From Manual to Automatic AEM Bedrock Mapping

Abstract

An extensive airborne electromagnetic (AEM) survey was carried out in Norway with the primary purpose to obtain information of depth to bedrock in areas with little or no prior geotechnical knowledge. We present different approaches to extract a bedrock model from the high-resolution time-domain AEM data, including both automated and manual procedures. It was found that in the area of investigation a user-driven approach of manual bedrock picking was the most suitable, taking into account the strongest vertical resistivity gradient and geological information as additional information. A semi-automatic, statistical method, called Localized Smart Interpretation (LSI), is also presented and discussed. This method, while not included in the original bedrock model for the entire area, showed promising results while using less time compared to the fully manual approach. It is recommended that LSI be considered in future projects of similar scope.

The emperor's new clothes - opportunities and limitations applying AEM to geotechnical design work

“…2015). For most of the data discussed here, we combine automatic and manual interpretation (Anschütz et. al.…”

“…Processing and inversion was done with the Århus Workbench spatially constrained inversion with moderately loose vertical and horizontal constraints and automatic starting models to account for the heterogeneous geology ranging from outcropping resistive bedrock to tens of meters with conductive, marine clay. Bedrock topography interpretation involved a combination of resistivity thresholds, vertical resistivity gradient, manual picking and sparse geotechnical boreholes (Anschütz et al 2016b).…”

Resistivity and chargeability survey for tunnel investigation: a case study on toxic black shale in Norway

“…, Anschütz et al . ). The typical size of an AEM survey for such projects is on the order of 200‐km flight lines, which takes approximately 2–3 days to fly.…”