency response are consistent with the simulation results that verify the optical transmission matrix model.Sencondly,based on Shannon's law the scheme of ?-OTDR distributed optical fiber disturbance strain acquisition is proposed,and transfer matrix model is established.Optical signal receiving and processing module and ?-OTDR distributed optical fiber disturbance strain acquisition experimental system with delay fiber 6km,sensing fibre 10km,wavelength 1310nm are developed.Experiments for acquiring different locations and frequencies disturbance strain are carried out,and signal restored consistent with the original strain signal that verify the strain signal acquisition scheme.Thirdly,engineering solutions are proposed for the loss of fiber fusion point and false alarm of harmless invasion.A lot of fiber fusion point comparative experiment are carried out,and the results show that the loss of fiber fusion points by polarization-maintaining fusion splicer is low and high stability of temperature and humidity.The scheme of disturbance pattern recognition and classification based on the threshold-crossing rate is proposed,and?-OTDR distributed optical fiber disturbance sensing engineering model system with with delay fiber 6km,sensing fibre 4km,wavelength 1310nm are developed.Experimental results show that the proposed programme filters harmless intrusions,and event recognition rate is greater than 95%.Above solutions improve application stability of ?-OTDR distributed fiber disturbance sensing system.Finally,when the sensing cable is exposed to the atmosphereare the problem of false alarm produced by raindrops is studied deeply.Analyzing raindrops and fiber interaction dynamics processes,the expression of backscatter phase variation by raindrops is derived.Parallel sensing fiber dynamic rainfall compensation scheme is proposed and the disturbance criteria are given.A dynamic rainfall-compensated ?-OTDR distributed optical fiber disturbance sensing and perimeter security system is built,and experimental results verify the dynamic rainfall compensation scheme.A simplified rainfall compensation engineering system using udometer is proposed and developed.Disturbance identification and location is realized and the system is function properly under rainfall environment.