Research On The Suppression And Application Of Magnetotelluric Static Effect Based On Wavelet Threshold

Magnetotelluric sounding(MT)is a frequency domain sounding method that uses natural field sources to study the electrical structure inside the earth.Based on the different attenuation degrees of electromagnetic waves of different frequency in the earth medium,the magnetotelluric method can detect the resistivity of underground media information from shallow to deep.MT is widely used in energy exploration and deep mineral resources exploration due to its advantages of using natural field source,light equipment,large detection depth,wide frequency range and not being shielded by high resistance layer.However,the static effect in magnetotelluric method is objective and inevitable,which will make the inversion results produce false anomalies,increase the difficulty of subsequent data interpretation,and seriously affect the exploration results.Therefore,it is necessary to suppress the static effect.This paper proposes a static effect suppression method based on wavelet threshold.The main work is as follows:Firstly,it analyzes the mechanism and typical characteristics of the static effect based on the basic theory of electromagnetic field,discusses the influence of the buried depth,transverse width,longitudinal thickness and resistivity value of the local electric inhomogeneous body on the offset of the static effect by using the finite element two-dimensional forward modeling software to simulate different geoelectric models,researches the influencing characteristics and the identification method of static effect.Secondly,in view of the wavelet analysis theory,the paper researches the basic principle of wavelet threshold denoising in suppression static effect and improves the threshold function.Combining the filtering scalar to select a reasonable wavelet basis function and decomposition scale,calculate the threshold of each layer based on the decomposition scale,and apply the improved threshold function to the suppression of static effect.The forward model can prove the effectiveness of the improved threshold function in static effect suppression.Not only the static effect can be suppressed effectively,but the regional anomaly information can be retained well through the improved threshold method.At the same time,it processes the above models using five points,seven points,median filtering and wavelet analysis and compares the suppression effect of several filtering methods.Then,this paper constructs the static effect correction system.It distinguishes the static effect and anomalous body by correlation coefficient,uses wavelet threshold method to suppress the static effect,and embeds five points filtering,seven points filtering,median filtering and wavelet analysis to facilitate comparative analysis.Finally,apply the wavelet threshold method and static correction system to the actual data processing of Yimen copper mine in Yunnan,which effectively suppresses the static effect,improves the quality of data interpretation,and verifies the stability and reliability of the static correction system.The thesis also discusses the algorithm deficiencies of static effect suppression,and puts forward some suggestions about the further research work.