中文摘要：

近年来,国内外学者对瞬变电磁法2.5维有限单元正演模拟进行了大量的研究.在前人研究的基础上给出了矩形回线源瞬变电磁法2.5维有限差分正演模拟算法.从磁场垂直分量满足的扩散方程入手,推导了瞬变电磁法2.5维有限差分正演计算的差分方程;通过正余弦变换、Gaver-Stehfest变换、反傅氏变换等数值方法求解了均匀半空间矩形回线源激发的波数域瞬变场,作为初始条件;推导了波数域磁场向上延拓的公式,作为地空边界条件.最终建立了瞬变电磁法2.5维有限差分正演模拟算法.通过与解析解、有限元数值解的对比以及对典型模型的正演模拟,证明了算法的正确性与有效性.

英文摘要：

In recent years,scholars at home and abroad have carried out a great deal of research on Finite element modeling of 2.5-D Transient Electromagnetic（TEM）.A numerical algorithm of Finite-difference method for 2.5-D TEM forward modeling for rectangular loop source has been develop on the basis of previous studies in this paper.From the diffusion equation of the vertical component of magnetic field,Derivation of the difference equation for the algorithm of 2.5-D TEM forward modeling was given.Being initial conditions,all expressions of TEM field in homogenerous half-space generated by a rectangle loop source in the air space were derived through the digital algorithm of sine and cosine transforms,GaverStehfest transform and the inverse Fourier transform etc.Being air-earth boundary conditions, expressions for upward continuation in wave domain were derived and solved.Eventually,the algorithm of Finite difference method for 2.5-D TEM forward modeling was built. The correctness and reliability of 2.5-D FDTD algorithm in this paper are proved by carring out the comparison between the numerical simulations and the 1Danalytical solution and and numerical solution of finite element as well as modeling of typical model.