Fig. 1. Diagram of optical fiber deformation caused by external vibration

Fig. 2. Improved C-OTDR structure

Fig. 3. Waveforms of intermediate frequency signals in P state and S state

Fig. 4. Process flow of optimal selection algorithm of polarization diversity amplitude

Fig. 5. Loss test results of 2¹⁶ curves under different polarization states. (a) P state; (b) S state; (c) two states accumulation

Fig. 6. Partial enlargement of Fig. 5. (a) P state; (b) S state; (c) two states accumulation

Fig. 7. Signal amplitude waterfall near PZT in P polarization state

Fig. 8. Phase information extracted from two polarization states and reconstruction results after optimization. (a) Phase extraction result of P polarization state; (b) phase extraction result of S polarization state; (c) amplitude sum before and after perturbation position; (d) optimal result; (e) reconstructed signal after processing by optimal selection algorithm of polarization diversity amplitude

Fig. 9. Temporal and spatial amplitude waterfall diagram of water pump spraying process

Fig. 10. Vibration waveform of water impacting optical cable

Fig. 11. Temporal and spatial amplitude waterfall diagram obtained from anchor damage simulation test

Fig. 12. Time domain waveform of vibration signal measured by anchor damage simulation

Fig. 13. Schematic of two-terminal cooperation of marine cable monitoring system

Table 1. Performance comparison of long distance C-OTDR and Φ-OTDR sensing systems