Study On Multi-component Interpretation And Full Field Apparent Resistivity Definition Of Semi-airborne Transient Electromagnetic Method With Electric Dipole On The Surface

Semi-airborne transient electromagnetic method (TEM) takes the advantages of highsignal-to-noise ratio of ground TEM and high efficiency of airborne EM. However, thismethod is rarely studied in literature. Although it has been mentioned by some scholars, therehas been no systematic discussion. Considering the unique superiorities of semi-airborneTEM, in order to spread this method into production, it is necessary to further complete itstheory.In this paper, we deduce the magnetic field in frequency domain of isotropy layeredmodels with electric dipole on the ground and analyze the kernel and integral function of bothvertical and horizontal magnetic component in frequency domain. Self-adaption Simpsonmethod and linear digital filtering method are used to calculate the magnetic responses infrequency domain and time domain, respectively. Vertical magnetic component in frequencydomain and time domain on the ground of half-space, whose analytical expression havealready been known, are used to test the accuracy of self-adaption Simpson method and250sine transform linear digital filtering method. We analyze the change of both vertical andhorizontal magnetic component in frequency and time domain of semi-airborne TEM withdifferent flight heights and offsets. Four isotropy three layered models are used to comparethe vertical and horizontal magnetic component in frequency and time domain ofsemi-airborne TEM with those of half-space. And we summarize the typical form of magneticcomponent in both frequency and time domain of different isotropy three layered models.In practice, as being restricted by the technique of instrument manufacturing, most of theinstruments collect late-time signals. Thus, it carries importance for multi-componentinterpretation. It can help us have an integral knowledge of collected signals. We find thatwhen the offset is not too large, the magnetic responses in time domain of semi-airborneTEM with electric dipole on the ground have similarities with the vertical one of groundTEM. Therefore, we consider using the polynomials of ground TEM to express those ofsemi-airborne TEM with electric dipole on the ground. At late-time, in order to simplify theform of apparent resistivity, we assume that there exists a constraint condition among theundetermined coefficients and establish the relationship between the undetermined coefficients and time variable. Then there is a series of coefficients corresponding to anypoint in the air. One half-space model, two two layered models and four three layered modelsare used to test the effectiveness of this method. Although the multi-component interpretationmethod can tell the resistivity of the last layer, it cannot reflect the electric information ofearly time and transitional period. We hope to obtain the full field apparent resistivity.Newton iteration is adopted to get the full field apparent resistivity of semi-airborne TEMwith electric dipole on the ground. One half-space model and two three layered models areused to test the effectiveness of this method. All these work in this paper will help push thesemi-airborne TEM with electric dipole on the ground into production.