The Study About1D Forward And Inversion Of Large Loop TEM

Transient Electromagnetic Method is also known as Time Domain Electromagnetic Method. It’s a kind of electromagnetic detection method of artificial source that based on the principle of electromagnetic induction. There are many kinds of device for data collection, such as central loop, overlapping loops, large loop source, the same point dipole and dipole-dipole and so on. Among them, the large loop source is widely used, because it is the most efficient one.Departure from the basic Maxwell’s equation, this paper deduced the forward calculation formula of the large loop source TEM response inside or outside the source loops that under homogeneous half-space mode and layer earth mode. In order to calculate the double Bessel integral, this paper used the Quadrature With Extrapolation method, and compared it with tradition Numerical filtering method. And then, this paper analyzed the impact of TEM response in different modeling parameters and observation parameters. Because of the ignorance of the displacement current, oscillations will be occurred in the high-frequency part of the TEM response. And the TEM is not sensitive enough for the high-resistivity layer. Taking the central loop response as an example, this article analyzed the characteristics about normalized curve of magnetic field and magnetic field rate of changes.This paper has done some research about the TEM data inversion. The smoke loop inversion is an approximate inversion method, which is easy to realize and need not to set initial model. But the result can’t provide information about the layer thickness. So, this paper chooses LMF method, and takes inversions of several typical models. By introduction iterative control bound and measure factor of damping factor, the algorithm realized automatic adjustment of the damping factor, and enhanced stability and speed of the iterative. There are35figures,6tables, and40references in this paper.