The Multi-component Interpretation Technology Of Transient Electromagnetic Method

The multi-component interpretation technology of transient electromagnetic method (TEM) is helpful to the application of TEM sounding in the project survey, the tunnel prediction ,the investigation of coalfield geological disasters, and so on.Transient electromagnetic sounding method is always interpreted by the vertical component of the central point. However, there are a few measuring points acquired when surveying in road tunnels, railway tunnels and coal fields. With a few collection points of vertical component measurement, it will definitely affect the accuracy of detection and the explanation work will be more difficult. To improve the detection accuracy is bound to increase the number of measuring points, therefore, collecting the field value of multi-component is very necessary.This paper studied the numerical calculating method of both the vertical and the horizontal component response of the magnetic field under different offset, in the uniform and layered medium, by the large loop exciting source. Also, this paper pushed over the expression of apparent resistivity defined by the vertical component and horizontal component, and provided theoretical basis for the multi-component interpretation technology of transient electromagnetic method.The calculation method of Sommerfeld integrals was first discussed, through which obtained the frequency function of each component of non-central point under different offset. Then the two functions were compared with the vertical component of the central point, and it was found that they had the same form. The polynomials and their coefficients were obtained respectively with the curve-fitting method and the least square method. The expression of the apparent resistivity of non-central point was defined by the same method as the vertical component at the centre point. At last, using the apparent resistivity expressions, which derived from the method above, explained the actual data in the model, and compared with the vertical component in the central point, and the result showed that the multi-component interpretation technology of transient electromagnetic method not only improved the accuracy of exploration, but also distinctly displayed the boundary of the low resistivity body.