On the use of legacy AEM data
The term ‘legacy data’ is rather loose. It always means ‘old data’, but there is no consensus on what is ‘old’, especially across dis-ciplines/data types. In this paper we focus on Time domain AEM data post 2000. By then, virtually all systems were equipped with a Digital Aquisition System (DAS). It is also around those years that Time Domain (TD) systems started to gain ground on Frequency Domain (FD) systems, thanks to the introduction of concentric helicopter borne systems. However, it is time domain systems that can most benefit from renewed analysis modelling. Time domain data can take longer to model, which is one of the reasons they were often never properly inverted at the time. On the other hand, they often span larger frequency ranges (3-4 decades instead of 2-3 of the FD) while also displaying clearer signatures of ‘new’ physical processes such as Airborne IP (AIP) and superparamagnetic effects (SPM). Finally, most development in new generation of AEM systems takes place in TD, which fosters continued R/D. There are several good reasons to give another look at ‘legacy’ AEM data. First of all, the largest part of the investment (i.e., data aquisi-tion) has already been undertaken; secondly, the datasets are often very sub-utilized; thirdly, as mentioned above, there is strong Research and Development that is enabling us to understand phe-nomena which were previously flagged as noise, or disregarded; fourthly, we witness the push for integrating data from different sources; last, but not least, the huge amount of spatial data asso-ciated with AEM represent a formidable attraction to big data-AI. Here we touch briefly on two aspects of the benefits of reinspecting legacy AEM data: general geological mapping and modelling IP effects.