Quantifying the effect of primary field modelling on TEMPEST data - The importance of uncertainty

Anders Vest Christiansen; Esben Auken; Yusen Ley-Cooper; Kristoffer Andersen

doi:10.1071/ASEG2016ab251

25th International Conference and Exhibition – Interpreting the Past, Discovering the Future

ISSN: 2202-0586
E-ISSN:

oa Quantifying the effect of primary field modelling on TEMPEST data - The importance of uncertainty
Authors Anders Vest Christiansen^a, Esben Auken^b, Yusen Ley-Cooper^c and Kristoffer Andersen^d
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^a HydrogeophysicsGroup,. Aarhus University, C.F.Møllers Alle 4, 8000, Aarhus, , Denmark, [email protected] ^b HydrogeophysicsGroup, Aarhus Universsity, . C.F.Møllers Alle 4, 8000, Aarhus, , Denmark, [email protected] ^c Mineral Resources, CSIRO, Bentley, , WA, 6102, , Australia, [email protected] ^d HydrogeophysicsGroup, Aarhus University, C.F.Møllers Alle 4, 8000, Aarhus, , Denmark, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2016, Issue 25th International Conference and Exhibition – Interpreting the Past, Discovering the Future, Dec 2016, p. 1 - 5
DOI: https://doi.org/10.1071/ASEG2016ab251
- Published online: 01 Dec 2016

Abstract

The TEMEPST system is used widely for large-scale mapping. It is a fixed-wing time-domain system with the transmitter strung around the aircraft and the receiver coils towed in a bird behind and below the aircraft. The TEMPEST data are special in the sense that the data are presented as B-field, 100 % duty cycle data. In this process the system self-response is removed, which means that one needs to compute and reinstate the primary field that was removed to accurately model the measured data.

In this paper we show that it is crucial to assign uncertainty to the reinstating of the primary field because it can be several orders of magnitude larger than the secondary field especially over resistive grounds and at late times. To quantify the effect of the uncertainty we have produced a number of inversions of a line in the Capricorn survey where we have added different levels of uncertainty when reinstating the primary field. The results have all been produced with the Aarhus Workbench which uses the AarhusInv algorithm and compared with results from the GA-LEI algorithm.

We show that reinstating the primary field into the forward calculations is necessary for accurate modelling of TEMPEST responses. Though, to achieve realistic and fitting inversion models (particularly over resistive ground when less signal is measured) it is crucial to allow for a small uncertainty on the primary field when this is reinstated to the forward response. This balances the inversion and allows for misfits in the range of the assumed data noise, which is not possible for the resistive areas without the assumed noise on the primary.

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References

Auken, E., Christiansen, A. V., Jacobsen, L., and Serensen, K. I., 2008, A resolution study of buried valleys using laterally constrained inversion of TEM data: J. Appl. Geophys., 65, 10-20.
Auken, E., Viezzoli, A., and Christiansen, A. V., 2009, A Single Software For Processing, Inversion, And Presentation Of Aem Data Of Different Systems: The Aarhus Workbench ASEG, Adelaide.
Auken, E., Christiansen, A. V., Fiandaca, G., Schamper, C., Behroozmand, A. A., Binley, A., Nielsen, E., Efferse, F., Christensen, N. B., Serensen, K. I., Foged, N., and Vignoli, G., 2015, An overview of a highly versatile forward and stable inverse algorithm for airborne, ground-based and borehole electromagnetic and electric data: Explor. Geophys., 2015, 223-235.
Christiansen, A. V., Auken, E., and Viezzoli, A., 2011, Quantification of modeling errors in airborne TEM caused by inaccurate system description: Geophysics, 76, F43-F52.
Lane, R., Green, A. G., Golding, C., Owers, M., Pik, P., Plunkett, C., Sattel, D., and Thorn, B., 2000, An example of 3D conductivity mapping using the TEMPEST airborne electromagnetic system: Explor. Geophys., 31, 162-172.
Lane, R., Brodie, R., and Fitzpatrick, A., 2004, Constrained inversion of AEM data from the Lower Balonne area, southern
Leggatt, P. B., Klinkert, P. S. and Hage, T. B., 2000. The Spectrem airborne electromagnetic system-further developments. Geophysics 65(6), 1976-1982.
Ley-Cooper, A. Y., and C. Brodie, R., (2013), Inversion of Spectrem AEM data for conductivity and system geometry: ASEG Extended Abstracts, 2013(1), 1-4.
Ley-Cooper, A. Y., Munday, T., and Ibrahimi, T., (2015), Determining cover variability in the Capricorn Orogen with airborne EM: ASEG Extended Abstracts, 2015(1), 1-6.
Roach, I. C. (ed), 2012. The Frome airborne electromagnetic (AEM) survey, South Australia: implications for energy, minerals and regional geology. Geoscience Australia. Record 2012/40, 296 pp.
Smith, R. S., 2001a. On removing the primary field from fixed-wing time-domain airborne electromagnetic data: some consequences for quantitative modelling, estimating bird position and detecting perfect conductors. Geophysical Prospecting 49, 405-416.
Viezzoli, A., Christiansen, A. V., Auken, E., and Serensen, K. I., 2008, Quasi-3D modeling of airborne TEM data by Spatially Constrained Inversion: Geophysics, 73, F105-F113.

/content/journals/10.1071/ASEG2016ab251

Article Type: Research Article

Keyword(s): Airborne time-domain inversion TEMPEST uncertainty

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oa Quantifying the effect of primary field modelling on TEMPEST data - The importance of uncertainty

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