3-D inversion of transient EM data with topography using unstructured tetrahedral grids
3-D inversion of transient EM data with topography using unstructured tetrahedral grids
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使用非结构化四面体网格对瞬态电磁数据进行地形三维反演
DOI：
10.1093/gji/ggz014
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发表时间：
2019-04
影响因子：
2.8
通讯作者：
Weng Aihua
中科院分区：
文献类型：
--
作者：
Liu Yunhe;Yin Changchun;Qiu Changkai;Hui Zhejian;Zhang Bo;Ren Xiuyan;Weng Aihua
山区瞬变电磁资料受地形影响严重，在资料解释中考虑地形影响是十分必要的。针对这一问题，本文提出了一种通过模拟地形来反演TEM数据的新方法。采用具有柔性的非结构化四面体网格对模型进行离散，以描述复杂地形。发射源包括磁环源和有限长电偶极子源，通过将发射源分解为短电偶极子来模拟发射源的实际形状、大小和姿态。在数值模拟中，我们采用基于边界的有限元方法（FEM）在空间上离散的控制方程，和无条件稳定的二阶向后欧拉（BE）格式在时间上离散。最终的正演模拟方程迭代求解从初始字段的所有时间通道。直接求解器MUMPS被用来解决效率的正问题。对于阶跃波初始电场与模型参数有关的电源，灵敏度雅可比矩阵的计算得到了很好的解决。由于全通道正向建模矩阵是不对称的，我们使用向后递归方法来解决伴随正向问题。考虑到我们的计算设备的能力有限，我们采用有限内存的BFGS优化方法来完成我们的三维反演。反演算法首先测试两个合成的例子，一个与一个大的固定回路发射源和另一个与一个长的接地线源在半航空TEM调查。反演结果表明，该方法可以对地形较陡的瞬变电磁资料进行反演。利用山西省大地电磁资料对反演程序进行了验证，反演结果与地质及其它地球物理资料吻合较好。
The transient electromagnetic (TEM) data acquired in mountainous area are seriously affected by topography, implying that consideration of topographic effect in the interpretation is in urgent need. To deal with this problem, we propose a new method to invert TEM data by simulating the topography. The unstructured tetrahedral grid with flexibility to delineate the rugged topography is adopted to discretize the inverse model. The transmitting source, including magnetic-loop and finite-length electric dipole source, is divided into short electric dipoles to simulate its practical shape, size and attitude. In the numerical simulation, we adopt the edge-based finite-element method (FEM) to discretize the governing equation in space, and the unconditional stable second-order of backward Euler (BE) scheme to discretize in time. The final forward modelling equation is solved iteratively from an initial field for all time channels. The direct solver MUMPS is used to solve the forward problem for efficiency. The calculation of Jacobian matrix of sensitivities is well addressed, especially for the electric source whose initial electric field for a step-off wave is related to the model parameters. Since the full-channel forward modelling matrix is asymmetric, we use a backward recursive method to solve the adjoint forward problem. Considering the limited power of our computational devices, we apply the limited-memory BFGS optimization method to accomplish our 3-D inversion. The inversion algorithm is firstly tested on two synthetic examples, one with a large fixed-loop transmitting source and the other with a long grounded line source as in semi-airborne TEM survey. The inversion results show that the proposed inversion scheme can invert TEM data with sharp topography. The inversion code is further tested on a ground TEM survey data acquired in Shanxi province, China and the results agree well with the geology and other geophysical information.
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影响因子：
2.8
作者：
Feiyan Wang;J. P. Morten;K. Spitzer
通讯作者：
Feiyan Wang;J. P. Morten;K. Spitzer
影响因子：
3.3
作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
Zhdanov Michael S.
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影响因子：
3.3
作者：
Changchun Yin;Bo Zhang;Yunhe Liu;Jing Cai
通讯作者：
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