Integrated interpretation of overlapping AEM datasets achieved through standardisation

Abstract

Numerous airborne electromagnetic surveys have been acquired in Australia using a variety of systems. It is not uncommon to find two or more surveys covering the same ground, but acquired using different systems and at different times. Being able to combine overlapping datasets and get a spatially coherent resistivity-depth image of the ground can assist geological interpretation, particularly when more subtle geophysical responses are important. Combining resistivity-depth models obtained from the inversion of airborne electromagnetic (AEM) data can be challenging, given differences in system configuration, geometry, flying height and preservation or monitoring of system acquisition parameters such as waveform. In this study, we define and apply an approach to overlapping AEM surveys, acquired by fixed wing and helicopter time domain electromagnetic (EM) systems flown in the vicinity of the Goulds Dam uranium deposit in the Frome Embayment, South Australia, with the aim of mapping the basement geometry and the extent of the Billeroo palaeovalley. Ground EM soundings were used to standardise the AEM data, although results indicated that only data from the REPTEM system needed to be corrected to bring the two surveys into agreement and to achieve coherent spatial resistivity-depth intervals.

Combining resistivity-depth models obtained from the inversion of airborne electromagnetic data can be challenging, but spatially coherent resistivity-depth images of the ground can assist geological interpretations. We use ground EM data to standardise AEM data so as to be able to combine overlapping AEM datasets acquired with different systems.

Key words::

• AEM
• calibration
• Goulds Dam uranium deposit
• REPTEM
• standardisation
• TEMPEST
• WalkTEM

Acknowledgements

Camilla Sørensen is in receipt of a scholarship from the Goyder Institute of Water Research, South Australia. The work was undertaken under the auspices of the Goyder FLOWS 1 Project. The authors acknowledge the support of UraniumOne who provided the TEMPEST data and without whose help this work would not have been possible. In particular we would like to thank Jason Cherry for his invaluable help and input into the work. The REPTEM data were provided by Red Metal Limited and we acknowledge their assistance in providing access to these data. The WalkTEM system was provided for research through the good offices of Aarhus University and Kurt Sorensen is thanked in this regard. We would also like to thank one of the reviewers for enlightening us on the challenges of ‘calibration’ versus ‘standardisation’ most notably in reference to the use of test sites and the average foot length of worshippers in the eastern North America.