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Stretching AEM Near-surface Resolution Limits Related to Low- and Very High Resistivity ContrastsNormal access

Authors: G.H. Skurdal, A.A. Pfaffhuber, A. Davis, S. Bazin, H. Anschütz, N.S. Nyboe, N. Foged, T. Thomassen and T. Wiig
Event name: Second European Airborne Electromagnetics Conference
Session: System Developments
Publication date: 03 September 2017
DOI: 10.3997/2214-4609.201702158
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 1.07Mb )
Price: € 20

Summary:
Data from AEM surveys carried out in Norway, to support ground investigations for infrastructure projects, was used in this study. In large infrastructure projects knowledge of sediment thickness is vital, as is information about possible occurrence of highly sensitive clay. In an area with conductive shales over resistive bedrock, the recently introduced system response method was tested. It's applied in the inversion of SkyTEM data and makes it possible to utilize the very earliest gates. The models showed to give more pronounced structures in the near-surface, reflecting true structures observed in resistivity borehole measurements. The same outcome was observed when conducting synthetic modelling. In another setting AEM measurements were carried out along a planned road project to provide information about the extent of very conductive, possible alum shale. A volume estimate of excavated masses was sought, as alum shale is decomposed to sulfuric acid by weathering. Preliminary AEM models had a tendency to overestimate the thickness of the resistive overburden. Experimenting with the inversion settings resulted in models better fitting other prior information from the area. Limited LM data was available due to a noisy environment. This affected the reliability of the models, illustrated by modelling and resulting real models.


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