Spatially constrained inversion for quasi 3D modelling of airborne electromagnetic data – an application for environmental assessment in the Lower Murray Region of South Australia

Andrea Viezzoli; Esben Auken; Tim Munday

doi:10.1071/EG08027

RESEARCH ARTICLE

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Spatially constrained inversion for quasi 3D modelling of airborne electromagnetic data – an application for environmental assessment in the Lower Murray Region of South Australia

Andrea Viezzoli ¹ ³ Esben Auken ¹ Tim Munday ²

+ Author Affiliations

- Author Affiliations

¹ Department of Earth Sciences, University of Aarhus, Høegh-Gulbergs Gade 2, Aarhus C 8000, Denmark.

² CSIRO, ARRC, 26 Dick Perry Avenue, Kensington, WA 6151, Australia.

³ Corresponding author. Email: andrea.viezzoli@geo.au.dk

Exploration Geophysics 40(2) 173-183 https://doi.org/10.1071/EG08027
Submitted: 16 December 2008 Published: 17 June 2009

Abstract

We present an application of spatially constrained inversion (SCI) of SkyTEM (airborne electromagnetic) data for defining spatial patterns of salinisation in the Bookpurnong irrigation area located in the lower Murray Basin of South Australia. SCI uses Delaunay triangulation to set 3D constraints between neighbouring soundings, taking advantage of the spatial coherency that may be present in the dataset. Conductivity information for individual soundings is linked through the spatial constraints, from well determined parameters to locally poorly determined parameters. For the survey presented here, SCI generated maps detail the spatial variability of floodplain salinisation, the extent of floodplain sediments influenced by lateral recharge and flushing along stretches of the Murray River, and the variable quality of groundwater in deeper semi-confined aquifers of the Murray Group. Available borehole and other ancillary information, such as vegetation density and health patterns, match the observed conductivity variations seen in the SCI results, even at the very near surface (≈2m depth). The SCI provides more accurate and spatially consistent results compared with those from single site inversions. They are also more uniform and detailed than maps obtained with single point Layered Earth Inversions or a laterally constrained inversion. In this example, the SCI provided reliable quasi 3D modelling, that confirmed and improved the hydrogeological knowledge of the area, indicating that the technique would have application with helicopter electromagnetic data in similar settings throughout the lower Murray Basin of Australia.

Key words: airborne electromagnetic, quasi 3D, salinisation, SkyTEM, spatially constrained inversion.

Acknowledgments

The Bookpurnong SkyTEM data were acquired as part of SA CNRM project #054127: The application of airborne geophysics to the prediction of groundwater recharge and floodplain salinity management. TJM’s contribution to this study was undertaken as part of that project and their support is acknowledged. This work was also supported by the CSIRO-led Water for a Healthy Country Flagship. The authors also acknowledge the assistance of Andrew Fitzpatrick, Kevin Cahill, Volmer Berens and Mike Hatch in the conduct of work at Bookpurnong. Kevin Cahill was particularly helpful with the presentation of the data.

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