THEORETICAL ANALYSIS AND NUMERICAL CALCULATION OF LOOP-SOURCE TRANSIENT ELECTROMAGNETIC IMAGING
回线源瞬变电磁成像的理论分析及数值计算

In order to improve the prospecting precision to the earth of the transient electromagnetic method(TEM), the principle of TEM imaging technology and a numerical calculation method are put forward. Transient electromagnetic response to the layered earth is discussed in the frequency domain, then a double integral in which the kernel is unknown is obtained. The solution of the electromagnetic field in the medium of layered earth is separated into the forms of upper and down traveling waves. Then a set of linear equations in which reflection coefficients are unknown is reached. The numerical solution of wave-impedance and reflection coefficients is given as follows: Transforming the magnetic field data from time into frequency domain, replacing the kernel of equation with the equivalent wave-impedance of homogeneous half-space, getting the equivalent wave-impedance in the frequency domain after digital filtering, then returning the equivalent wave-impedance into the time domain, constructing equations with it, getting reflection coefficients from the equation with the method of linear programming in the time domain. The imaging result section can be drawn according to it. The imaging result from the theorical model shows that the method proposed in this paper can improve greatly the ability to recognize the underground electric interfaces.