Fig. 1. Ф-OTDR sensing principle diagram

Fig. 2. Schematic diagram of differential-compensation-accumulation demodulation algorithm

Fig. 3. Φ-OTDR experimental setup diagram

Fig. 4. Amplitude demodulation and location results. (a) 200 amplitude curves; (b) moving differential positioning curve

Fig. 5. Comparison of 60 Hz external vibration unfolding phase backward differential processing. (a) Unwrapped phase without backward differential; (b) backward differential unwrapped phase

Fig. 6. Time-domain demodulation result of differential domain compensation phase for 60 Hz external vibration. (a) 1000 ms; (b) 100 ms

Fig. 7. Demodulation phase results of differential-compensation-accumulation algorithm

Fig. 8. Phase time-domain waveforms and spectrograms of phase demodulation using differential-compensation-accumulation algorithm and traditional unwrapping algorithm. (a) Phase time-domain waveform demodulated by differential-compensation-accumulation algorithm; (b) spectrogram demodulated by differential-compensation-accumulation algorithm; (c) phase time-domainn waveform demodulated by traditional unwrapping algorithm; (d) spectrogram modulated by traditional unwrapping algorithm

Fig. 9. Phase power spectral density (PSD) diagrams for differential-compensation-accumulation algorithm and unwrapping algorithm demodulation. (a) Differential-compensation-accumulation demodulation; (b) unwrapping algorithm demodulation

Fig. 10. Time-domain results of compensated phase in differential domain for different external vibrations. (a) 5 V, 20 Hz; (b) 1.5 V, 100 Hz (Inset shows zoomed-in 100 ms time-domain plot)

Fig. 11. Demodulated phase result plots for external vibrations at frequencies of 20 Hz and 100 Hz. (a) Demodulated phase time-domain waveform of 20 Hz sinusoidal signal; (b) demodulated phase time-domain waveform of 100 Hz sinusoidal signal (Inset shows zoomed-in 100 ms time-domain plot); (c) demodulated phase PSD of 20 Hz sinusoidal signal; (d) demodulated phase PSD of 100 Hz sinusoidal signal