1. EM1DFM package overview

1.1. Description

EM1DFM is a Fortran-based, multi-platform program library for carrying out the one-dimensional inversion of frequency-domain, small loop, electromagnetic data acquired to determine the spatial variation of the electrical conductivity and/or magnetic susceptibility of the subsurface. The name “EM1DFM” derives from: electromagnetics (“EM”), one-dimensional models (“1D”), frequency-domain observations (“F”), and magnetic (dipole) sources and receivers (“M”).

The acquired data are measurements of the magnetic field due to electric currents and magnetization induced in the subsurface by a time-varying current in a transmitter loop. Information about how the conductivity and susceptibility vary with depth is obtained by making measurements for different frequencies of the transmitter current, and for different separations, heights and orientations of the transmitters and receivers. Different soundings provide information about the lateral variation in the subsurface. A sounding is a distinct collection of FEM measurements (transmitters, receivers and frequencies) which are used to recover a corresponding 1D layered Earth model. On the figure below, we see two examples. On the left, two soundings (e.g. two separate sets of measurements) are collected at the same location; in this case, the inversion should recover the same model. On the right, we see the use of separate soundings to map lateral variation.

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Fig. 1.1 Two distinct groupings of transmitters and receivers (soundings) at the same location (left). Different soundings used to map lateral variation in the Earth (right). Click to enlarge.

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Fig. 1.2 Layered 1D model describing the Earth for each sounding.

For any sounding location, the mathematical representation that EM1DFM uses to model the Earth varies only with depth. In particular, the representation comprises many uniform, horizontal layers, and it is the conductivity and/or susceptibility within each layer that is computed. Four options are available: just the conductivity in each layer can be constructed, or just the susceptibility (constrained to be positive) in each layer, or both the conductivity and susceptibility with the positivity constraint on the susceptibility, or both the conductivity and susceptibility without the positivity constraint. For a complete mathematical treatment of the forward and inversion problem, see Background Theory.

The initial research underlying this program library was funded principally by the “IMAGE” consortium, of which the following companies were participants: AGIP, Anglo American, Billiton, Cominco, Falconbridge, INCO, MIM, Muskox Minerals, Newmont, Placer Dome and Rio Tinto, and from the Natural Sciences and Engineering Research Council of Canada (NSERC).

1.2. Program library content

This package consists of two programs:

  • EM1DFM: carries out the inversion of small loop, frequency-domain EM data assuming a layered Earth model

  • EM1DFMFWD: a stand-alone program for forward modeling the frequency-domain response assuming a layered Earth model

1.3. Licensing

A constrained educational version of the program is available with the IAG package (please visit UBC-GIF website for details). The educational version is fully functional so that users can learn how to carry out effective and efficient 1D inversions of electromagnetic data. However, RESEARCH OR COMMERCIAL USE IS NOT POSSIBLE because the educational version only allows a limited number of data and model cells.

Licensing for an unconstrained academic version is available - see the Licensing policy document.

NOTE: All academic licenses will be time-limited to one year. You can re-apply after that time. This ensures that everyone is using the most recent versions of codes.

Licensing for commercial use is managed by third party distributors. Details are in the Licensing policy document.

1.4. Installing

There is no automatic installer currently available for the . Please follow the following steps in order to use the software:

  1. Extract all files provided from the given zip-based archive and place them all together in a new folder such as

  2. Add this directory as new path to your environment variables.

Two additional notes about installation:

  • Do not store anything in the “bin” directory other than executable applications and Graphical User Interface applications (GUIs).

  • A Message Pass Interface (MPI) version is available for Linux upon and the installation instructions will accompany the code.