Study Of Three-dimensional Forward Of TEM

Transient electromagnetic method (TEM) has been widely used in metal, oil and geothermal exploration of mineral resources, but also widely used in engineering, find bedrock and groundwater and the prevention of disasters, are increasingly shown its important position.Because relatively backward of explain technology, complex algorithm the inversion and forward of calculation requires a large amount of time and computer memory,and other factors, severely restrict the development of TEM. Therefore, it is theoretical and practical to study the transient electromagnetic response of three-dimensional(3-D)models. In addition, the 3-D TEM forward provided the necessary theoretical foundation and guidance for the inversion and explain of the 3-D electromagnetic method.At present the numerical simulation of electromagnetic method in the exploration commonly used finite difference method, finite element Method, boundary element law, integral equation method, and so on. In the time domain, finite difference is more convenient . In This paper, we give a significant step for the stability of the electromagnetic component of the finite difference equation . We used the staggered-grid scheme combining with a modified version of the Du fort-Frankel scheme to discretize the quasi-static Maxwell's equations. we calculated the initial value from the frequency domain electromagnetic field expressions of the homogeneous half-space surface vertical magnetic dipole , used the Laplacian transformation and the digital Hankel transform to strike a Bessel function integral to obtain the electric field analytical solution of step response in the time domain. For the boundary conditions, we are still extended the magnetic field in the air and imposed on the Dirichlet boundary conditions.We used two-dimensional Fourier transform to strike the magnetic components of free space . On account of the non-uniform grids, around the 2-D Fourier transform,magnetic field value need interpolation,here,we adopted a bicubic spline interpolation .After moving the transmit loop, we adopted Relative location and calculated magnetic field value by interpolation , thus avoiding the re-calculation of primary field.About the realization of algorithm ,We have implemented the program using Fortran and visualized the results using Matlab. Numerical solution for a homogeneous half-space, some 3-D models and models of fine conductive layer overburdened showed that the solution provides accurate results .Therefore, studying the 3-D modeling of non-uniform grids, is meaningful.