Controlled‐source electromagnetic methods are applied to survey the electrical resistivity distribution of the subsurface. This work compares normalized electromagnetic field components and transfer functions such as impedance tensors and vertical magnetic transfer functions generated by two independent source polarizations as input data for three‐dimensional inversion. As most other available inversion codes allow for inverting only one of the mentioned input data types, it is unclear which data type is preferable for controlled‐source electromagnetic inversion. Our three‐dimensional non‐linear conjugate gradient inversion code can handle both input data types, facilitating a comparison of normalized electromagnetic field components and transfer functions inversion. Examining inversion results for a three‐dimensional synthetic model with two anomalies, we infer that the transfer functions inversion is favourable for recovering the overall resistivity distribution below the receiver sites in fewer iterations. The inversion of normalized electromagnetic field components produces a sharper image of the anomalies and may be capable of detecting the resistivity distribution below the extended sources, which comes at the price of introducing a more heterogeneous background resistivity in the model.

中文翻译：

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研究报告：归一化受控源电磁场分量和传递函数作为三维非线性共轭梯度反演输入数据的比较

应用受控源电磁方法来测量地下的电阻率分布。这项工作比较了归一化电磁场分量和传递函数，例如由两个独立源极化生成的阻抗张量和垂直磁传递函数，作为三维反演的输入数据。由于大多数其他可用的反演代码仅允许反演上述输入数据类型之一，因此尚不清楚哪种数据类型更适合受控源电磁反演。我们的三维非线性共轭梯度反演代码可以处理两种输入数据类型，便于比较归一化电磁场分量和传递函数反演。检查具有两个异常的三维合成模型的反演结果，我们推断传递函数反演有利于以较少的迭代次数恢复接收点下方的整体电阻率分布。归一化电磁场分量的反演产生更清晰的异常图像，并且能够检测扩展源下方的电阻率分布，这是以在模型中引入更加不均匀的背景电阻率为代价的。