[1] Li G, Zeng K H, Zhou B et al. Vibration monitoring for the West-East Gas Pipeline Project of China by phase optical time domain reflectometry (phase-OTDR)[J]. Instrumentation Science & Technology, 49, 65-80(2021).

[2] Shi Y, Feng H, Zeng Z M. Research progress of distributed optical fiber sensors based on Φ-OTDR structure[J]. Process Automation Instrumentation, 38, 70-74, 79(2017).

[3] Zhu T, Xiao X H, He Q et al. Enhancement of SNR and spatial resolution in Φ-OTDR system by using two-dimensional edge detection method[J]. Journal of Lightwave Technology, 31, 2851-2856(2013).

[4] Shi Y, Feng H, An Y et al. Research on wavelet analysis for pipeline pre-warning system based on phase-sensitive optical time domain reflectometry[C]∥2014 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, July 8-11, 2014, Besacon, France., 1177-1182(2014).

[5] Ölçer Ī, Öncü A. Adaptive temporal matched filtering for noise suppression in fiber optic distributed acoustic sensing[J]. Sensors, 17, E1288(2017).

[6] He H J, Shao L Y, Li H C et al. SNR enhancement in phase-sensitive OTDR with adaptive 2-D bilateral filtering algorithm[J]. IEEE Photonics Journal, 9, 6802610(2017).

[7] Qin Z G, Chen H, Chang J. Signal-to-noise ratio enhancement based on empirical mode decomposition in phase-sensitive optical time domain reflectometry systems[J]. Sensors, 17, E1870(2017).

[8] Zhao Z F, Liu S J, Liu D. Pipeline intrusion detection and location based on phase-sensitive optical time domain reflectometer[C]∥2018 14th IEEE International Conference on Signal Processing (ICSP), August 12-16, 2018, Beijing, China., 32-36(2018).

[9] Zhang C X, Deng Z, Wang X X et al. Application of spectral subtraction method in phase sensitive OTDR disturbance sensing system[J]. Laser Journal, 40, 16-19(2019).

[10] Cao L. Multi-scale signal processing technology in Φ-OTDR system[D]. Nanjing: Nanjing University(2019).

[11] Ibrahim A D A, Lin S T, Xiong J et al. The application of PCA on Φ-OTDR sensing system for vibration detection[C]∥2019 18th International Conference on Optical Communications and Networks (ICOCN), August 5-8, 2019, Huangshan, China., 1-3(2019).

[12] He M, Feng L, Qu J T. Denoising algorithm of Φ-OTDR signal based on clear iterative EMD interval-thresholding[J]. Optics Communications, 453, 124352(2019).

[13] Li M, Xiong X L, Zhao Y F et al. Denoising method based upon ECEMD and selective addition for Φ-OTDR[J]. Optics Communications, 452, 313-320(2019).

[14] Hu Y Z, Meng Z, Ai X B et al. Performance enhancement of the location and recognition of a Φ-OTDR system using CEEMDAN-KL and AMNBP[J]. Applied Sciences, 10, 3047(2020).

[15] He M, Feng L, Zhao D D. A method to enhance SNR based on CEEMDAN and the interval thresholding in Φ-OTDR systems[J]. Applied Physics B, 126, 1-10(2020).

[16] Dragomiretskiy K, Zosso D. Variational mode decomposition[J]. IEEE Transactions on Signal Processing, 62, 531-544(2014).

[17] Bandt C, Pompe B. Permutation entropy: a natural complexity measure for time series[J]. Physical Review Letters, 88, 174102(2002).

[18] Yan R Q, Liu Y B, Gao R X. Permutation entropy: a nonlinear statistical measure for status characterization of rotary machines[J]. Mechanical Systems and Signal Processing, 29, 474-484(2012).

[19] Zheng J D, Cheng J S, Yang Y. Multi-scale permutation entropy and its applications to rolling bearing fault diagnosis[J]. Mechanical Engineering, 24, 2641-2646(2013).

[20] Huang N E, Shen Z, Long S R et al. The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis[J]. Proceedings of the Royal Society of London Series A: Mathematical, Physical and Engineering Sciences, 454, 903-995(1998).

[21] Yu M, Sun M Y, Zhang Y L et al. Phase ambiguity and unwrapping of phase-sensitive optical time-domain reflectometer[J]. Infrared and Laser Engineering, 50, 20200437(2021).

[22] Yan X H, Zhou Z L, Li Z L. Study on the noise reduction of tractor power take-off load by empirical mode decomposition soft-threshold method[J]. Journal of Xi’an Jiaotong University, 53, 67-72, 122(2019).

[23] Zhang Y L, Yu M, Chang T Y et al. Phase-sensitive optical time-domain reflectometric system pattern recognition method based on wavenet[J]. Acta Photonica Sinica, 50, 58-69(2021).