大地电磁三维模型的一维二维反演近似问题研究

RESEARCH ON INVERSION OF MT3D MODEL APPROXIMATELY BY 1D,2D INVERSION METHOD

设计了一个简单的三维模型———均匀半空间的三维低阻异常体模型。采用51×51×38的网格计算得到了33.333Hz至0.0071Hz之间共34个频率的三维正演响应。选取其中5条具有代表性的测线,比较了不同测线上自适应正则化(ARIA)一维反演结果和非线性共轭梯度法(NLCG)二维反演结果相互之间及其与原三维理论模型之间的异同,研究大地电磁三维模型的一维、二维反演的近似情况。发现:对于三维模型响应,一维、二维反演都能得到反映模型真实信息的结果,但二维模型对三维模型的近似程度比一维模型要高得多;在二维模型反演中,采用TM模式更易得到真实的模型信息。研究中,采用蒲兴华等(1994)开发的MT三维正演程序进行正演计算,采用“大地电磁数据管理器(MTDATAMNG)”软件进行数据处理和一维、二维反演。

In this paper, a simple 3d model, low-resistivity abnormity 3 -d model in half space, is designed. Responses of 34 frequencies from 33. 333Hz to 0. 0071Hz are obtained in 3 - d modeling with 51 51 38 grids. 5 representational lines are adopted to study approximating 3 -d model with 1 -d, 2 -d inversion results. Results of 1 d inversion, 2 d inversion for each line are computed, and are compared with each other and with the original model. Studies show that both 1 -d and 2 -d inversion results contain true 3 -d model information, but the 2 - d inversion is far more approached to 3 - d model than ld inversion. Further more, when approaching 3 - d models with 2 - d inversion, it is the TM polarization mode data rather than the TE polarization mode data that should be adopted. The 3 - d modeling program used in this paper was developed by Dr. PU Xing - hua. The new visual integrated system, MTDATAMNG, is used in data processing and inversion. The 1 - d inversion method is adaptive regularized inversion algorithm （ARIA）, and 2 - d inversion method is nonlinear conjugate gradients algorithm （NLCG）.