Study on frequency domain electromagnetic sounding method based on equivalent opposing coils
The frequency domain electromagnetic sounding method in the near-field of artificial sources has advantages such as portability,high resolution,and strong anti-interference ability.However,the problem of extracting the secondary field response of geological bodies has hindered the widespread application of this method.By extracting the secondary field response based on the principle of equivalent opposing coils,this study first derives the expression of the frequency domain near-field perpendicular magnetic field response based on the principle of equivalent opposing coils;then,the ratio of the in-phase component of the vertical magnetic field of layered media to that of homogeneous half-space media is defined as the apparent resistivity and the frequency response of the vertical magnetic field for typical layered media is calculated;finally,a comparative experiment is conducted to compare the anomalous responses of the time domain and frequency domain methods to shallow-buried aluminum plates.The results show that the princi-ple of equivalent opposing coils can effectively extract the near-field frequency domain secondary field signals based on the principle of equivalent opposing coils,and the in-phase component of the near-field vertical magnetic field is directly proportional to the square of the magnetotelluric conductivity.The apparent resistivity defined by the ratio of the in-phase component of the vertical magnetic field can clearly reflect the characteristics of A-type,Q-type,H-type,and K-type geoelectric cross section.
frequency domain electromagnetic soundingequivalent opposing coilsin-phase componentnear-field surveyapparent resistivityanomalous response
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万方数据
维普
