DESMEX - the method

AEM/LOTEM \(\Rightarrow\) semi-airborne EM: Turair, FlairTEM, GREATEM, … GATEM

New semi-airborne method

  • improved sensors and data processing (frequency domain)
  • new modelling and inversion

The DESMEX technology

  • combine advantages of ground Tx with airborne Rx coverage

Semi-airborne scheme (Becken et al. 2020)

DESMEX workflow (Becken et al. 2020)
  • fourier transform of \(b(t)\) & \(e(t)\)
  • data: transfer functions \(\mathfrak B(\vec{r},\omega)=B(\vec{r},\omega)/I(\omega)\) \(\mathfrak E(\vec{r},\omega)=E(\vec{r},\omega)/I(\omega)\)

Data processing

Estimation of transfer functions
  • MT-like (Fourier coefficient)
  • spectral & spatial binning
  • robust estimators
  • new approaches for natural source (Thiede et al. 2024), (Thiede and Becken 2025)
  • improved IMU sensors
  • use of AI algorithms for EM and IMU time series (Posters Kotowski, Wendel, Steinhoff)

Sensors & platforms

Modelling (Rochlitz et al. 2019)

Arbitrary topography, transmitter layout, suburface geometry

Inversion (Rochlitz et al. 2023)

Helicopter surveys

DESMEX I

DESMEX II

DESMEX-Real

  • Lautenthal
  • Schulenberg
  • Clausthal

Schleiz - validation (Steuer et al. 2020)

2D results based on Smirnova et al. (2019), Mörbe et al. (2020) & Oppermann and Günther (2018)

Schleiz 3D result (Rochlitz et al. 2023)

Kropfmühl graphite exploration (Mörbe et al. 2024)

Survey design

Result without (left) and with (right) IP effects

The DESMEX-Real (& -II) surveys

Campaigns 2020-24

  • 2020: 4 flights
  • 2021: 4 flights
  • 2022: 14 flights
  • 2023: 10 flights
  • 2024: 10 flights
  • 39 patches (3rep)
  • total area 400km²
  • 35x5000x8x3x2 = 5 Mio data

Large-scale inversion approaches

Cluster inversion result
  • inversion on single and clustered patches

Large-scale model through cluster re-grouping (Nazari et al. 2024)

Results and geological interpretation

Horizontal slice at 150 asl

UAV-based semi-airborne EM

UAV-based sAEM systems: a) MagArrow OPM, b) sensor (Stoll et al. 2019), c) Münster bird

Mineral exploration with UAV

Hope mine inversion result (Rochlitz et al. 2025)

Poderosa inversion result (Rochlitz et al. 2025)

UAV graphite deposit Kropfmühl

3D inversion result (Mörbe et al. subm.)

Higher frequency - sensitivity

Sensitivity for Bx (left) & Bz (right), 1 (bottom) and 16 (top) kHz (Günther et al. 2021)

Groundwater applications

Groundwater salinization (Abickhafe)

2D inversion (Günther et al. 2021)

Saltwater uprise (Giesen)

3D inversion (Günther et al. 2022)
  • aquifer salinity of Blanco-Arrue et al. (2024)
  • groundwater exploration in southern Africa (talk Mörbe et al.)

Open questions

  • understanding (passive) infrastructure effects (Poster Treppke et al.)

Measured & modelled infrastructure effects at 90 Hz corrected using the secondary source approach

Open questions

  • understanding (passive and active) infrastructure effects
  • automate tedious data processing and
  • current clamps & time shift problems
  • using data in the vicinity of the transmitter
  • data-driven frequency-dependent error models
  • fully exploiting existent data (whole Schleiz data, E-fields, whole Harz)
  • fully hierarchical and memory-saving large-scale inversion
  • upscaling with regional methods (AFMAG, MT)

The way forward

Inverse problem size (Jacobian) in literature (Weiss et al. 2025)

Improvements

  • numerical solvers
  • from frequency to time domain
  • improved sensors
  • broader scope

Numerical solvers and preconditioners

\[\curl \mu^{-1}\curl\vb E + \imath\omega\sigma\vb E = -\imath\omega\vb j_s\]

\[(\vb K + \imath \vb M)\vb u =\vb b\]

\[\vb K_{ij} = <\mu^{-1} \curl v_i, \curl v_j>\]

\[\vb M_{ij} = \omega <\sigma v_i, v_j>\]

Iterative solver with PRESB preconditioner (Weiss et al. 2025)

  • solve \((\vb M + \vb K)\vb g=\vb f_1+\vb f_2\)
  • solve \((\vb M + \vb K)\vb h=\vb f_1 - \vb M \vb g\)

Going time domain

\[ \vb K \vb u(t) + \vb M \pdv{\vb u}{t} = 0 \]

  • methods implemented in custEM

Comparison of Implicit Euler (IE), Fourier transform (FT) and Rational Arnoldi (RA) (Rochlitz et al. 2021)

Performance of RKFIT (Börner and Güttel 2025) compared to RA
  • time-domain measurement and processing

DESMEX-MinD proposal

  • gravity, seismics, magnetics
  • develop Harz geological model
  • geochemistry \(\Rightarrow\) prospectivity
  • model integration by AI methods
  • surveys in ore mountains

Contribution to reproducible research

Thanks and see talks

  • Skibbe&Rochlitz
  • Mörbe et al.
  • Schiffler et al.
  • Börner & Güttel
  • Bayat & al.

and posters

  • Thiede et al.
  • Treppke et al.
  • Steinhoff et al.
  • Rochlitz & Skibbe
  • Blanco Arrue & al.

References

Becken M, Kotowski P O, Schmalzl J, Symons G and Brauch K. 2022. Semi-airborne electromagnetic exploration using a scalar magnetometer suspended below a multicopter. First Break. 40. 37–46
Becken M, Nittinger C G, Smirnova M, Steuer A, Martin T, Petersen H, Meyer U, Mörbe W, Yogeshwar P, Tezkan B, Matzander U, Friedrichs B, Rochlitz R, Günther T, Schiffler M and Stolz R. 2020. DESMEX: A novel system development for semi-airborne electromagnetic exploration. GEOPHYSICS. 1–49
Börner R-U and Güttel S. 2025. Fast parallel transient electromagnetic modelling using a uniform-in-time approximation to the exponential. Geophysical Journal International. 243
Günther T, Ronczka M, Rochlitz R, Kotowski P and Müller-Petke M. 2021. A new drone-based semi-airborne electromagnetic system for mapping saltwater-freshwater interfaces. 1st conference on hydrogeophysics
Günther T, Ronczka M, Rochlitz R and Müller-Petke M. 2022. Using drone-based electromagnetics for 3D imaging of groundwater salinization. 3rd conference on airborne, drone & robotic geophysics
Kotowski P O, Becken M, Rochlitz R, Schmalzl J, Ueding S, Tolksdorf P, Wilhelm A and Symons G. 2025. Semi-airborne electromagnetic exploration of deep sulfide deposits with UAV-towed magnetometers — part 1: Processing and modeling. GEOPHYSICS. 90. WA261–74
Kotowski P O, Becken M, Thiede A, Schmidt V, Schmalzl J, Ueding S and Klingen S. 2022. Evaluation of a semi-airborne electromagnetic survey based on a multicopter aircraft system. Geosciences. 12
Mörbe W, Yogeshwar P, Hoffmann E and Tezkan B. subm. Investigation of a graphitedeposit with drone-borne semi-airborne electromagnetics. Geophysics
Mörbe W, Yogeshwar P, Tezkan B and Hanstein T. 2020. Deep exploration using long-offset transient electromagnetics:interpretation of field data in time and frequency domain. Geophysical Prospecting
Mörbe W, Yogeshwar P, Tezkan B, Kotowski P, Thiede A, Steuer A, Rochlitz R, Günther T, Brauch K and Becken M. 2024. Large-scale 3D inversion of semi-airborne electromagnetic data — topography and induced polarization effects in a graphite exploration scenario. GEOPHYSICS. 89. B339–52
Nazari S, Walther C, Thiede A, Schiffler M, Rochlitz R, Becken M and Günther T. 2024. Large-scale mineral exploration using semi-airborne EM in harz mountains, germany. NSG 2024 5th conference on geophysics for mineral exploration and mining (EAGE)
Oppermann F and Günther T. 2018. A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach. Geoscientific Instrumentation, Methods and Data Systems. 7. 55–66
Rochlitz R, Becken M and Günther T. 2023. Three-dimensional inversion of semi-airborne electromagnetic data with a second-order finite-element forward solver. Geophys. J. Int. 234. 528
Rochlitz R, Günther T, Kotowski P O and Becken M. 2025. Semi-airborne electromagnetic exploration of deep sulfide deposits with UAV-towed magnetometers - part 2: Inversion resolution analysis. GEOPHYSICS. 90. WA307–22
Rochlitz R, Seidel M and Börner R-U. 2021. Evaluation of three approaches for simulating 3-d time-domain electromagnetic data. Geophysical Journal International. 227. 1980–95
Rochlitz R, Skibbe N and Günther T. 2019. custEM: Customizable finite-element simulation of complex controlled-source electromagnetic data. GEOPHYSICS. 84. F17–33
Smirnova M V, Becken M, Nittinger C, Yogeshwar P, Mörbe W, Rochlitz R, Steuer A, Costabel S and Smirnov M Y. 2019. A novel semiairborne frequency-domain controlled-source electromagnetic system: Three-dimensional inversion of semiairborne data from the flight experiment over an ancient mining area near schleiz, germany. GEOPHYSICS. 84. E281–92
Smirnova M, Juhojuntti N, Becken M and Smirnov M. 2020. Exploring kiruna iron ore fields with large-scale, semi-airborne, controlled-source electromagnetics. First Break. 38. 35–40
Steuer A, Smirnova M, Becken M, Schiffler M, Günther T, Rochlitz R, Yogeshwar P, Mörbe W, Siemon B, Costabel S, Preugschat B, Seht M I, Zampa L S and Müller F. 2020. Comparison of novel semi-airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from schleiz, germany. Journal of Applied Geophysics. 182. 104172
Stoll J, Noellenburg R, Kordes T, Becken M, Tezkan B, Yogeshwar P, Bergers R and Matzander U. 2019. Semi-airborne electro-magnetics using a multicopter. Proceedings of the GEM-2019Workshop, xi’an, china.
Stolz R, Schiffler M, Becken M, Thiede A, Schneider M, Chubak G, Marsden P, Bergshjorth A B, Schaefer M and Terblanche O. 2022. SQUIDs for magnetic and electromagnetic methods in mineral exploration. Mineral Economics. 35. 467–94
Thiede A and Becken M. 2025. A self-consistent response function estimator for airborne natural source EM processing. Geophysical Journal International. 243. 573–89
Thiede A, Schiffler M, Junge A and Becken M. 2024. Multivariate processing of airborne natural source electromagnetic data—application to field data from gobabis (namibia). Geophysical Journal International. 238. 573–89
Weiss M, Rochlitz R and Günther T. 2025. Evaluation of an iterative framework for geophysical electromagnetic forward and inverse modelling problems. Geophysical Journal International. 243