.. _sec-user_guide-data-absorption:

Absorption data
===============

Absorption datasets tabulate the volume absorption coefficient of a gas mixture
against spectral index, mixture's components' volume fraction, air pressure
and air temperature.

For monochromatic absorption datasets, the spectral index consists
of a radiation wavelength or radiation wavenumber coordinate.

For CKD absorption datasets, the spectral index consists of two coordinates:

* the center of the spectral band (in wavelength or wavenumber space)
* the absorption coefficient cumulative probability, or :math:`g`-point.

Data access
-----------

Distributed absorption datasets are available from the
`Eradiate store <http://eradiate.eu/data/store/>`_.

.. note::

   You can also plug in your own datasets, provided they comply with the
   below specifications.

Specifications
--------------

Monochromatic
~~~~~~~~~~~~~

Monochromatic absorption coefficient datasets include one data variable:

* volume absorption coefficient (``sigma_a``),

and at least four :term:`dimension coordinates <dimension coordinate>`:

* radiation wavelength or radiation wavenumber (``w``),
* gas mixture mole fractions (``x_M`` where ``M`` is the molecule formula,
  e.g. ``x_H2O``),
* air pressure (``p``),
* and air temperature (``t``).

CKD
~~~

CKD absorption coefficient datasets include at least two data variables:

* ``sigma_a [x_M, p, t, w, g]`` : volume absorption coefficient
* ``wbounds [wbv, w]`` : band spectral bounds

one optional data variable:

* ``error [w, ng]`` : relative error on atmosphere band-averaged transmittance,

at least five :term:`dimension coordinates <dimension coordinate>`:

* ``w`` : radiation wavelength or radiation wavenumber of the band center,
* ``wbv`` : band wavelength bounds,
* ``g`` : quadrature :math:`g`-point,
* ``x_M`` (where ``M`` is the molecule formula, e.g. ``x_H2O``, ``x_CO2``): gas
  mixture mole fractions (1 to :math:`N_M` coordinates where :math:`N_M` is the
  number of molecules in the mixture),
* ``p`` : air pressure,
* ``t`` : and air temperature,

and, if the data variable ``error`` is present:

* ``ng`` : number of quadrature :math:`g`-point.


Available datasets
------------------

Monochromatic datasets
~~~~~~~~~~~~~~~~~~~~~~

.. list-table:: Available monochromatic datasets
   :widths: 25 25 25 25
   :header-rows: 1

   * - Codename
     - Spectral range
     - Sampling resolution
     - Online data store path
   * - ``gecko``
     - [250, 3125] nm
     - 0.01 :math:`\rm{cm}^{-1}` in [250, 300] :math:`\cup` [600, 3125] nm,
       0.1 :math:`\rm{cm}^{-1}` in [300, 600] nm
     - ``spectra/absorption/mono/gecko/``
   * - ``komodo``
     - [250, 3125] nm
     - 1 :math:`\rm{cm}^{-1}`
     - ``spectra/absorption/mono/komodo/``

CKD datasets
~~~~~~~~~~~~

.. list-table:: Available CKD datasets
   :widths: 25 25 25 25
   :header-rows: 1

   * - Codename
     - Spectral range
     - Band widths
     - Online data store path
   * - ``monotropa``
     - [250, 3125] nm
     - 100 :math:`\rm{cm}^{-1}`
     - ``spectra/absorption/ckd/monotropa/``
   * - ``panellus``
     - [250, 3125] nm
     - 1 nm
     - ``spectra/absorption/ckd/panellus/``
   * - ``mycena``
     - [250, 3120] nm
     - 10 nm
     - ``spectra/absorption/ckd/mycena/``