Research On Long Haul Distributed Disturbence Sensing System Based On ?-OTDR

Phase sensitive optical time domain reflectometer(?-OTDR)features the characteristics of anti-electromagnetic interference,chemical corrosion resistance,low cost,simple layout,multi-point simultaneous positioning,high positioning accuracy,high spatial resolution,etc.It finds broad applications in long-distance oil and gas pipeline safety early-warning,structure health monitoring of large-scale buildings,perimeter security of key areas and so forth.In this paper,a long-distance phase-sensitive optical time-domain reflectometry based distributed disturbance sensing system is designed,which realized 75 km single-ended passive detection via remotely pumped relay amplification.The main innovative work includes:1.A Remotely-Pumped Erbium Doped Fiber(RP-EDF)passive amplification scheme is proposed.A three-stage narrow pulse amplification model is established.The influence of fiber length and pump power on the pulse gain is investigated.The Rayleigh backscatter intensity as well as the disturbance response of the relayed region under different pump powers are tested.An optimum pump power of 110 mW is verified with the lowest signal-to-noise ratio being not less than 10 dB.The local power requirement at the relaying position using traditional EDFA is avoided.The complexity of double-ended cooperative operation using distributed Brillouin,Raman amplification is dispensed.The system achieves 75 km single end passive disturbance monitoring..2.A demodulation algorithm based on I/Q component generation is proposed to achieve phase demodulation in ?-OTDR with no need for additional optical devices,structures or heterodyne detection.The phase of Rayleigh baskscattered light field is retrieved from two adjacent time-domain intensity signals via signal processing.The influence of nonlinear distortion of intensity signals on the sensing performance is reduced,thus assuring better linearity in the detection of external disturbance.The piezoelectric transducer is used as the disturbance source to stimulate AM disturbance(peak-to-peak value 8v,carrier frequency 110 Hz,modulation frequency 5Hz,modulation depth 70%),(peak-to-peak value 5v,carrier frequency 110 Hz,modulation frequency 20 Hz,modulation depth 80%)and FM disturbance(peak-to-peak 3v,frequency modulation range 50~200Hz,frequency modulation period 100ms),with phase demodulated in each case.3.A disturbance localization algorithm based on spatial-frequency energy spectrum is proposed.The joint energy distribution of ?-OTDR sensing signal in both spatial and frequency domain is investigated to improve the reliability of disturbance detection.It effectively reduces the influence of trace fluctuation caused by temperature variation,strain instability,laser frequency drift and so forth.The locating performance is accordingly improved.The characterization of single-frequency disturbance,broadband disturbance and coupling disturbance in the spatial-frequency spectrum is investigated,and a spatial resolution of 2m is realized at 50MS/s sampling rate.4.A parallel processing scheme of ?-OTDR sensing signal is proposed.Based on CUDA programing platform,the concurrent processing of disturbance sensing signals at each position in the sensing range is realized.The performance of parallel processing in typical ?-OTDR signal processing tasks such as moving average,batch FFT transform,and batch correlation dimension calculation was tested.Compared to serial processing,parallel processing only cosumes 1/16 computation time.