Microseismic Source Location Method Based On Time Delay Estimation

Microseismic monitoring technology as a real-time,advanced and efficient means of monitoring the impact of rock pressure,widely used in coal mining,geotechnical engineering and other fields.The primary task of microseismic monitoring is to accurately and timely locate the specific location of the microseismic source.Increasing the speed and accuracy of microseismic source location is an urgent problem to be solved.There are two difficulties in the microseismic positioning process.One is the pick-up error of the microseismic signal.Due to the interference of the external environmental noise,the micro-seismic signal picked up by the sensor has an error at the time of arrival;the other is that the wave velocity model is not easy to solve.In the process of micro-earthquake inversion,the propagation speed of the signal needs to be used.However,due to the unknown internal environment of the rock mass,the velocity of the signal wave is complex and varied when it propagates inside the rock formation,which leads to errors in the inversion process of the source.Aiming at the above two problems,this paper proposes a method for locating the microseismic source based on time difference estimation.First,the microseismic signal is denoised,and then the time difference of the signal is estimated.Finally,the simplex algorithm is used to accurately locate the source.The details are as follows:(1)Because the microseismic signal collected by the microseismic monitoring system in the actual project contains a large number of external disturbances,this paper uses the improved EMD algorithm to de-noise the microseismic signal.An EMD decomposition of the noisy microseismic signal yields a series of intrinsic modal functions(IMFs)arranged in descending order of frequency.The Pearson correlation coefficient is introduced to identify the boundary between the noise component and the signal component.Perform reconstruction to achieve noise reduction of microseismic signals.(2)In order to obtain the exact time of the signal,this paper uses the generalized weighted cross-correlation time difference estimation algorithm to calculate the time difference between two signals,instead of the traditional signal pick-up,and obtains the accurate time difference between signals.After the signal is de-noised by the EMD,most of the random non-stationary noise is filtered out.The estimation of the generalized cross-correlation by the EMD de-noised signal can further reduce the residual noise interference and improve the accuracy of the time difference estimation.Through simulation experiments,the commonly used weighting functions are compared and analyzed,and the PHAT function with high estimation accuracy and good antinoise effect is selected as the weight of time difference estimation.(3)Aiming at the problem of insufficient positioning accuracy for microseismic sources,a microseism source localization algorithm based on time difference estimation and simplex method is proposed.First,the approximate position of the microseismic source is calculated by the linear positioning method.Then the spatial coordinates of the source location are taken as a vertex of the simplex.The simplex is constructed by taking the distance from this vertex to the first triggered sensor as the side length of the simplex.The objective function is constructed by using the time difference estimate and the spatial coordinates of each sensor,and the simplex method is used to find the optimal location of the microseismic source.The precise location of the microseismic source is achievedSimulation and experimental results show that the proposed algorithm can effectively filter the noise of microseismic signals under low signal-to-noise ratio,improve the accuracy of time-difference estimation,and improve the positioning accuracy of microseismic sources.