On the use of legacy AEM data

Abstract

The term ‘legacy data’ is rather loose. It always means ‘old data’, but there is no consensus on what is ‘old’, especially across disciplines/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.