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Rapid approximate inversion of airborne TEM

Citation

Fullagar, PK and Pears, GA and Reid, JE and Schaa, R, Rapid approximate inversion of airborne TEM, Exploration Geophysics, 46, (1) pp. 112-117. ISSN 0812-3985 (2015) [Refereed Article]

Copyright Statement

Copyright 2015 ASEG

DOI: doi:10.1071/EG14046

Abstract

Rapid interpretation of large airborne transient electromagnetic (ATEM) datasets is highly desirable for timely decision-making in exploration. Full solution 3D inversion of entire airborne electromagnetic (AEM) surveys is often still not feasible on current day PCs. Therefore, two algorithms to perform rapid approximate 3D interpretation of AEM have been developed. The loss of rigour may be of little consequence if the objective of the AEM survey is regional reconnaissance. Data coverage is often quasi-2D rather than truly 3D in such cases, belying the need for ‘exact’ 3D inversion.

Incorporation of geological constraints reduces the non-uniqueness of 3D AEM inversion. Integrated interpretation can be achieved most readily when inversion is applied to a geological model, attributed with lithology as well as conductivity. Geological models also offer several practical advantages over pure property models during inversion. In particular, they permit adjustment of geological boundaries. In addition, optimal conductivities can be determined for homogeneous units. Both algorithms described here can operate on geological models; however, they can also perform ‘unconstrained’ inversion if the geological context is unknown.

VPem1D performs 1D inversion at each ATEM data location above a 3D model. Interpretation of cover thickness is a natural application; this is illustrated via application to Spectrem data from central Australia. VPem3D performs 3D inversion on time-integrated (resistive limit) data. Conversion to resistive limits delivers a massive increase in speed since the TEM inverse problem reduces to a quasi-magnetic problem. The time evolution of the decay is lost during the conversion, but the information can be largely recovered by constructing a starting model from conductivity depth images (CDIs) or 1D inversions combined with geological constraints if available. The efficacy of the approach is demonstrated on Spectrem data from Brazil.

Both separately and in combination, these programs provide new options to exploration and mining companies for rapid interpretation of ATEM surveys.

Item Details

Item Type:Refereed Article
Keywords:airborne EM, geological constraints, inversion, resistive limit, time domain
Research Division:Earth Sciences
Research Group:Geophysics
Research Field:Electrical and Electromagnetic Methods in Geophysics
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Mineral Exploration not elsewhere classified
Author:Schaa, R (Dr Ralf Schaa)
ID Code:105806
Year Published:2015
Web of Science® Times Cited:3
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2016-01-14
Last Modified:2016-09-06
Downloads:0

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