Fig. 1. Structure of long-distance optical fiber pre-warning system

Fig. 2. Φ-OTDR vibration signal acquisition system

Fig. 3. Vibration event classification process

Fig. 4. Structure of the improved neural network

Fig. 5. Multi-scale decomposition tree of wavelet packet decomposition

Fig. 6. ANN network used for classification

Fig. 7. DNN network used for classification

Fig. 8. Three signal samples in Baoshan area of Shanghai. (a) NI event; (b) MG event; (c) ME event

Fig. 9. Comparison of signal samples before and after Max Abs Scaler. (a1)(a2) NI event; (b1)(b2) MG event; (c1)(c2) ME event

Fig. 10. Signal and its WPE distributions. (a)NI event; (b)MG event; (c) ME event

Fig. 11. Relationship between number of epoch and validation accuracy, training loss during training. (a) Validation accuracy; (b) training loss

Fig. 12. Comparison of occurrence probability of MD event in model recognition. (a) Before using the improved neural network; (b) after using the improved neural network