3D inversion of airborne electromagnetic data using a moving footprint
Leif H. Cox 1 2 Glenn A. Wilson 2 4 Michael S. Zhdanov 2 3
+ Author Affiliations
- Author Affiliations
1 Department of Geophysical Engineering, Montana Tech, 1300 West Park Street, Butte, MT 59701, USA.
2 TechnoImaging, 4001 South, 700 East, Suite 500, Salt Lake City, UT 84107, USA.
3 Department of Geology and Geophysics, The University of Utah, 1450 East, 100 South, Salt Lake City, UT 84102, USA.
4 Corresponding author. Email: glenn@technoimaging.com
Exploration Geophysics 41(4) 250-259 https://doi.org/10.1071/EG10003
Submitted: 18 January 2010 Accepted: 19 November 2010 Published: 15 December 2010
Abstract
It is often argued that 3D inversion of entire airborne electromagnetic (AEM) surveys is impractical, and that 1D methods provide the only viable option for quantitative interpretation. However, real geological formations are 3D by nature and 3D inversion is required to produce accurate images of the subsurface. To that end, we show that it is practical to invert entire AEM surveys to 3D conductivity models with hundreds of thousands if not millions of elements. The key to solving a 3D AEM inversion problem is the application of a moving footprint approach. We have exploited the fact that the area of the footprint of an AEM system is significantly smaller than the area of an AEM survey, and developed a robust 3D inversion method that uses a moving footprint. Our implementation is based on the 3D integral equation method for computing data and sensitivities, and uses the re-weighted regularised conjugate gradient method for minimising the objective functional. We demonstrate our methodology with the 3D inversion of AEM data acquired for salinity mapping over the Bookpurnong Irrigation District in South Australia. We have inverted 146 line km of RESOLVE data for a 3D conductivity model with ~310 000 elements in 45 min using just five processors of a multi-processor workstation.
Key words: 3D, airborne, Bookpurnong, electromagnetic, footprint, inversion, regularisation, RESOLVE.
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