基于全区视电阻率的线源FCSEM二维正演模拟

频率域可控源电磁是在大地电磁测深的基础上发展起来的一种人工源电磁测深法,其二维电磁响应的计算须采用数值模拟方法.本文以Matlab为程序编译工具,采用双二次插值的有限单元法,推导出相应的计算公式.为了模拟无穷远边界及满足计算机的内存需求,在保证计算精度的情况下设计了非均匀网格剖分.在程序编制中,只存储有限元系数矩阵的非零元素,大大减少了正演计算的时间.针对频率域可控源电磁法中卡尼亚电阻率在过渡区和近区畸变的问题,给出了全区视电阻率的迭代公式,并对典型的一维层状模型以及简单二维模型进行了计算.过渡区和近区数据经过校正后,可以正确反映出模型的地电特征,证明了线源下近区勘探的可能性.

Line sources FCSEM two-dimensional forward modeling based on the all-time apparent resistivity

Frequency domain controlled-source electromagnetic(FCSEM) is an artificial source electromagnetic sounding method,which developed on the basis of magnetotelluric sounding.In order to show the FCSEM forward modeling result,numerical simulation method must be adopted.In this paper,base on Matlab as a programming tool,we adopted the finite element method of quadratic interpolation in a rectangular element for solving the FCSEM forward problem and derived the corresponding formula for calculating.In order to simulate the infinity border and meet the demand computer memory,the non-uniform gird is designed with ensuring the accuracy.In programming,we only stored the non-zero elements of the finite element matrix which can reduce the forward calculation time.The iterative formula of the all-time apparent resistivity was developed to solving the problem of distortion of Cagniard apparent resistivity when the dates are collected near the source.Typical 1D layered model and simple 2D model are calculated.After rectify the date,it can accurately reflect the characteristics of the model which verified the fact that the exploration near the source is possible.