大定源瞬变电磁法三维正演程序开发

大定源瞬变电磁法是应用比较广泛的电磁激发方法之一，本文介绍了其三维正演程序的开发。首先从麦克斯韦方程组出发，通过讨论边界条件、初始条件和场源计算等问题，建立起地下半空间介质中电磁场与电阻率分布之间的关系方程。再论述求解地下半空间介质中电磁场的三维交错网格有限差分法。然后利用有限差分法完成大定源瞬变电磁法三维正演模拟程序的开发，并详细介绍了程序的流程。最后以均匀半空间模型为例来进行数值模拟，得出结论与实际相符合。利用该程序还可以设置各种三维地电模型来进行数值模拟，从而为野外勘察提供指导，为室内资料处理提供依据。

Program Exploitation on 3D Forward of Large Fixed Loop TEM

Large Fixed Loop TEM is one of the electromagnetism stimulation methods,which is widely used.This paper introduces its program exploitation on 3D forward.Firstly,from the Maxwell system of equations,it discusses the boundary condition,the initial condition and the field source computation.Secondly,it establishes the relational equation between electromagnetic field and resistivity distribution of underground half space medium.Thirdly,it elaborates 3D staggered-mesh finite difference method of solving the electromagnetic underground half space medium.Fourthly,it completes the program exploitation on 3D forward of Large Fixed Loop TEM using finite difference method,and introduces the procedure flow in detail.Finally it makes the value simulation taking the half space model as an example and shows the result is corresponding with the practical application.