Improved application of remote referencing data in aeromagnetic processing: insights and applications from global geomagnetic modelling

地磁场测量是经济资源勘查的重要工具。航磁或海洋磁力调查相对便宜，也容易进行，但解释收集的数据并不直接。该磁场由地核发电机、在地球外部区域(电离层和磁层)流动的电流以及地壳和地幔中的磁性物质组成。这是潜在的经济利益，但为了使用磁测量，必须对其他来源进行校正。特别重要的是要对快速变化的外场进行校正。最常见的情况是，这是通过一个称为“远程引用”的过程来实现的。在被测量区域附近或内部安装固定磁力计，从测量测量中减去该固定仪器的读数。为此，假定外场必须在基准站和测量位置处相同(或接近)。这一假设并不坏，多年来一直很好地服务于该行业，但在当前具有重大经济利益的一些地理区域(赤道附近，以及北纬60度以上的高纬度地区)，这种假设就不那么好了。然而，电磁感应带来了更复杂的情况：外部磁场穿透地壳的导电区域，感应电流，进而产生更多磁场。由于电导率可以在短长度尺度上变化，所以两个位置的电场相同的假设就失效了。不正确的远程参考可能会将外部或感应场的变化误解为静态磁异常，从而提供潜在经济资源的错误图景。在这个项目中，我们将应用最近专门的卫星飞行任务所产生的对地磁场所有组成部分的更多了解。丹麦的Oersted宇宙飞船(1999年发射)和德国的CHAMP宇宙飞船(2000年发射)仍在收集近地轨道的磁力数据。这些数据彻底改变了我们对地磁场各个组成部分的详细了解；这项提议的目的是将这一新的理解应用于改进勘探磁力测量数据的处理方法，特别是改进通过实地模型预测和地面和航天器平台的同时测量进行远程参考的过程。来自即将到来的欧空局多卫星飞行任务群的数据将特别有用；这项任务将于2010年发射，因此将与学生时期重叠。

Measuring the geomagnetic field is an important tool in prospection for economic resources. Aeromagnetic or marine magnetic surveys are comparatively cheap and easy to conduct, but interpreting the data collected is not straight forward. The field is made up of contributions from the dynamo in the Earth's core, currents flowing in regions external to Earth (the ionosphere and magnetosphere), and magnetised material in the Earth's crust and mantle. It is this last that is of potential economic interest, but in order to use magnetic measurements, the other sources must be corrected for. It is particularly important to correct for the rapidly varying external field. Most commonly, this is achieved by a process called 'Remote referencing'. A fixed magnetometer is installed near or within the area to be surveyed, and the readings from that fixed instrument are subtracted from the survey measurements. For this to work, it is assumed that the external field must be the same (or close) at the base station and the survey location. This assumption is not bad, and has served the industry well for many years, but it less good in some geographical areas of great current economic interest (near the equator, and also at high latitudes above about 60 degrees latitude). However, a further complication is provided by electromagnetic induction: the external fields penetrate electrically conducting regions of the Earth's crust, inducing electric currents that in turn generate more magnetic fields. Because electrical conductivity can vary on short length scales, the assumption that the field in the two locations is the same breaks down. Incorrect remote referencing risks changes in the external or induced field being misinterpreted as static magnetic anomalies, so providing a false picture of the potential economic resources. In this project, we will apply the increased understanding of all components of the geomagnetic field that has arisen from recent dedicated satellite missions. Both the Danish Oersted spacecraft (launched in 1999) and the German CHAMP spacecraft (launched in 2000) are still collecting magnetic data from low Earth orbit. These data have revolutionised our detailed understanding of the various components of the geomagnetic field; the aim of this proposal is to bring this new understanding to bear in improving methods of processing of exploration magnetic survey data, in particular to improve the process of remote referencing with both predictions from field models and simultaneous measurements from ground and spacecraft platforms. Data from the upcoming ESA multi-satellite mission Swarm will be of particular use; this mission is due to be launched in 2010, and so will overlap will with the period of the studentship.