.. image:: ./_static/emsig-logo.svg
   :width: 400 px
   :align: center
   :alt: emsig logo
   :target: https://emsig.xyz
   :class: dark-light

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========================================
ElectroMagnetic Simulation in Geophysics
========================================

**emsig** are open-source codes to simulate electromagnetic data. Their main
targets are geophysical applications (exploration and monitoring, engineering,
environmental), but they are by no means limited to that. The main codes are
listed on this page. The `emsig GitHub org <https://github.com/emsig/>`_
contains besides the main codes also related publications for reproducibility
purposes and other associated things of interest, such as smaller codes which
were part of publications.


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.. grid:: 1 1 2 2
    :gutter: 2

    .. grid-item-card::
        :img-top: _static/empymod-logo.svg

        3D EM modeller for 1D VTI media
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://empymod.emsig.xyz
            :expand:
            :color: info
            :click-parent:

            empymod.emsig.xyz

        The modeller **empymod** can compute electric or magnetic responses due
        to a 3D electric or magnetic source in a layered-earth model with
        vertical transverse isotropic (VTI) resistivity, VTI electric
        permittivity, and VTI magnetic permeability, from very low frequencies
        (DC) to very high frequencies (GPR). The computation is carried out in
        the wavenumber-frequency domain, and various Hankel- and
        Fourier-transform methods are included to transform the responses into
        the space-frequency and space-time domains.

        ++++++

        .. code:: bash

            pip install empymod

        .. code:: bash

            conda install -c conda-forge empymod

    .. grid-item-card::
        :img-top: _static/emg3d-logo.svg

        Multigrid solver for 3D EM diffusion
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://emg3d.emsig.xyz
            :expand:
            :color: info
            :click-parent:

            emg3d.emsig.xyz

        The modeller **emg3d** is a multigrid solver for 3D EM diffusion with
        tri-axial electrical anisotropy. The matrix-free solver can be used as
        main solver or as preconditioner for Krylov subspace methods, and the
        governing equations are discretized on a staggered Yee grid.

        ++++++

        .. code:: bash

            pip install emg3d

        .. code:: bash

            conda install -c conda-forge emg3d

    .. grid-item-card::
        :img-top: _static/elfe3D-logo.svg

        Modelling with the total electric field approach using finite elements in 3D
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/elfe3D
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/elfe3D

        **elfe3D** is a 3D forward modelling code that can simulate electric
        and magnetic field responses from frequency-domain controlled-source
        electromagnetic geophysical setups. It uses tetrahedral meshes and
        first-order finite-element approximations. In addition, adaptive mesh
        refinement approaches are implemented.

    .. grid-item-card::
        :img-top: _static/EMmod-logo.svg

        The electromagnetic response in a layered vertical transverse isotropic medium
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/EMmod
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/EMmod

        **EMmod**, which stands for electromagnetic modeling, is an algorithm
        to model the full electromagnetic field in a vertical transverse
        isotropic (VTI) layered medium. Although the algorithm was designed for
        frequency-domain marine Controlled Source Electromagnetics (CSEM), it
        can also be used to simulate data for other geophysical exploration
        methods like for example Ground Penetrating Radar (GPR). The algorithm
        computes the EM-field analytically in the wavenumber-frequency domain
        and then carries out a numerical Hankel transformation to get the
        space-frequency domain representation.

    .. grid-item-card::
        :img-top: _static/iEMmod-logo.svg

        Invert frequency-domain electromagnetic data
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/iEMmod
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/iEMmod

        The software **iEMmod** is a non-linear conjugate-gradient algorithm to
        invert frequency-domain electromagnetic data for a layered-Earth model.
        The forward solver used is our open-source layered-Earth
        electromagnetic modeling code EMmod.

    .. grid-item-card::
        :img-top: _static/3Dhom-logo.svg

        Seismoelectromagnetic homogeneous space Green's functions
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/3Dhom
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/3Dhom

        **ElSeisHom3D** stands for computing the Green's functions of
        electromagnetic fields and elastic waves that are coupled in a
        homogeneous porous medium. The fields are the electric field, the
        magnetic field, the particle velocity, the filtration velocity, the
        acoustic pressure in the fluid, and bulk stress. The sources that
        generate these fields are the electric current source, the magnetic
        current source, the force source acting on the bulk, the force source
        acting on the fluid, the acoustic volume injection rate source acting
        on the fluid, and the deformation rate source acting on the bulk. The
        impulse responses that connect the fields to these sources are the
        Green's functions.

    .. grid-item-card::
        :img-top: _static/libdlf-logo.svg

        Library of Digital Linear Filters
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/libdlf
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/libdlf

        **libdlf** is a library for digital linear filters. Codes until now had
        to hard-code their digital linear filters. This has several
        disadvantages. Having a common library that can be used by any code
        base in any language should hopefully widen the adoption of linear
        filters, make their use more reproducible, and might hopefully even
        spark the design of new, hopefully more robust filters or filters for
        new applications.

        ++++++

        .. code:: bash

            pip install libdlf

        .. code:: bash

            conda install -c conda-forge libdlf

    .. grid-item-card::
        :img-top: _static/pyfftlog-logo.svg

        A python version of FFTLog
        ^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://pyfftlog.readthedocs.io
            :expand:
            :color: info
            :click-parent:

            pyfftlog.readthedocs.io

        **pyfftlog** is a python version of the logarithmic FFT code FFTLog.
        FFTLog is a set of fortran subroutines that compute the fast Fourier or
        Hankel (= Fourier-Bessel) transform of a periodic sequence of
        logarithmically spaced points.

        ++++++

        .. code:: bash

            pip install pyfftlog

        .. code:: bash

            conda install -c conda-forge pyfftlog

    .. grid-item-card::
        :img-top: _static/fftlog-logo.svg

        A python wrapper for FFTLog
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^

        .. button-link:: https://github.com/emsig/fftlog
            :expand:
            :color: info
            :click-parent:

            github.com/emsig/fftlog

        **fftlog** is a simple f2py-wrapper for the logarithmic FFT code
        FFTLog. FFTLog is a set of fortran subroutines that compute the fast
        Fourier or Hankel (= Fourier-Bessel) transform of a periodic sequence
        of logarithmically spaced points.

        ++++++

        .. code:: bash

            pip install fftlog

        .. code:: bash

            conda install -c conda-forge fftlog

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:fa:`fas fa-users fa-2x` Contributing & Contact
-----------------------------------------------

**emsig** are community codes, please help to shape their future!

.. grid:: 1
    :gutter: 2

    .. grid-item-card::

        :fa:`code fa-2x`
        `Submit bugs, fix typos, contribute code, and so much more!
        <https://github.com/emsig>`_

    .. grid-item-card::

        :fa:`fa-regular fa-comments fa-2x`
        Join the **#emsig**-channel on the `SWUNG Chat
        <https://softwareunderground.org/mattermost>`_.

    .. grid-item-card::

        :fa:`fa-regular fa-envelope fa-2x`
        If you prefer personal email you can contact me through
        my website `werthmuller.org. <https://werthmuller.org/contact/>`_

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Related ecosystem
=================

**emsig** and its codes are part of a bigger, fast growing, open-source **EM &
Potential Geo-Exploration Python Ecosystem** (make a PR or get in touch to add
your library):

.. raw:: html

   <p style="line-height:10em">

   <a href=https://pygimli.org><img src="https://www.pygimli.org/_static/gimli_logo.svg" style="max-height: 2cm;"></a>

   <a href=https://simpeg.xyz><img src="https://raw.github.com/simpeg/simpeg/master/docs/images/simpeg-logo.png" style="max-height: 2.5cm;"></a>

   <a style="margin:1em" href=https://petgem.bsc.es><img src="https://github.com/ocastilloreyes/petgem/raw/master/doc/source/_static/figures/petgem_logo.png" style="max-height: 3cm;"></a>

   <a href=https://custem.readthedocs.io><img src="https://custem.readthedocs.io/en/latest/_static/custEMlogo.png" style="max-height: 1.5cm;"></a>

   <a href=https://docs.pyvista.org><img src="https://docs.pyvista.org/_static/pyvista_logo.png" style="max-height: 2.5cm;"></a>

   <a style="margin:1em" href=https://www.fatiando.org><img src="https://raw.githubusercontent.com/fatiando/logo/main/logos/fatiando-logo-background.png" style="max-height: 3cm;"></a>

   <a href=https://www.gempy.org><img src="https://raw.github.com/cgre-aachen/gempy/master/docs/source/_static/logos/gempy.png" style="max-height: 2.5cm;"></a>

   <a style="margin:1em" href=https://github.com/softwareunderground/subsurface><img src="https://raw.github.com/softwareunderground/subsurface/main/docs/source/_static/logos/subsurface.png" style="max-height: 3cm;"></a>

   <a href=https://hkex.gitlab.io/resipy><img src="https://hkex.gitlab.io/resipy/_static/logo.png" style="max-height: 3cm;"></a>

   <a href=https://hkex.gitlab.io/emagpy><img src="https://hkex.gitlab.io/emagpy/_static/logo.png" style="max-height: 3cm;"></a>

   <a href=https://emsig.xyz><img src="https://emsig.xyz/_static/emsig-logo.svg" style="max-height: 2cm;"></a>

   <a href=https://mtpy-v2.readthedocs.io><img src="https://mtpy-v2.readthedocs.io/en/latest/_static/mtpy_logo_01.png" style="max-height: 2cm;"></a>

   </p>

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.. dropdown:: About the name and logo of emsig

    The name **emsig** is an abbreviation in English and a pun in German.

    It stands primarily as abbreviation for ElectroMagnetic Simulation in
    Geophysics. However, **emsig** is also a German adjective, meaning
    *hard-working* or *diligent*. Surely, our codes make our computers work
    hard!

    Finally, moving to the logo, the **sig**-ending can be seen as the short
    form of **sigma**, the symbol generally used for conductivity in
    geophysics, one of the elementary properties in electromagnetic modelling.
    The «s» in the logo of **emsig** is denoted by «ς», a variation of «σ»
    (sigma) in the Greek alphabet.

    The symbol itself represents the perpendicularity of electric and magnetic
    fields.

    .. image:: ./_static/emsig-logo.svg
        :class: dark-light