Distributed Optical Fiber Perimeter Security Technology Based on Φ-OTDR with Interference Fading Suppression
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摘要:
基于相位敏感光时域反射计（Φ-OTDR）的分布式光纤振动传感系统在铁路周界安防中有着重要的应用前景. 为降低Φ-OTDR中固有的相干衰落对相位解调的影响，提高扰动信号识别率，提出一种基于矢量旋转滑动平均（MVRA）的相干衰落抑制方法. 首先，对探测信号复矢量化，并对各位置的复矢量信号按初相角进行旋转对齐；然后，采用滑动平均的方法缓和信号幅度起伏以及减小噪声功率，提高信噪比，进而抑制相干衰落；其次，从衰落抑制信号解调出扰动信号，将MVRA与频谱提取重组（SERM）、数字向移变换（DPST）方法进行对比，通过差分相位标准差验证抗衰落效果；最后，通过搭建分布式光纤周界入侵检测实验平台，模拟环境噪声、应力破坏、攀爬、剪网4种防护扰动信号，以解调的相位灰度图作为特征图像，使用卷积神经网络进行模式识别. 实验结果表明：相比SERM、DPST，MVRA能更高效地抑制衰落，当滑动窗长50 ns时，MVRA提高11.2 dB信噪比；扰动信号的识别率由衰落抑制前的88%提高到衰落抑制后的92%.
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关键词:
- 相位敏感光时域反射计 /
- 相干衰落 /
- 周界安防
Abstract:Distributed optical fiber vibration sensor based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) has important application prospects in railway perimeter security. In order to reduce the influence of inherent interference fading in Φ-OTDR on phase demodulation and improve the recognition rate of disturbance signals, an interference fading suppression method based on moving vector rotating average (MVRA) was proposed. Firstly, the detected signal was characterized by a complex vector, and the complex vector signals at each position were rotated and aligned according to their initial phase angles. Then, the moving average method was used to improve the signal-to-noise ratio by mitigating the fluctuation of the signal amplitude and reducing the power of the detected noise, thereby suppressing interference fading. Next, the disturbance signal was demodulated from the suppressed fading signal. MVRA was compared with spectrum extraction and remix (SERM) and digital phase-shift transform (DPST) methods, and the anti-fading effect was verified by the standard deviation of the differential phase. Finally, an experimental platform for distributed optical fiber perimeter intrusion detection was built to simulate four kinds of protective disturbance signals, including environmental noise, stress damage, climbing, and net shearing. The demodulated phase grayscale image was taken as the feature image, and then a convolutional neural network was used for pattern recognition. The experimental results show that MVRA can suppress fading more efficiently than SERM and DPST. When the sliding window length is 50 ns, the signal-to-noise ratio is improved by 11.2 dB, and the recognition rate of disturbance signals is increased from 88% before fading suppression to 92% after fading suppression.
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图 2 外差相干探测 Ф-OTDR实验装置
Figure 2. Experimental setup based on Ф-OTDR for heterodyne interference detection
图 3 原始探测信号解调的幅度和差分相位
Figure 3. Demodulated amplitude and differential phase of original detected signal
图 4 衰落抑制后信号的解调的幅度和差分相位
Figure 4. Demodulated amplitude and differential phase of signal after fading suppression
图 7 功率谱密度在频率10 kHz处沿距离轴的分布
Figure 7. Distribution of power spectral density along distance axis at frequency of 10 kHz
图 8 SERM、DPST和MVRA衰落抑制后解调的差分相位标准差
Figure 8. Standard deviation of demodulated differential phase after fading suppression by SERM, DPST, and MVRA
图 9 周界入侵监测实验平台及防护网
Figure 9. Perimeter intrusion monitoring experimental platform and protective net
图 10 衰落抑制前后4种模拟扰动的模式识别结果
Figure 10. Pattern recognition results of four simulated disturbances before and after fading suppression
表 1 相干衰落抑制前后4种振动模式下解调的差分相位
Table 1. Demodulated differential phase under four vibration modes before and after interference fading suppression
模式 890 m 处解调的相位信号 原始信号解调的相位
分布局部截图衰落抑制后解调的相位
分布局部截图风吹信号 
晃动信号 
敲击信号 
剪切信号 
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