eradiate.radprops.absorption.compute_sigma_a(ds, wl=<Quantity(550.0, 'nanometer')>, p=<Quantity(101325.0, 'pascal')>, t=<Quantity(288.15, 'kelvin')>, n=None, fill_values=None, methods=None)[source]#

Compute monochromatic absorption coefficient at given wavelength, pressure and temperature values.

  • ds (Dataset) – Absorption cross section data set.

  • wl (quantity) – Wavelength [nm].

  • p (quantity) – Pressure [Pa].


    If p, t and n are arrays, their lengths must be the same.

  • t (quantity) – Temperature [K].


    If the coordinate t is not in the input dataset ds, the interpolation on temperature is not performed.

  • n (quantity) – Number density [m^-3].


    If n is None, the values of t and p are then used only to compute the corresponding number density.

  • fill_values (dict, optional) – Mapping of coordinates (in ["w", "pt"]) and fill values (either None or float). If not None, out of bounds values are assigned the fill value during interpolation along the wavelength or pressure and temperature coordinates. If None, out of bounds values will trigger the raise of a ValueError. Only one fill value can be provided for both pressure and temperature coordinates.

  • methods (dict, optional) – Mapping of coordinates (in ["w", "pt"]) and interpolation methods. Default interpolation method is linear. Only one interpolation method can be specified for both pressure and temperature coordinates.


quantity – Absorption coefficient values.


ValueError – When wavelength, pressure, or temperature values are out of the range of the data set and the corresponding fill value in fill_values is None.


The values of the absorption cross section at the desired wavelength, pressure and temperature values, \(\sigma_{a\lambda} (p, T)\), are obtained by interpolating the input absorption cross section data set along the corresponding dimensions.


The absorption coefficient is given by:

\[k_{a\lambda} = n \, \sigma_{a\lambda} (p, T)\]


  • \(k_{a\lambda}\) is the absorption coefficient [\(L^{-1}\)],

  • \(\lambda\) is the wavelength [\(L\)],

  • \(n\) is the number density [\(L^{-3}\)],

  • \(\sigma_a\) is the absorption cross section [\(L^2\)],

  • \(p\) is the pressure [\(ML^{-1}T^{-2}\)] and

  • \(t\) is the temperature [\(\Theta\)].