Fig. 1. Schematic diagram of distributed optical fiber vibration monitoring system based on phase-sensitive optical time-domain reflection (φ-OTDR)

Fig. 2. Disturbance trace diagram of distributed optical fiber vibration monitoring system based on φ-OTDR

Fig. 3. Diagram of GAF image encoding process for manual excavation vibration signal

Fig. 4. GAF simulation of sinusoidal signal with different frequencies

Fig. 5. Flow chart of the algorithm

Fig. 6. Time-domain signal waveforms and corresponding GAF images of the six types of events. (a)‒(b) Manual excavation event; (c)‒(d) walking event; (e)‒(f) machine damage event; (g)‒(h) noise event; (i)‒(j) water flow vibration event; (k)‒(l) vehicle vibration event

Fig. 7. Accuracy curves and Loss function of GoogLeNet, VGG, and AlexNet models in training and test datastes. (a) Training accuracy of the models; (b) training Loss function of the models; (c) test accuracy of the models; (d) test Loss function of the models

Fig. 8. VGG ROC curve

Fig. 9. VGG confusion matrix

Fig. 10. AlexNet ROC curve

Fig. 11. AlexNet confusion matrix

Fig. 12. GoogLeNet ROC curve

Fig. 13. GoogLeNet confusion matrix

Fig. 14. Confusion matrices under different signal-noise ratio values. (a) Signal-noise ratio is 2 dB; (b) signal-noise ratio is 4 dB; (c) signal-noise ratio is 6 dB; (d) signal-noise ratio is 8 dB