High Efficiency Positioning of Vibration Intrusions for Long Distance Perimeter Security Monitoring Based on Time-Frequency Variation Envelopes

Monitoring long distance perimeter security using distributed optical fiber vibration sensing technology to detect potential intrusions with high efficiency is crucial for its successful application in practical engineering. In this article, an asymmetric dual Mach-Zehnder interferometer based long distance distributed optical fiber perimeter security system is constructed to accurately and rapidly locate the vibration intrusions based on an improved time-frequency variation envelope extraction scheme. First, signals received from the long distance optical fiber perimeter security system are filtered by a mean filtering method. Thus the low-frequency noises can be effectively eliminated and the starting points of the received vibration signals caused by the applied intrusions can be rapidly acquired. Second, the variation features and envelopes of the intrusion signals are extracted by a variational mode decomposition based approach, which can successfully suppress the asymmetry of the received sensing signals. Third, the time delay between the received interference signals is acquired by performing a cross-correlation method to the extracted envelopes. So the vibration position on the sensing fiber can be correctly acquired. To validate the feasibility of the proposed positioning scheme, we conduct a series of field tests by perturbing the fence on the constructed long distance optical fiber perimeter security system. The results show that the mean processing time of the proposed positioning scheme can be greatly shortened to 74 ms. Moreover, the average positioning error of 35.5 m is also realized in a sensing length of 101 km. With the significant advancements in efficiency and accuracy, we believe that the proposed scheme has great application potential in the field of long distance optical fiber perimeter security systems.