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Journal of the Australian Society of Exploration Geophysicists
RESEARCH ARTICLE

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.


References

Auken, E., Chistiansen, A. V., Jacobsen, B. H., Foged, N., and Sorensen, K. L., 2005, Piece-wise 1D laterally constrained inversion of resistivity data: Geophysical Prospecting, 53, 497–506
Piece-wise 1D laterally constrained inversion of resistivity data:Crossref | GoogleScholarGoogle Scholar |

Beamish, D., 2003, Airborne EM footprints: Geophysical Prospecting, 51, 49–60
Airborne EM footprints:Crossref | GoogleScholarGoogle Scholar |

Brodie, R., and Sambridge, M., 2006, A holistic approach to inversion of frequency-domain airborne EM data: Geophysics, 71, G301–G312
A holistic approach to inversion of frequency-domain airborne EM data:Crossref | GoogleScholarGoogle Scholar |

Brodie, R., and Sambridge, M., 2009, Holistic inversion of frequency-domain airborne electromagnetic data with minimal prior information: Exploration Geophysics, 40, 8–16
Holistic inversion of frequency-domain airborne electromagnetic data with minimal prior information:Crossref | GoogleScholarGoogle Scholar |

Chen, J., and Raiche, A., 1998, Inverting AEM data using a damped eigenparameter method: Exploration Geophysics, 29, 128–132
Inverting AEM data using a damped eigenparameter method:Crossref | GoogleScholarGoogle Scholar |

Christensen, N. B., 2008, Fast approximate 1D inversion of FDHEM data – Bookpurnong, South Australia: CSIRO Exploration and Mining Report Number P2008/1251.

Christensen, N. B., Fitzpatrick, A., and Munday, T., 2010, Fast approximate inversion of frequency-domain electromagnetic data: Near Surface Geophysics, 8, 1–15

Cox, L. H., and Zhdanov, M. S., 2006, Rapid and rigorous 3D inversion of airborne electromagnetic data: presented at SEG International Exposition and 76th Annual Meeting, New Orleans.

Cox, L. H., and Zhdanov, M. S., 2007, Large scale 3D inversion of HEM data using a moving footprint: presented at SEG International Exposition and 77th Annual Meeting, San Antonio.

Cox, L. H., and Zhdanov, M. S., 2008, Advanced computational methods for rapid and rigorous 3D inversion of airborne electromagnetic data: Communications in Computational Physics, 3, 160–179

Combrinck, M., 2008, Calculation of conductivity and depth correction factors for the S-layer differential transform: Exploration Geophysics, 39, 133–138
Calculation of conductivity and depth correction factors for the S-layer differential transform:Crossref | GoogleScholarGoogle Scholar |

Ellis, R. G., 1995, Joint 3D EM inversion: International Symposium on Three-Dimensional Electromagnetics, Expanded Abstracts, 307–323.

Ellis, R. G., 1998, Inversion of airborne electromagnetic data: Exploration Geophysics, 29, 121–127
Inversion of airborne electromagnetic data:Crossref | GoogleScholarGoogle Scholar |

Ellis, R. G., 2002, Electromagnetic inversion using the QMR-FFT fast integral equation method: presented at SEG International Exposition and 72nd Annual Meeting, Salt Lake City.

Farquharson, C. G., Oldenburg, D. W., and Routh, P. S., 2003, Simultaneous 1-D inversion of loop-loop electromagnetic data for magnetic susceptibility and electrical conductivity: Geophysics, 68, 1857–1869
Simultaneous 1-D inversion of loop-loop electromagnetic data for magnetic susceptibility and electrical conductivity:Crossref | GoogleScholarGoogle Scholar |

Fullagar, P. K., and Reid, J. E., 2001, Emax conductivity-depth transformation of airborne TEM data: presented at ASEG 15th Geophysical Conference and Exhibition, Brisbane.

Hohmann, G. W., 1975, Three-dimensional induced polarization and electromagnetic modelling: Geophysics, 40, 309–324
Three-dimensional induced polarization and electromagnetic modelling:Crossref | GoogleScholarGoogle Scholar |

Huang, H., and Fraser, D. C., 2002, Dielectric permittivity and resistivity mapping using high frequency, helicopter-borne EM data: Geophysics, 67, 727–738
Dielectric permittivity and resistivity mapping using high frequency, helicopter-borne EM data:Crossref | GoogleScholarGoogle Scholar |

Hursán, G., and Zhdanov, M. S., 2002, Contraction integral equation method in three-dimensional electromagnetic modelling: Radio Science, 37,
Contraction integral equation method in three-dimensional electromagnetic modelling:Crossref | GoogleScholarGoogle Scholar |

Liu, G., and Becker, A., 1990, Two-dimensional mapping of sea-ice keels with airborne electromagnetic: Geophysics, 55, 239–248
Two-dimensional mapping of sea-ice keels with airborne electromagnetic:Crossref | GoogleScholarGoogle Scholar |

Macnae, J., King, A., Stolz, N., Osmakoff, A., and Blaha, A., 1998, Fast AEM data processing and inversion: Exploration Geophysics, 29, 163–169
Fast AEM data processing and inversion:Crossref | GoogleScholarGoogle Scholar |

Munday, T., Fitzpatrick, A., Doble, R., Berens, V., Hatch, M., and Cahill, K., 2006, The combined use of air, ground and ‘in river’ electromagnetic in defining spatial processes of salinisation across ecologically important floodplain areas – Lower River Murray, SA. In Fitzpatrick, R. W. and Shand, P. (Eds), Proceedings of the CRC LEME Regolith Symposium, 249–255.

Munday, T., Fitzpatrick, A., Reid, J., Berens, V., and Sattel, D., 2007, Frequency and/or time-domain HEM systems for defining floodplain processes linked to the salinisation along the Murray River: presented at ASEG 19th Geophysical Conference and Exhibition, Perth.

Nabighian, M. N., 1979, Quasi-static transient response of a conducting half-space – An approximate representation: Geophysics, 44, 1700–1705
Quasi-static transient response of a conducting half-space – An approximate representation:Crossref | GoogleScholarGoogle Scholar |

Raiche, A. P., 1974, An integral equation approach to three-dimensional modelling: Geophysical Journal of the Royal Astronomical Society, 36, 363–376

Raiche, A., Annetts, D., and Sugeng, F., 2001, EM target response in complex hosts: presented at ASEG 15th Geophysical Conference and Exhibition, Brisbane.

Raiche, A., Wilson, G., and Sugeng, F., 2006, Practical 3D EM inversion for thin sheet structures: presented at Australian Earth Science Convention, Melbourne.

Raiche, A., Sugeng, F., and Wilson, G., 2007, Practical 3D EM inversion – P223F software suite: presented at ASEG 19th Geophysical Conference and Exhibition, Perth.

Reid, J. E., and Macnae, J. C., 1998, Comments on the electromagnetic “smoke ring” concept: Geophysics, 63, 1908–1913
Comments on the electromagnetic “smoke ring” concept:Crossref | GoogleScholarGoogle Scholar |

Reid, J. E., Pfaffling, A., and Vrbancich, J., 2006, Airborne electromagnetic footprints in 1D earths: Geophysics, 71, G63–G72
Airborne electromagnetic footprints in 1D earths:Crossref | GoogleScholarGoogle Scholar |

Sattel, D., 2005, Inverting airborne electromagnetic (AEM) data using Zohdy’s method: Geophysics, 70, G77–G85
Inverting airborne electromagnetic (AEM) data using Zohdy’s method:Crossref | GoogleScholarGoogle Scholar |

Tartaras, E., and Beamish, D., 2005, Laterally constrained inversion of fixed-wing frequency-domain AEM data: presented at 12th European Meeting of Environmental and Near Surface Geophysics, Helsinki.

Tartaras, E., Zhdanov, M. S., Wada, K., Saito, A., and Hara, T., 2000, Fast imaging of TDEM data based on S-inversion: Journal of Applied Geophysics, 43, 15–32
Fast imaging of TDEM data based on S-inversion:Crossref | GoogleScholarGoogle Scholar |

Vallée, M. A., and Smith, R. S., 2009, Inversion of airborne time-domain electromagnetic data to a 1D structure using lateral constraints: Near Surface Geophysics, 7, 63–71

Viezzoli, A., Auken, E., and Munday, T., 2009, Spatially constrained inversion for quasi 3D modelling of airborne electromagnetic data – an application for environmental assessment in the Lower Murray Region of South Australia: Exploration Geophysics, 40, 173–183
Spatially constrained inversion for quasi 3D modelling of airborne electromagnetic data – an application for environmental assessment in the Lower Murray Region of South Australia:Crossref | GoogleScholarGoogle Scholar |

Weidelt, P., 1975, EM induction in three-dimensional structures: Journal of Geophysics, 49, 60–74

Wilson, G. A., Raiche, A. P., and Sugeng, F., 2006, 2.5D inversion of airborne electromagnetic data: Exploration Geophysics, 37, 363–371
2.5D inversion of airborne electromagnetic data:Crossref | GoogleScholarGoogle Scholar |

Wilson, G. A., Cox, L. H., and Zhdanov, M. S., 2010, Practical 3D inversion of entire airborne electromagnetic surveys: Preview, 146, 29–33

Wolfgram, P., and Karlik, G., 1995, Conductivity-depth transform of GEOTEM data: Exploration Geophysics, 26, 179–185
Conductivity-depth transform of GEOTEM data:Crossref | GoogleScholarGoogle Scholar |

Wolfgram, P., and Golden, H., 2001, Airborne EM applied to sulphide nickel – examples and analysis: Exploration Geophysics, 32, 136–140
Airborne EM applied to sulphide nickel – examples and analysis:Crossref | GoogleScholarGoogle Scholar |

Xiong, Z., 1992, Electromagnetic modeling of 3D structures by the method of system iteration using integral equations: Geophysics, 57, 1556–1561
Electromagnetic modeling of 3D structures by the method of system iteration using integral equations:Crossref | GoogleScholarGoogle Scholar |

Zhang, Z., 2003, 3D resistivity mapping of airborne EM data: Geophysics, 68, 1896–1905
3D resistivity mapping of airborne EM data:Crossref | GoogleScholarGoogle Scholar |

Zhdanov, M. S., 2002, Geophysical Inverse Theory and Regularization Problems: Elsevier.

Zhdanov, M. S., 2009, Geophysical Electromagnetic Theory and Methods: Elsevier.

Zhdanov, M. S., and Chernyavskiy, A., 2004, Rapid three-dimensional inversion of multi-transmitter electromagnetic data using the spectral Lanczos decomposition method: Inverse Problems, 20, S233–S256
Rapid three-dimensional inversion of multi-transmitter electromagnetic data using the spectral Lanczos decomposition method:Crossref | GoogleScholarGoogle Scholar |

Zhdanov, M. S., and Tartaras, E., 2002, Three-dimensional inversion of multi-transmitter electromagnetic data based on the localized quasi-linear approximation: Geophysical Journal International, 148, 506–519
Three-dimensional inversion of multi-transmitter electromagnetic data based on the localized quasi-linear approximation:Crossref | GoogleScholarGoogle Scholar |

Zhdanov, M. S., Pavlov, D., and Ellis, R. G., 2002, Localized S-inversion for time-domain electromagnetic data: Geophysics, 67, 1115–1125
Localized S-inversion for time-domain electromagnetic data:Crossref | GoogleScholarGoogle Scholar |