The Study Of Forward Modeling And Rapid Imaging To A Magnetic Dipole Source

The electromagnetic method of magnetic dipole source is a portable and expeditious geophysical method. Its range of application is wide, presently, this method was used in mineral prospecting, engineering exploration, archeology detection, UXO location and soil conductivity measurement etc. The thesis mainly discuss and study the forward modeling and rapid imaging about vertical magnetic dipole source which is the most familiar method in production.(1) One-dimensional forward: The thesis derives the electromagnetic expressions that a vertical magnetic dipole source in homogeneous conductive full-space, the electromagnetic expressions that a vertical magnetic dipole source on layered half-space and the electromagnetic expressions that a vertical magnetic dipole source on homogeneous conductive half-space. According to these electromagnetic expressions, this thesis accomplishes the forward modeling about homogeneous conductive half-space and layered half-space(the target layer's resistivity is low). The result is: When we accomplishes the forward modeling about homogeneous conductive half-space, the value of vertical magnetic field would decreased along with the pole distance increases. (And the higher the frequency is, the faster the value decreases); When we accomplishes the forward modeling about layered half-space, the response is not obvious of the target layer when the pole distance is in near region and middle region, but the response is obvious of the target layer when the pole distance is in far region.(2) 2.5-dimensional forward: The main principle of this forward modeling method is to synthesize data for three-dimensional source with a series of different wave numbers in geologic structure's strike direction based on Fourier transform, and then, calculate a series of discrete wave numbers field use the finite difference method, lastly, we can gain the three-dimensional field response, accomplish 2.5-dimensional forward modeling after inverse Fourier transform. We have simulated some typical models, and analyzed the results. The result is: When the model is single, for horizontal plate, we can gain different results when we change the length of plate, the buried depth of plate and the pole distance; for gradient plate, whether the trend of the plate is left or right, the response is obvious. When the model is unitized, the result of response is good, too.(3) Rapid Imaging: The probability tomography method which has successfully used in Self-Potential Method (SP) and Magnetotelluric Method (MT) was introduced in this study. This method has some excellent characteristics: simplicity, the calculated amount is small, having no use for forward-inversion iterative process like conventional inversion. We process some typical models and actual data, the result is satisfying. But some detail need ameliorate, for instance, when we process horizontal plate and vertical plate, the result of imaging is not symmetrical. And when we process actual data, the effect of some detail is not perfect.