A novel hybrid BOTDR and Φ-OTDR system for simultaneous static and dynamic measurements is proposed. Employing the division of both backscattering light and local light, a double coherent detection configuration is achieved to extend the sensing range and demodulate the phase quantitively. With the independent detection of Brillouin scattering light and Rayleigh scattering light, the demodulation error in BOTDR is avoided while the signal-to-noise ratio of Φ-OTDR is enhanced. Experiment for simultaneously measuring temperature and vibration is carried out, which proves the sensing range of the hybrid system is 49.5km with 20m spatial resolution. The measurement uncertainty of BOTDR is verified to be 2.821MHz, and the maximum frequency response range of Φ-OTDR is 900Hz. Experimental results indicate the proposed system is specialized in dealing with both static and dynamic situations simultaneously.
Aiming at improving the signal processing capability of polarization optical time domain reflectometry (POTDR), a recognition method mainly based on the feature extraction and supported vector machine (SVM) is proposed. Apart from locating the certain place of interruptions, this method can help us identify different kinds of intrusion events. Firstly, we preprocess the signal by using an average filter and setting a proper threshold for it. Secondly, the signal is transformed into various kinds of time-domain features and frequency-domain features for the subsequent classification. Finally, the SVM of the system is trained with initial signals so it can discriminate events represented by new signal accurately. Our experiment results show the effectiveness of this method, and it can work well with high accuracy, fast response speed and low cost.
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