Fixed-loop TEM Data Processing Algorithm Research Based On SVD

Transient electromagnetic method can also be called Time-domain electromagnetic method(TEM),is a kind of geophysical exploration method based on electrical difference of properties for surveying low resistance targets and researching the earth structure of shallow and middle shallow. The most popular devices of TEM are center-loop,overlap-loop and dipole-dipole device,and the data processing softwares of these devices have been used widely.However,when we work outside using these devices,the amount of work is great for we need to move the transmitter loop again when survey another point.So more and more attention is paid to the fixed-loop devices.This paper is based on the SVD,studying the TEM data processing algorithm of fixed-loop. The main research work and achievements are as follows:1.Know deeply the work principle,equipment and instrument structure of the MRS and TEM associated instrument. Study deeply the basic theory of electromagnetic fields,as for the work equipment of the TEM mode, transient electromagnetic field's expression is derived for fixed Loop Source on Multilayered.2. Then, the arithmetic is proved to be feasible and correct by making contrastive research between the center point of the center loop's transient electromagnetic response and the center point of the fixed Loop's transient electromagnetic response using several groups of the earth model.At the same time,making the circular loop response equivalent to the square loop response,the forward computing time is decreased greatly. This can provide theoretical basis for the field data's inversion.3.Caculate the late time apparent resistivity of the large fixed loop.Using the apparent resistivity to interpret is more visually than using the response voltage,and the apparent resistivity can also be the initial model for the field data's inversion.4.Study the generalized inverse theory and singular value decomposition(SVD),compare the SVD method and the damping least square method,and use a new method called damping truncated singular value decomposition(DTSVD) method that can get the mutual complementary of the two methods,reduce the need of the precisiion for initial model parameter estimation,increase the convergence rate,make the inversion time shorter. 5. Simple and easy to operate to TEM inversion for the fixed loop source on layered earth graphical user interface is designed with the graphical user interface tool of MATLAB.6.By fitting the TEM data of the theoretical model with the damping truncated singular value decomposition, we find that the fitting rate is fast,the fitting result is correct, the inversion arithmetic is proved to be feasible.7.We studied the DTSVD method inversion for the wild transient electromagnetic data in Erlianhaote in the Inner Mongolia.By making the contrast between the sectional drawing of apparent resistivity , we found that the result was agreetable.the inversion arithmetic is proved to be feasible in the pratical application.