Abstract
A pulse-width multiplexing method for reducing the nuisance-alarm rate of a phase-sensitive optical time-domain reflectometer (-OTDR) is described. In this method, light pulses of different pulse-widths are injected into the sensing fiber; the data acquired at different pulse-widths are regarded as the outputs of different sensors; and these data are then processed by a multisensor data fusion algorithm. In laboratory tests with a sensing fiber on a vibrating table, the effects of pulse-width on the signal-to-noise ratio (SNR) of the -OTDR data are observed. Furthermore, by utilizing the SNR as the feature in a feature-layer algorithm based on Dempster–Shafer evidential theory, a four-pulse-width multiplexing -OTDR system is constructed, and the nuisance-alarm rate is reduced by about 70%. These experimental results show that the proposed method has great potential for perimeter protection, since the nuisance-alarm rate is significantly reduced by using a simple configuration.
Highlights
Phase-sensitive optical time-domain reflectometry (φ-OTDR), a powerful tool for distributed intrusion sensing in perimeter protection, has attracted increasing interest since it was proposed in1993 [1]
The data from different pulse-widths were regarded as the outputs of four different sensors and were processed by a multisensor data fusion algorithm
These results indicate that the pulse-width multiplexing method is a powerful tool to eliminate false and missing alarms
Summary
Phase-sensitive optical time-domain reflectometry (φ-OTDR), a powerful tool for distributed intrusion sensing in perimeter protection, has attracted increasing interest since it was proposed in1993 [1]. In a φ-OTDR system, light pulses of a fixed width are injected into a sensing fiber, and Rayleigh-backscattered light is acquired to distinguish the intrusion event, as well as its location. The sensing range is usually of the order of tens of kilometers, so the sensing fiber cable may pass across different terrains, such as deserts, swamps, rivers and lakes, and different parts of the cable may encounter different weather conditions, such as hurricane, rain, snow and hailstorms. Because of the complications introduced by terrain, weather conditions and polarization fading, φ-OTDR suffers from a serious rate of nuisance alarms, which hinders its practical application. To decrease the nuisance-alarm rate, a variety of methods based on data processing, including algorithms for filtering, noise reduction, feature extraction and pattern recognition, for example, have been proposed. Bao and co-workers [4,5] proposed a moving-average together with moving-differential method, as well as a wavelet denoising method to reduce the average number of nuisance alarms
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