Research On Full-waveform DC Data Characterization And Noise Suppression Techniques

DC resistivity method is an important tool of geophysics,which is a method based on the difference of medium apparent resistivity for application purposes.However,in the application,the effective signal is often subject to external interference causing a decrease in the accuracy of the original data.Common external interference includes industrial frequency noise,stray current noise,Gaussian white noise,etc.,which have different degrees of impact on the inversion results of the electric method of exploration,especially on the image of the electric method of monitoring data is serious,the electric method of monitoring small-scale seepage events,weak anomalous signs,small gradients of anomalous potential changes,which are more difficult to identify in the presence of interference.Therefore,it is of great significance to further improve the quality of the exploration signal for the accuracy of environmental monitoring.Based on the theory of resistivity method orthorectification,the thesis analyzes the influence of noise on DC electrical method signal and studies the technique of noise reduction of full waveform DC electrical method data to achieve the purpose of improving the signal-to-noise ratio,as follows:(1)The DC resistivity method orthorectified model is studied.Firstly,the thesis implements the numerical simulation of DC resistivity method based on finite difference method through Matlab software,and the theoretical numerical signal of DC resistivity method is derived using symmetric quadrupole device;finally,the accuracy of the model is verified through theoretical data analysis.The influence of various interference noises on the signal is analyzed,among which the irregular random noise has the most serious influence.(2)To study the noise reduction effect of noise reduction methods on different types of noise.The combination of empirical modal decomposition(EMD),sliding average and least squares fitting denoising methods and related principles are studied for noise containing different types and intensities of noise,and are implemented by Matlab software programming.And compared with the traditional arithmetic average and wavelet denoising,the effectiveness and accuracy of this denoising method are concluded.(3)Analysis of the measured data.The reliability of the instrument used was verified by laboratory experiments.By adding the pure noise measurement of the earth without power supply to the resistance measurement signal without noise interference and denoising it using the denoising method in this paper,the values of the denoised signal and the noise-free signal were obtained to match basically.Finally,the measured DC resistivity method signal is denoised to make the coal mine safety monitoring and environmental monitoring signals more accurate and reliable.