基于变分模态分解的相位敏感光时域反射计信噪比提升方法  

Enhancement of Signal-to-Noise Ratio Based on Variational Mode Decomposition for Phase-Sensitive Optical Time Domain Reflectometry

作　　者：高浩天 康杰虎 张振 吴斌[1] Gao Haotian;Kang Jiehu;Zhang Zhen;Wu Bin(National Key Laboratory of Precision Testing Techniques and Instrument,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学精密测试技术及仪器国家重点实验室,天津300072

出　　处：《光学学报》2023年第21期41-50,共10页Acta Optica Sinica

基　　金：四川省科技支撑计划(2021YFSY0024)。

摘　　要：在页岩气开采过程中,基于相位敏感光时域反射计(Φ-OTDR)的分布式光纤声波传感(DAS)系统是对水力压裂作业中产生的微震波进行监测的常用方案。为了提高Φ-OTDR系统测量振动信号的信噪比,提出了一种基于变分模态分解(VMD)和互信息(MI)的振动信号去噪方法,对数字正交(I/Q)解调得到的相位信号进行进一步处理,VMD层数K通过去趋势波动分析(DFA)计算的标度指数确定,相位信号的失真和噪声通过剔除MI法确定的非相关模态进行抑制。并搭建了相干探测Φ-OTDR系统验证VMD-MI方法的去噪效果,分别对500 Hz单频振动信号和500、1000、1500 Hz多频振动信号使用VMD、小波降噪(Wavelet)、经验模态分解(EMD)、自适应噪声完备集合经验模态分解(CEEMDAN)进行处理。实验结果表明,所提方法对振动信号信噪比提升最为明显,在Φ-OTDR系统中具有良好的实用性。Objective During shale gas exploitation,a distributed optical fiber acoustic sensing system(DAS)based on phasesensitive optical time domain reflectometry(Φ-OTDR)is a commonly employed solution for monitoring microseismic waves generated during hydraulic fracturing operations.Signal-to-noise ratio(SNR)is an important parameter reflecting the performance of theΦ-OTDR system,and obtaining microseismic signals with good SNR is the basis for monitoring the fracturing effect of shale gas.However,due to the thermal noise and scattering noise of the photodetector,the phase noise and frequency drift of the laser,and the environmental noise,the SNR of theΦ-OTDR system will deteriorate,resulting in difficult vibration localization and distorted phase signal obtained by demodulation.The solution to this problem is essential for broad applications ofΦ-OTDR systems in the engineering field.Methods To improve the SNR of vibration signals measured byΦ-OTDR systems,we propose a vibration signal denoising method based on variational mode decomposition(VMD)and mutual information(MI).The in-phase orthogonality(I/Q)demodulated phase signal is further processed,and the number of VMD layers K is determined by the scaling index calculated by detrended fluctuation analysis(DFA).The process of the DFA method is as follows.First,the input noisy signal is decomposed into K(K=1,2,3…)IMF components by VMD,and then the scaling index of each mode is estimated by DFA.The relationship between the number of decomposition layers K and the scaling index is K=arg mKax[num(α1:K≥θ)=J,K=1,2,3,⋯],where the parameter J is determined by the scaling index of the input noisy signal.When the value of K is determined,the MI between the IMF components generated by the K-layer VMD and the input noisy signal is calculated.The mean value of the normalized MI of each component and the input signal is taken as the threshold value.Additionally,when the normalized MI of a component and the input signal is greater than this threshold value,the component is

关 键 词：相位敏感光时域反射计 水力压裂微地震监测 信噪比 变分模态分解 互信息 

分 类 号：TP212[自动化与计算机技术—检测技术与自动化装置]