Study On Detection Ability Of Rectangular-loop TEM

Electromagnetic method is a kind of geophysical methodology widely used in exploration of mineral resources and environmental hydrogeology, which can be divided into two kinds:those are frequency domain electromagnetic methods and time domain electromagnetic methods. Transient Electromagnetic Method (referred to as TEM) belongs to the time domain electromagnetic method. Since1951, for two decades’ continuous and rapid development, it had achieved considerable progress in theoretical research and application. But forward and inversion of multidimensional problems is very time-consuming and requires high capability of hardware, field data processing and interpretation is still of low level for the1-D interpretation. So studying detection capability of TEM is the key to improve the level of its interpretation.(1) Starting from frequency domain field excited by vertical magnetic dipole, we deduced the expressions of frequency domain field excited by rectangular loop in terms of loop area integral for magnetic moment. And then we obtained expressions of response to the magnetite according to G-S algorithm and Faraday’s law of electromagnetic induction. On the basis of this, we calculated geoelectric models with different ratio of buried depth to thickness and resistivity contrast, then comparative analysis on the error are contrasted in detail by using all time apparent resistivity. Finally, resolution limit of which the loop-source TEM detects thin layer of low and high resistance is given.(2) Through finite-difference time-domain (FDTD) calculation for3-D transient electromagnetic field, we studied the characteristics and attenuation law of curves for three-component excited by rectangular loop in homogeneous half-space. Then we made comparison and analysis of three-component curves which are response of conductive thin plate with different angles, different resistivity, different depth and different position. Finally, correlation method was summarized to judge scale and occurrence of anomalous body using amplitude and morphology of three-component.