Research On Signal Enhancement And Processing Of Fiber Distributed Acoustic Sensor System

Distributed optical fiber sensing has been widely used in modern society due to its long sensing distance,many measurable parameters and high sensitivity.?-OTDR,based on the principle of Rayleigh scattering effect of the signal light in the fiberas,is a kind of distributed optical fiber sensing,it can detect tiny disturbances along the sensing optical fiber in real-time.In recent years,it has been successfully used in oil exploration,geological structure detection,pipeline safety monitoring and other fields.DAS technology,based on the basis of traditional ?-OTDR,can demodulate the phase of Rayleigh scattering signal in the optical fiber,furthermore it can real-time monitor and quantitative reduction the external disturbances,thus it becomes the most development potential of the optical fiber sensing technology.In the practical application of DAS technology,it is still faced with the challenges of short sensing distance caused by optical fiber transmission loss and low OSNR.First of all,through the design of the DAS system based on bi-directional first-order Raman amplification technology,the influence of the transmission loss along the sensing optical fiber on the signal pulse is overcome,thus the sensing distance of the system has been effectively extended: at the front end of the sensing fiber,the forward Raman pump light energy transfers to the detection signal light to provide Raman gain,realizes the amplification of signal light.Then due to the forward pump power depleted,it can no longer provide gain for signal light.When signal light transmits to 80 km of the fiber,backward Raman pump starts to provide gain for the signal light.The sensing distance of the single pulse DAS system built with the above scheme reaches 100 km,the spatial resolution is 10 m,and the strain resolution is 122 (?),which verifies the effectiveness of the scheme.In addition,due to the weak Rayleigh scattering intensity in the SMF,the detection signal of DAS system is weak.In order to solve this problem,this paper also studies the scheme to improve the sensing performance of DAS system by using the fiber with wide bandwidth UWFBGs as the sensing fiber.The backward reflected light power in the microstructure fiber with wide bandwidth UWFBGs is obviously higher than the Rayleigh scattered light power in the SMF.Therefore,using it as the sensing fiber can significantly improve the intensity of the detected signal,the signal-to-noise ratio at the receiver,and then improve the strain resolution of DAS system.Further,this paper studies the methods to suppress DAS signal noise from the perspective of digital signal processing.By comparing different signal processing methods,a zero-phase filtering scheme suitable for DAS system is proposed.Through simulation and experimental verification,it is proved that the scheme can effectively suppress the high-frequency noise of the system and solve the problem of phase distortion caused by ordinary IIR filtering.