Quasi-Distributed Vibration Sensing Based on Weak Reflectors and STFT Demodulation

In this work, a new system is proposed for quasi-distributed vibration sensing based on the Doppler effect. The setup employs an optical frequency domain reflectometer (OFDR) and an array of weak reflectors. The short-time Fourier transform (STFT) is employed to obtain the spectrogram, then the demodulation process detects the frequency variation and compensates the accumulated response. In this manner, events occurring in the fiber segment between neighboring reflectors can be measured. The theoretical development of the approach is presented and demonstrated, evidencing the velocimeter operation of the technique. The setup has been proved in several tests under different perturbation conditions, evaluating the limitations and capabilities. This solution presents many advantages such as the ability to measure arbitrary perturbations, the linear response, high spatial-resolution, simplicity, high configurability or the low repetition rate required to detect kilohertz-frequency vibrations.