Calibration data
----------------

Calibration data for magnetotelluric recordings comes in many different flavours. Resistics aim to provide a unified experience when handling calibration data. This means that upon reading a calibration data file, a :class:`~resistics.calibrate.data.CalibrationData` object is returned, which has the calibration data in units:

- Magnitude in mV/nT (with static gain applied)
- Phase in radians

.. note::

    Any static gain is automatically added to the calibration data upon read. If the static gain is not desired, please set this to 1 in the calibration file.

The package tries to support the major formats, though this becomes harder when they are binary formatted. Currently, there are four supported calibration formats. These are:

.. toctree::
    :maxdepth: 2
    :titlesonly:

    calibration/metronix-calibration.rst
    calibration/rsp-calibration.rst
    calibration/rspx-calibration.rst
    calibration/ascii-calibration.rst

.. note::

    Currently, resistics only supports calibration of data channels based on:
    
    - sensor type
    - sensor serial number
    - chopper information (low frequency or high frequency recording mode) 
    
    This will cover the calibration of magnetic channels. However, there is presently no easy way of doing a recording instrument calibration. Depending on the need for this feature, it can be implemented. Please get in touch if this is something that is required by visiting the :doc:`Contact <../contact>` page.


.. important 

    Within the resistics project environment, calibration files must be stored in the calData folder to be automatically picked up. Naming conventions for the calibration files are dependent on the format and are described in more detail in the individual sections for the different formats.

Extending calibration data
~~~~~~~~~~~~~~~~~~~~~~~~~~

Often times, calibration data does not cover the whole range of evaluation frequencies to be processed. In this case, the calibration data needs to be extended. By default, resistics will extend calibration data by simply extrapolating out the edge points. In some cases, it is better for the extension of calibration data to be performed outside of resistics. In this case, calibration extension can be switched off as a configuration option. For more details, see the :doc:`Configuration <../features/configuration>` section.

.. warning::

    Extension of calibration happens in the units of the raw calibration data rather than in mV/nT. This means for Metronix calibration format, where the magnitude values are given in V/(nT*Hz), the extrapolation will happen in this unit.

Viewing calibration data
~~~~~~~~~~~~~~~~~~~~~~~~

As calibration is another major point of pain and failure in the processing of magnetotelluric data, resistics includes tools for viewing calibration data. This is good practice, to ensure that calibration files are being read in appropriately. See the sections covering each format for examples of viewing calibration data.