BGR Bundesanstalt für Geowissenschaften und Rohstoffe

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Model coupling HEM1D+

Making 1D resistivity subsurface models more realistic

Our problem: 1D or 3D? Which model is needed?

Airborne electromagnetic data sets are able to reveal information about the spatial conductivity distribution in the subsurface of large survey areas. As the footprint of helicopter-borne electromagnetic (HEM) measurements is rather small (some 100 m), many conductivity structures having small lateral variations only are close to uniform settings. Therefore, stitched together 1D inversion models are widely used to approximately display the 3D conductivity distribution. Laterally strongly varying conductivity structures (anomalies), however, require 3D modelling. An accurate 3D inversion of the HEM data of an entire survey area is often neither feasible nor necessary.

SP2 structureSP2 structure Source: BGR

Our solution: Both models are needed! They just must be in the right place!

HEM1D+ aims to develop methods enhancing the inversion of HEM data. In particular, a program package will be created that coordinates all tasks related to data import/export, data inversion, model coupling and model import/export. Important sub-goals are

  • joint inversion of different data sets (together with SP1: Aero-Ground-Joint-Inversion),
  • integration of a priori data in HEM 1D inversion,
  • evaluation of the resulting conductivity distribution with respect to 3D effects,
  • extraction of anomalous data sets for 3D inversion, and
  • self consistent combination of 1D and 3D models.

The quality of the HEM inversion results at single sites can be enhanced using additional data and a priori constraints. In addition, a method will be developed that connects the large-scale HEM data with rather local ground geophysical, geological or hydrogeological data sets. Laterally strongly varying conductivity structures (anomalies) will be selected and classified using a search algorithm to be developed that browses the HEM 1D inversion models of an entire survey area. The anomalous data sets will be forwarded to the project partners for 3D modelling (SP3: 3D inversion of HEM data). The resulting 3D models will then be re-integrated into a quasi 1D environment and the combined 1D/3D unambiguous conductivity models will be forwarded to the project partners (SP5: Model development and validation of results) for crosschecking with hydro-geological and geological models.

Contact 1:

Dr. Bernhard Siemon
Phone: +49(0)511-643-3488
Fax: +49(0)511-643-3662

Contact 2:

Dr. Ralph-Uwe Börner
Phone: +49(0)3731-392724
Fax: +49(0)3731-392636


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