三维电阻率测深数据Zohdy近似反演方法

Zohdy方法近似反演三维电阻率测深数据。正演计算采用有限单元法。反演初始模型由测量视电阻率数据给出。通过比较实测视电阻率值和预测模型计算的视电阻率值对数差来修改模型网格电阻率．为了解决任意电极距测深数据的反演，采用大、小双网格剖分。大网格反映地下电性分布情况。小网格用于实际有限元正演计算．在电阻率调整公式中加入一个迭代系数，能够加快收敛速度．并对加5％随机噪声的模型理论视电阻率测深断面数据进行反演，得到的电阻率分布与模型电阻率基本一致．

Approximate inversion on three-dimensional resistivity sounding data

Three-dimensional resistivity sounding data are approximately inversed by Zohdy method. The FEM is used for forward solution, and the initial electrical parameters of the earth are obtained from observed data or forward data of earth model and modified by the logarithic difference between observed data and the theoretical data calculated by the finite element forward solution. Two kinds of grid system is employed to solve the problem arose from the arbitrary electrode-spacing. The big grid pictures resistivity distribution of earth model and the small one is used to define elements in forward solution. In addition, the iteration coefficient is added to resistivity adjustment formula so that the convergence velocity has obvious improvement in the course of inversion. Finally, the theoretical data, added 5% random noise, obtained from three-dimensional earth model is inversed. Which proves that it is a practical method.