Modelling and inversion of geophysical electromagnetic data

地球物理学的目标是理解，也许是预测，移动和塑造我们脚下地球的动态过程，并“观察”地球，看到这些过程的作用，或者它们的后果。一种利用电磁场对地下结构进行远程探测的技术，甚至可以探测到几十公里深的地下结构。在这种技术中，电流被诱导在岩石中流动。水流的强度和流向取决于岩石类型。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又产生可测量的电磁场。这些测量的强度和变化取决于感应电流，以及岩石本身。因此，有可能把测量结果颠倒过来，也就是说，把它们颠倒过来，提取有关地下岩石类型的信息。拟议的研究决定：(1)改进计算机程序所使用的数学，以便在已知地下岩石类型的情况下预测感应电流；(2)改进反演电磁场测量以生成地球结构模型的程序。最近的进展已经产生了第一代完全三维地球模型的程序。然而，这些程序用于地下岩石类型排列的数学表示是基本的，既不够灵活，无法处理自然界中发生的复杂结构，也不够精确，无法处理相邻岩石类型之间的巨大变化，而这些变化可能存在于某些重要特征，如矿床。本研究计划将研究使用更复杂和更精细的地下表示来克服这些问题。结果将是计算机程序可以提供更详细、更可靠的地下模型或“图像”。这些项目将对采矿业有用，有助于发现新的矿藏。它们还将用于遥感地下水资源、岩土工程应用和确定地壳的深层结构。

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.