Fig. 1. Schematic of ADMZI vibration sensing system

Fig. 2. Schematic diagram of the processing algorithm for positioning

Fig. 3. Schematic diagram of the frequency allocation process in WSST

Fig. 4. Simulation analysis of the interference signals. (a) Two-channel interference signals; (b) Power spectrum of one of the interference signals; (c), (d) Time-frequency spectra of the interference signal based on the CWT and WSST; (e) The envelopes of absolute wavelet coefficients (EAWCs) of the two interference signals based on the CWT; (f) The mean modulus of the WSST (MMW) of the two interference signals

Fig. 5. TDE errors using the CWT and WSST positioning methods when the SNR is varied from 5 dB to 45 dB

Fig. 6. Time-frequency analysis of the interference signal. (a) CWT time-frequency spectrum of the interference signal; (b) WSST time-frequency spectrum of the interference signal

Fig. 7. Signal processing of the proposed WSST positioning method. (a) Two interference signal segments extracted from the CW and CCW directions; (b) Power spectrum of one of the interference signals; (c) Phase variation characteristic curves of the two interference signals; (d) Cross-correlation waveform of the phase variation characteristic curves

Fig. 8. Positioning results on the end of the armored fiber optic cable over 128 km long sensing fiber link. (a) Positioning errors based on the proposed WSST method; (b) Comparison of the distribution of positioning results based on the CWT and WSST method