Modelling and inversion of geophysical electromagnetic data

地球物理学的目标是了解，或许预测，在我们脚下移动和塑造地球的动态过程，并“观察”地球，看看这些过程在行动中，或它们的后果。一种遥感地下结构的技术，即使是在几十公里深的地方，也使用电磁场。在这项技术中，电流在岩石中感应流动。海流的强度和配置取决于岩石类型。例如，金属矿石的导电性相对较好。地面上的感应电流反过来会产生可以测量的电磁场。这些测量的强度和变化取决于感应电流等岩石本身。因此，有可能颠覆测量结果，也就是颠倒它们，并提取关于地下岩石类型的信息。这项拟议的研究决定(I)改进计算机程序使用的数学方法，以预测如果地下岩石类型已知，感应电流将是多少；以及(Ii)改进程序，将电磁场的测量结果倒置，以生成地球结构的模型。最近的进展已经产生了有效的第一代这些程序，用于完全三维的地球模型。然而，这些程序用于地下岩石类型排列的数学表示法是基本的，既不足以灵活地处理自然界中出现的复杂结构，也不足以精确地处理相邻岩石类型之间的巨大变化，这些变化可能是针对某些重要特征(如矿床)而存在的。这项研究计划将调查如何使用更复杂和精致的地下表示法来克服这些问题。其结果将是计算机程序，可以提供更详细、更可靠的地下表面模型或“图像”。这些项目将对采矿业有用，使新的矿藏得以发现。它们还将在遥感地下水资源、岩土工程应用以及确定地壳深层结构方面发挥作用。

The goal of geophysics is to understand, and perhaps predict, the dynamic processes that move and shape the Earth beneath our feet, and to "look" into the Earth to see these processes in action, or their consequences. One technique for remotely sensing what the structure of the subsurface is, even to depths of tens of kilometres, uses electromagnetic fields. In this technique, electric currents are induced to flow in the rocks. The strength and disposition of the currents depend on rock type. Metallic ores, for example, are relatively good at conducting electricity. The induced currents in the ground give rise, in turn, to electromagnetic fields which can be measured. The strengths and variations of these measurements depend on the induced currents, and so on the rocks themselves. It is therefore possible to turn the measurements on their heads, that is, invert them, and extract information about what the rock types are in the subsurface. The proposed research determines to (i) improve the mathematics used by computer programs to predict what the induced currents would be if the rock types in the subsurface were known, and (ii) improve the programs that invert measurements of the electromagnetic fields to generate models of the structure of the Earth. Recent advances have produced what is effectively the first generation of these programs for fully three-dimensional models of the Earth. However, the mathematical representations these programs use for the arrangements of rock types in the subsurface are basic, being neither flexible enough to cope with the complicated structures that occur in nature, nor precise enough to handle the dramatic changes between adjacent rock types that can exist for certain important features such as ore deposits. This research programme will investigate the use of more sophisticated and refined representations of the subsurface to overcome these problems. The result will be computer programs that can provide more detailed and more reliable models, or "images", of the subsurface. These programs will be of use to the mining industry, enabling new ore deposits to be found. They will also be of use in remotely sensing groundwater resources, geotechnical applications, and in determining the deep structure of the Earth's crust.