Journal of the Earth and Space Physics

Journal of the Earth and Space Physics

Inverse Modeling of Airborne Time-Domain Electromagnetic (ATEM) Data

Document Type : Research Article

Authors
Javad Babaei
Reza Ghanati
Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran.
10.22059/jesphys.2026.412524.1007767
Abstract
Time-domain airborne electromagnetic (ATEM) methods have gained a prominent role in mineral exploration, hydrogeological investigations, and environmental monitoring due to their rapid data acquisition, extensive spatial coverage, and capability to probe considerable depths. Despite these advantages, the quantitative interpretation of ATEM data remains challenging because of the inherent ill-posedness of electromagnetic inversion, the non-uniqueness of recovered models, sensitivity to noise, and the influence of systematic calibration uncertainties. These limitations necessitate careful implementation of forward modeling and inversion strategies, along with appropriate regularization techniques. In this study, the ATEM system response was investigated based on the fundamental principles of electromagnetism and established analytical formulations for one-dimensional (1D) layered-earth models. Both frequency-domain and time-domain representations were examined to provide a comprehensive understanding of the electromagnetic response behavior. Using widely accepted computational tools for forward simulation and inversion, the performance and reliability of these frameworks were evaluated through both synthetic modeling and real-data applications. Forward modeling conducted on synthetic layered-earth scenarios demonstrated that variations in electrical conductivity and layer thickness exert a strong control on the amplitude and temporal decay characteristics of the secondary electromagnetic fields. Specifically, shallow conductive layers generate high-amplitude responses with rapid decay rates, while deeper or more resistive structures produce lower-amplitude signals that persist over longer time intervals. These results highlight the sensitivity of ATEM data to subsurface electrical properties and confirm the theoretical expectations derived from diffusion-based electromagnetic theory. Subsequent inversion of the synthetic datasets showed that the general resistivity structure of the subsurface can be recovered with acceptable accuracy, although fine-scale features may be smoothed due to regularization and limited resolution. The inversion results emphasize the trade-off between data fit and model smoothness, which is a critical aspect of stabilizing ill-posed geophysical problems. In the applied stage, real ATEM data acquired from multiple survey profiles in Australia were analyzed to assess the practical performance of the methodology. The inverted resistivity sections revealed significant geological features, including deep conductive zones, near-surface resistive layers, and structural discontinuities associated with faults and fracture systems. These interpretations are consistent with available geological and geophysical information, demonstrating the reliability and effectiveness of the adopted approach. Overall, the findings of this study indicate that the careful application of standard forward modeling and inversion algorithms enables realistic estimation of subsurface geo-electrical structures from ATEM data. The method proves to be highly valuable for mineral exploration, groundwater assessment, and environmental studies. To further enhance the robustness and resolution of ATEM interpretations, future work should focus on incorporating prior geological constraints, integrating complementary geophysical datasets such as magnetic and seismic data, and advancing toward three-dimensional inversion frameworks. Additionally, systematic uncertainty quantification using stochastic or resampling techniques is recommended to better assess model reliability and reduce ambiguity in interpretation.
Keywords
Airborne Time-Domain Electromagnetic (ATEM)
forward modeling
inversion
subsurface resistivity
Subjects
Ackman, T. E. (2003). An introduction to the use of airborne technologies for watershed characterization in mined areas. Mine Water and the Environment, 22, 62–68.
Auken, E., Boesen, T., & Christiansen, A.V., (2017). A review of airborne electromagnetic methods with Focus on Geotechnical and Hydrological applications from 2007 to 2017. Advanced Geophycis. 58, 47–93.
Auken, E., Westergaard, J., Christiansen, A.V., & Sorensen, K. (2007), Processing and inversion of SkyTEM data for high resolution hydrogeophysical surveys: 19th International Geophysical Conference and Exhibition, Australian Society of Exploration Geophysicists, Extended Abstracts.
Blatter, D., Key, K., Ray, A., Foley, N., Tulaczyk, S., & Auken, E., (2018). Trans-dimensional Bayesian inversion of airborne transient EM data from Taylor Glacier, Antarctica. Geophysical Journal International, 214(3), 1919–1936
Brodie, R.C., & Richardson, M., (2015). Open Source Software for 1D Airborne Electromagnetic Inversion. In: 24th International Geophysical Conference and Exhibition (Perth), Extended Abstracts, pp. 1–3.
Chave, A. D. (1983). Numerical integration of related Hankel transforms by quadrature and continued fraction expansion. Geophysics, 48(12), 1671–1686.
Constable, S. C., Parker, R. L., & Constable, C. G., (1987). Occam’s inversion: a practical algorithm for generating smooth models from electromagnetic sounding data. Geophysics 52 (3), 289–300.
Christiansen, A. V., Auken, E., & Sørensen, K. I. (2006). The transient electromagnetic method. In R. Kirsch (Ed.), Groundwater Geophysics: A Tool for Hydrogeology (pp. 179–224). Springer.
Cunion, E. (2009). Comparison of ground TEM and VTEM responses over kimberlites in the Kalahari of Botswana. In 20th Geophysical Conference and Exhibition, ASEG, Extended Abstracts.
Farquharson, C. G. (2000). Background for Program EM1DFM. University of British Columbia, Geophysical Inversion Facility.
Farquharson, C. G., Oldenburg, D. W., & Routh, P. S. (2003). Simultaneous 1-D inversion of loop–loop electromagnetic data for magnetic susceptibility and electrical conductivity. Geophysics, 68(6), 1857–1869.
Fitterman, D. V., & Yin, C. (2004). Effect of bird maneuver on frequency-domain helicopter EM response. Geophysics, 69(5), 1203–1215.
Gamey, T. J., Doll, W. E., Duffy, A., & Millhouse, D. S. (2000). Evaluation of improved airborne techniques for detection of UXO. In Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) (pp. 57–66). Environmental and Engineering Geophysical Society.
Ghosh, D. P. (1971). The application of linear filter theory to the direct interpretation of geoelectrical resistivity sounding. Geophysical Prospecting, 19(2), 192–217.
Guptasarma, D., & Singh, B. (1997). New digital linear filters for Hankel J0 and J1 transforms. Geophysical Prospecting, 45(5), 745–762.
Hansen, T. M., (2020). Efficient probabilistic inversion using the rejection sampler-exemplified on airborne EM data. Geophysical Journal International, 224, 543–557.
Heagy, L. J., Kang, S., Cockett, R., & Oldenburg, D. W., (2020). Open-source software for simulations and inversions of airborne electromagnetic data, Exploration Geophysics, 51(1), 38–44.
Huang, H., & Fraser, D. C. (2001). The resistivity of layered earth from airborne electromagnetic measurements. Geophysics, 66(2), 508–520.
Koefoed, O. (1972). A note on the linear filter method of interpreting resistivity sounding data: Geophysical Prospecting, 20(2), p403-405.
Konishi, N. (1998). Landslide surveys in Tertiary soft-rock areas using HEM. Exploration Geophysics, 29, 234–239.
Lawrie, K.C., Munday, T.J., Dent, D.L., Gibson, D.L., Brodie, R.C., Wilford, J., Reilly, N.S., Chan, R.N., & Baker, P. (2000a). A geological systems approach to understanding the processes involved in land and water salinisation; the Gilmore project area, central-west New South Wales: AGSO Research Newsletter, 32, p13-15.
Lawrie, K.C., Munday, T.J., Gibson, D.L., Chan, R., Brodie, R., Wilford, J., Reilly, N., & Foster, K. (2000b), Mapping porphyry Au-Cu and epithermal Au mineral systems under complex regolith cover, Lachlan fold belt, N.S.W: 15th Australian geological convention. Sydney, N.S.W. Australia, Geological Society of Australia Sydney N.S.W. Australia.
Lawson, C.L., & Hanson, D.J. (1974), Solving Least Squares Problems: Englewood Cliffs.
Lin, J., Jian, C., & Zhang, Y., (2021). Rapid and high-resolution detection of urban underground space using transient electromagnetic method. IEEE Trans. Industr. Inform. 18, 2622–2631.
Lines, L., R. & Treitel, S. (1984). Tutorial: A review of least-squares inversion and its application to geophysical problems: Geophysical Prospecting, 32, 159-186.
Macnae, J. C. (1995). Esoteric and mundane geophysics for diamondiferous pipe exploration. Exploration Geophysics, 26(2–3), 131–137.
Marquardt, D., W. (1963). An algorithm for least squares estimation of non-linear parameters. Journal of the Society of Industrial and Applied Mathematics, 11, 431-441.
Menke, W. 1989, Geophysical data analysis : discrete inverse theory, Academic Press.
Minsley, B. J., Foks, N. L., & Bedrosian, P. A., (2021). Quantifying model structural uncertainty using airborne electromagnetic data. Geophysical Journal International, 224, 590–607.
Oldenburg, D. W., & Li, Y. (1999). Estimating depth of investigation in DC resistivity and IP surveys. Geophysics, 64(2), 403–416.
Palacky, G.J., & West, G.F. (1991). Airborne electromagnetic methods, in Nabighian, M.N. ed., Electromagnetic methods in applied geophysics, Volume 2, Application, Parts A and B; Investigations in Geophysics No. 3: Society of Exploration Geophysicists, p811-879.  
Parker, R. L. (1994). Geophysical inverse theory. Princeton University Press.
Raiche, A. (1998). Modelling the time-domain response of AEM systems. Exploration Geophysics, 29, no. 1&2, p103-106.
Reid, J. E., Vrbancich, J., & Worby, A. P. (2003). A comparison of shipborne and airborne electromagnetic methods for Antarctic sea-ice thickness measurements. Exploration Geophysics, 34, 46–50.
Smith, R., Fountain, D., & Allard, M. (2003). The MEGATEM fixed-wing transient EM system applied to mineral exploration: A discovery case history. First Break, 21(7), 73–77.
Sorensen, C., Fisher, A., & Costelloe, M. (2009). Airborne electromagnetic survey results from the Paterson Province, WA: 20th Geophysical Conference and Exhibition, Australian Society of Exploration Geophysicists, Extended Abstracts.
Wait, J. R. (1982). Geo-Electromagnetism. Academic Press.
Ward, S. H., & Hohmann, G. W. (1988). Electromagnetic theory for geophysical applications. In M. N. Nabighian (Ed.), Electromagnetic Methods in Applied Geophysics (Vol. 1: Theory, pp. 131–311). Society of Exploration Geophysicists.
Witherly, K., & Irvine, R. (2006). The VTEM heli time-domain EM system—Four case studies. In 18th Geophysical Conference and Exhibition, ASEG, Extended Abstracts.
Wolfgram, P., & Vrbancich, J. (2006). Layered-earth inversions of AEM bathymetry data incorporating aircraft attitude and bird offset—A Torres Strait case study. In 17th Geophysical Conference and Exhibition, ASEG, Extended Abstracts.
Xiaodong, Y., Xi, Y., Xuben, W., Congde, L., Peng, Z., & Bin, C, (2022). A novel trans-dimensional Bayesian inversion strategy for airborne time-domain electromagnetic data. Journal of Applied Geophysics, 199, 104586.
Yin, C. C., Zhu, J., Qiu, C. K., & Cai, J., (2018). Spatially constrained inversion for airborne EM data using quasi-3D models. Chinese Journal of Geophysics, 61(6), 2537–2547
Zong-Hui, G., Chang-Chun, Y., Yan-Fu, Q., Bo, Zh., Xiu-Yan, R., &Yong-Chao, L., (2018). Transdimensional Bayesian inversion of time domain airborne EM data. Applied Geophysics, 15(2), 318–331.
Journal of the Earth and Space Physics
Volume 52, Issue 2
online publication date: 5 September 2026
Summer 2026
Pages 271-291