Accurate AEM Data Processing in Hydrogeological Projects… Is It Worth the Time and $ ?

Abstract

Airborne Electromagnetics (AEM) is increasingly being used across the globe as a tool for groundwater and environmental management. To name a few, the geological surveys of Denmark and Australia, have acquired large datasets for these applications. In both countries particular focus is given to ensuring the quality of the source data, their processing and modeling, and the integration of results with ancillary information in order to generate accurate and relevant products. In this paper we examine the consequences that different levels of processing of Helicopter TEM data have on the resulting electrical models and subsequently on hydrogeological models. We use a SkyTEM dataset from Sommersted in Denmark, acquired in 2008. We focus on different approaches used in the industry for processing of the raw data whereas the inversion, which is necessary to show the effect in the model space, is undertaken in rather standard way. We show how the electrical models and the hydrogeology change with 1) the level of decoupling of artifacts, 2) lateral averaging and 3) late time noise assessment and we compare the outcomes with available borehole information. Each one of these processing steps alters the output, and therefore the derived models. The consequence of e.g. under/overestimating the depth to bedrock by several tens of meters, or the absolute resistivities by hundreds of Ohmm, could be assigning the wrong hydrogeological unit to a given electrical layer. We contend that the extra resources in time, effort and money required to obtain more accurate models of the subsurface are warranted.