| Time-domain transient electromagnetic method (TEM) is a kind of geophysical exploration method based on electromagnetic induction detecting targets through electrical and magnetic difference of properties, which explores the underground through receiving a secondary electromagnetic field induced by transient current underground and is an indispensable method of geophysical Land and resources survey. Transient electromagnetic method has been used as conventional geophysical methods, widely used abroad for many years. In this article, mainly through one way or another to deal with transient electromagnetic data in order to obtain stratigraphic information needed.Shallow groundwater zone of TEM survey in China is mainly Quaternary sediments, and so the choice of Layered model is appropriate. But more the difficulties results than satisfactory. Because the mathematical inversion are multiple solutions, and the inverse problem function is non-linear equations. In addition, the measured data exists to zero drift and random error. If the inappropriate choice of the initial model, it may not be a reasonable solution; even if the appropriate initial model choice, practice has proved that the success or failure of the transient electromagnetic method inversion much depends on the choice of the initial value. Indeed, choose a suitable non-linear equations method is one of the keys to solve the problem, is also the key issue of the study in this article. LMF method for transient electromagnetic data interpretation described in this article reads as follows:(1),Introduced the one-dimensional theory calculation of time-domain TEM for loop source on layered earth. Including the establishment the launching-receiver model on layered underground, analysis under the model, and deriving frequency-domain electromagnetic response expressions. The expression contains a double integral, Hankel transformation can be used to solve the inner integral containing Bessel functions, we use complex integration of Simpson to solve the outer integral. Guptasarma Algorithm helps the conversion from the frequency-domain to time-domain. The correctness is proved. through the comparison with Brian and Nabighian TEM theoretical responses under the same earth model.(2),Research Newton-Gauss equation, and derived the LMF method from its evolution. In the LMF method, if the choice of damping factor is appropriate, formation parameters can have a good convergence effect, which can avoid multiple solutions and that the target error may be emanative. In order to automatically adjust the damping factor, the use of Levenberg (1944) and Marquadt (1963) method of improve the damped least square method to complete the automatic adjustment of the damping factor. The choice of the initial model determines the success or failure of inversion, Determine the upper and lower bounds of model parameters to limit the scope of the parameters modified. The feasible direction method help adjusting the model, that we can realize transient electromagnetic data interpretation with man-made debugging and computer automatic calculating.(3), We choose a typical earth model of the 2,3,4 layers as a reference and use LMF method to process theoretical TEM data as a result that Inversion results are in line with the strata parameters of the various earth model with fast convergence and small error parameters,which prove that LMF method is applicable to TEM data. The inversion results of the theoretical transient electromagnetic data with simulation error are basically in line with the formation parameters of the model, but the deep-seated parameters exist deviation, data error on the inversion results of a large extent, data error has a large effect on inversion results.(4), We studied that the LMF method inversion for the wild transient electromagnetic data in Zhengxiangbai Banner in the Inner Mongolia, and make the contrast between what we got and the original one of the apparent resistivity interpretation. Although the results are unsatisfactory, however, from 18 measurement points under 4-layer earth resistivity mapping results can be seen in the similarities between the two. The LMF method is still needed to improve its algorithm in order to be applied to the interpretation of field data. In this paper, we verified the LMF method is adequate for the one-dimensional layered earth interpretation of transient electromagnetic data.In this article, we studied the basic computer automatically processes for TEM data interpretation, data for a detailed explanation of the geological mapping laid the foundation for mapping, also laid the foundation for rising more low-rise in the next inversion of the earth model in order to draw more detailed geological mapping.
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