Fig. 1. φ-OTDR structure based on quasi-orthogonal chirped pulse

Fig. 2. Diagram of auto-correlation of chirped signal in matched filtering and cross-correlation of chirped signal in unmatched filtering

Fig. 3. Relationship between frequency band overlap rate and the peak of the cross-correlation

Fig. 4. The relationship between the peak of the cross-correlation and bandwidth and the overall cross-correlation value

Fig. 5. Amplitude curve of Rayleigh scattering signal

Fig. 6. Probability density distribution of the amplitude curve

Fig. 7. Intensity curve and phase trace diagram

Fig. 8. Reconstructed time-frequency information of vibration signal