The spectral-element (SE) method, which is based on the Galerkin technique, has been gradually implemented in geophysical electromagnetic (EM) 3D simulation. The accuracy and efficiency of this approach, implemented for deformed hexahedral and regular meshes, has been verified for airborne EM forward modeling. One advantage of the SE method over the conventional finite-element method is that it provides accurate results for earth models that can be adequately parameterized using a coarse mesh. However, realistic models can contain important small-scale conductivity variations or larger features with complicated boundaries. To overcome the limitations imposed by using the same mesh to parameterize the model and for implementing the forward-modeling approach, we have developed an adaptation of the conventional SE method. This is inspired by the ideas behind the element-free Galerkin (EFG) method, in which the conductivity is no longer assumed to be constant within a cell; instead, it is handled via the same kind of numerical integration as in the EFG method. This allows a coarse, regular hexahedral mesh to be used for the forward modeling for complex earth models. After presenting the theory for this new SE approach, we test it for airborne EM modeling of 1D and 3D models to verify its flexibility and accuracy. Finally, we model the Ovoid Zone massive sulfide ore body located at Voisey’s Bay, Labrador, Canada, to illustrate the flexibility and practicality of our approach.

中文翻译：

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一种使用改进谱元法的机载电磁数据的 3D 正向建模方法

基于伽辽金技术的谱元 (SE) 方法已逐渐应用于地球物理电磁 (EM) 3D 模拟。这种为变形六面体和规则网格实施的方法的准确性和效率已在机载电磁正演建模中得到验证。与传统有限元方法相比，SE 方法的一个优点是它可以为地球模型提供准确的结果，这些结果可以使用粗网格进行充分参数化。然而，现实模型可能包含重要的小尺度电导率变化或具有复杂边界的更大特征。为了克服使用相同网格参数化模型和实施正向建模方法所带来的限制，我们开发了对传统 SE 方法的改编。这是受到无元素伽辽金 (EFG) 方法背后的想法的启发，在该方法中，不再假设电池内的电导率是恒定的；相反，它是通过与 EFG 方法中相同类型的数值积分来处理的。这允许将粗糙的规则六面体网格用于复杂地球模型的正向建模。在介绍了这种新 SE 方法的理论之后，我们针对 1D 和 3D 模型的机载 EM 建模对其进行了测试，以验证其灵活性和准确性。最后，我们对位于加拿大拉布拉多 Voisey's Bay 的 Ovoid Zone 块状硫化物矿体进行建模，以说明我们方法的灵活性和实用性。它是通过与 EFG 方法相同的数值积分来处理的。这允许将粗糙的规则六面体网格用于复杂地球模型的正向建模。在介绍了这种新 SE 方法的理论之后，我们针对 1D 和 3D 模型的机载 EM 建模对其进行了测试，以验证其灵活性和准确性。最后，我们对位于加拿大拉布拉多 Voisey's Bay 的 Ovoid Zone 块状硫化物矿体进行建模，以说明我们方法的灵活性和实用性。它是通过与 EFG 方法相同的数值积分来处理的。这允许将粗糙的规则六面体网格用于复杂地球模型的正向建模。在介绍了这种新 SE 方法的理论之后，我们针对 1D 和 3D 模型的机载 EM 建模对其进行了测试，以验证其灵活性和准确性。最后，我们对位于加拿大拉布拉多 Voisey's Bay 的 Ovoid Zone 块状硫化物矿体进行建模，以说明我们方法的灵活性和实用性。