二次场算法对于可控源电磁地形问题的适用性研究
Research on the Applicability of Secondary Field Algorithm to Terrain Problems of Controlled-Source Electromagnetic Method

二次场算法常用于处理平坦地形下的可控源电磁正演问题，在海洋可控源领域也得到了广泛的应用。而关于二次场算法能否处理陆地起伏地形区域尚无定论。本文介绍了基于二次场的可控源三维正演算法在起伏地形模型下的建立过程和使用原理。通过电磁理论分析和多种模型的计算实例，分析了二次场算法在地形区域的正演结果异常及其产生的原因。最后通过对模型电导率和离散网格的控制变量实验，验证了二次场算法在地形区域的正演结果异常暂时无法通过有效手段解决。结果表明，在地空模型条件下，二次场正演算法暂时无法适用于绝大部分的起伏地形区域。
The secondary field algorithm is often used to deal with the forward modeling of Controlled- Sources Electromagnetic Method in flat terrain, and has also been widely used in the field of Marine Controlled-Sources Electromagnetic Method. However, there is still no conclusion on whether the secondary field algorithm can deal with the terrain region. In this paper, the establishment process and application principle of 3D forward modeling algorithm based on secondary field are introduced. Through the analysis of electromagnetic theory and calculation examples of various models, the forward results of secondary field algorithm in terrain region are analyzed and the causes are analyzed too. Finally, through the control variable experiments of the model conductivity and the discrete grid, it is verified that the forward anomaly of the secondary field algorithm in the terrain region cannot be solved by effective means. The results show that the secondary field algorithm cannot be applied to most of the undulating terrain regions under the condition of ground-air model.