radis.lbl.calc moduleΒΆ


Public (front-end) functions to calculate Spectrum with HITRAN / CDSD databanks. Uses the SpectrumFactory class from factory.py, Spectrum from spectrum.py and line survey from line_survey.py

Routine ListingΒΆ


calc_spectrum(wmin=None, wmax=None, wunit=cm - 1, Tgas=None, Tvib=None, Trot=None, pressure=1.01325, molecule=None, isotope='all', mole_fraction=1, path_length=1, databank='hitran', medium='air', wstep=0.01, truncation=50, neighbour_lines=0, cutoff=1e-27, parsum_mode='full summation', optimization='simple', chunksize=None, broadening_method='voigt', overpopulation=None, name=None, save_to='', use_cached=True, mode='cpu', export_lines=False, verbose=True, return_factory=False, **kwargs) Spectrum[source]ΒΆ

Calculate a Spectrum.

Can automatically download databases (HITRAN/HITEMP) or use manually downloaded local databases, under equilibrium or non-equilibrium, with or without overpopulation, using either CPU or GPU.

It is a wrapper to SpectrumFactory class. For advanced used, please refer to the aforementionned class.

  • wmin, wmax (float [\(cm^{-1}\)] or Quantity) –

    wavelength/wavenumber range. If no units are given, use \(cm^{-1}\)

    calc_spectrum(2000, 2300, ... )   # cm-1
    calc_spectrum(4000, 4200, wunit='nm', ...)

    You can use arbitrary units:

    import astropy.units as u
    calc_spectrum(2.5*u.um, 3.0*u.um, ...)
  • wunit ('nm', 'cm-1') – unit for wmin and wmax. Default is "cm-1".

  • Tgas (float [\(K\)]) – Gas temperature. If non equilibrium, is used for \(T_{translational}\). Default 300 K​

  • Tvib, Trot (float [\(K\)]) – Vibrational and rotational temperatures (for non-LTE calculations). If None, they are at equilibrium with Tgas ​.

  • pressure (float [\(bar\)] or Quantity) –

    partial pressure of gas in bar. Default 1.01325 (1 atm)​. Use arbitrary units:

    import astropy.units as u
    calc_spectrum(..., pressure=20*u.mbar)
  • molecule (int, str, list or None) – molecule id (HITRAN format) or name. For multiple molecules, use a list. The 'isotope', 'mole_fraction', 'databank' and 'overpopulation' parameters must then be dictionaries. If None, the molecule can be infered from the database files being loaded. See the list of supported molecules in MOLECULES_LIST_EQUILIBRIUM and MOLECULES_LIST_NONEQUILIBRIUM. Default None.​

  • isotope (int, list, str of the form '1,2', or 'all', or dict) – isotope id (sorted by relative density: (eg: 1: CO2-626, 2: CO2-636 for CO2). See [HITRAN-2020] documentation for isotope list for all species. If 'all', all isotopes in database are used (this may result in larger computation times!). Default 'all'.

    For multiple molecules, use a dictionary with molecule names as keys

    isotope={'CO2':'1,2' ,  'CO':'1,2,3' }​
  • mole_fraction (float or dict) – database species mole fraction. Default 1.

    For multiple molecules, use a dictionary with molecule names as keys

    mole_fraction={'CO2': 0.8, 'CO':0.2}​
  • path_length (float [\(cm\)] or Quantity) –

    slab size. Default 1 cm​. Use arbitrary units:

    import astropy.units as u
    calc_spectrum(..., path_length=1000*u.km)
  • databank (str or dict) – can be either: - 'hitran', to fetch the latest HITRAN version

    through fetch_hitran() (download full database with [HAPI]) or fetch_astroquery() (download only the required range). To use one mode or the other, use

    databank=('hitran', 'full')     # download and cache full database, all isotopes
    databank=('hitran', 'range')    # download and cache required range, required isoope
    • 'hitemp', to fetch the latest HITEMP version through fetch_hitemp(). Downloads all lines and all isotopes.

    • 'exomol', to fetch the latest ExoMol database through fetch_exomol(). To download a specific database use (more info in fetch_exomol)

      databank=('exomol', 'EBJT')   # 'EBJT' is a specific ExoMol database name
    • 'geisa', to fetch the GEISA 2020 database through fetch_geisa(). Downloads all lines and all isotopes.

    • the name of a a valid database file, in which case the format is inferred. For instance, '.par' is recognized as hitran/hitemp format. Accepts wildcards '*' to select multiple files

    • the name of a spectral database registered in your ~/radis.json configuration file


    Default 'hitran'. See DatabankLoader for more information on line databases, and DBFORMAT for your ~/radis.json file format.

    For multiple molecules, use a dictionary with molecule names as keys:

    databank='hitran'     # automatic download (or 'hitemp')
    databank='PATH/TO/05_HITEMP2019.par'    # path to a file
    databank='*CO2*.par' #to get all the files that have CO2 in their names (case insensitive)
    databank='HITEMP-2019-CO'   # user-defined database in Configuration file
    databank = {'CO2' : 'PATH/TO/05_HITEMP2019.par', 'CO' : 'hitran'}  # for multiple molecules
Other Parameters
  • medium ('air', 'vacuum') – propagating medium when giving inputs with 'wavenum_min', 'wavenum_max'. Does not change anything when giving inputs in wavenumber. Default ``’air’``​

  • wstep (float (\(cm^{-1}\)) or 'auto') – Resolution of wavenumber grid. Default 0.01 cm-1. If 'auto', it is ensured that there are slightly more or less than radis.config ['GRIDPOINTS_PER_LINEWIDTH_WARN_THRESHOLD'] points for each linewidth.


    wstep = β€˜auto’ is optimized for performances while ensuring accuracy, but is still experimental in 0.9.30. Feedback welcome!

  • truncation (float (\(cm^{-1}\))) – Half-width over which to compute the lineshape, i.e. lines are truncated on each side after truncation (\(cm^{-1}\)) from the line center. If None, use no truncation (lineshapes spread on the full spectral range). Default is 300 \(cm^{-1}\)


    Large values (> 50) can induce a performance drop (computation of lineshape typically scale as \(~truncation ^2\) ). The default 300 was chosen to maintain a good accuracy, and still exhibit the sub-Lorentzian behavior of most lines far (few hundreds \(cm^{-1}\)) from the line center.

  • neighbour_lines (float (\(cm^{-1}\))) – The calculated spectral range is increased (by neighbour_lines cm-1 on each side) to take into account overlaps from out-of-range lines. Default is 0 \(cm^{-1}\).​

  • cutoff (float (~ unit of Linestrength: \(cm^{-1}/(molec.cm^{-2})\))) – discard linestrengths that are lower that this, to reduce calculation times. 1e-27 is what is generally used to generate line databases such as CDSD. If 0, no cutoff. Default 1e-27 .

  • parsum_mode (β€˜full summation’, β€˜tabulation’) – how to compute partition functions, at nonequilibrium or when partition function are not already tabulated. 'full summation' : sums over all (potentially millions) of rovibrational levels. 'tabulation' : builds an on-the-fly tabulation of rovibrational levels (500 - 4000x faster and usually accurate within 0.1%). Default 'full summation'


    parsum_mode= β€˜tabulation’ is new in 0.9.30, and makes nonequilibrium calculations of small spectra extremelly fast. Will become the default after 0.9.31.

  • optimization ("simple", "min-RMS", None) – If either "simple" or "min-RMS" LDM optimization for lineshape calculation is used:

    • "min-RMS" : weights optimized by analytical minimization of the RMS-error (See: [Spectral-Synthesis-Algorithm])

    • "simple" : weights equal to their relative position in the grid

    If using the LDM optimization, broadening method is automatically set to 'fft'. If None, no lineshape interpolation is performed and the lineshape of all lines is calculated. Refer to [Spectral-Synthesis-Algorithm] for more explanation on the LDM method for lineshape interpolation. Default "simple".

  • overpopulation (dict) – dictionary of overpopulation compared to the given vibrational temperature. Default None. Example:

    overpopulation = {'CO2' : {'(00`0`0)->(00`0`1)': 2.5,
                               '(00`0`1)->(00`0`2)': 1,
                               '(01`1`0)->(01`1`1)': 1,
                               '(01`1`1)->(01`1`2)': 1 }
  • export_lines (boolean) – if True, saves details of all calculated lines in Spectrum. This is necessary to later use line_survey(), but can take some space. Default False.

  • name (str) – name of the output Spectrum. If None, a unique ID is generated.

  • save_to (str) – save to a spec file which contains absorption & emission features, all calculation parameters, and can be opened with load_spec(). File can be reloaded and exported to text formats afterwards, see savetxt(). If file already exists, replace.

  • use_cached (boolean) – use cached files for line database and energy database. Default True.​

  • verbose (boolean, or int) – If False, stays quiet. If True, tells what is going on. If >=2, gives more detailed messages (for instance, details of calculation times). Default True.​

  • mode ('cpu', 'gpu', 'emulated_gpu') – if set to 'cpu', computes the spectra purely on the CPU. if set to 'gpu', offloads the calculations of lineshape and broadening steps to the GPU making use of parallel computations to speed up the process. Default 'cpu'. Note that mode='gpu' requires CUDA compatible hardware to execute. For more information on how to setup your system to run GPU-accelerated methods using CUDA and Cython, check GPU Spectrum Calculation on RADIS To try the GPU code without an actual GPU, you can use mode='emulated_gpu'. This will run the GPU equivalent code on the CPU.

  • return_factory (bool) – if True, return the SpectrumFactory that computes the spectrum. Useful to access computational parameters, the line database, or to start batch-computations from a first spectrum calculation. Ex:

    s, sf = calc_spectrum(..., return_factory=True)
    sf.df1  # see the lines calculated
    sf.eq_spectrum(...)  #  new calculation without reloading the database
  • **kwargs (other inputs forwarded to SpectrumFactory) – For instance: warnings. See SpectrumFactory documentation for more details on input.


  • Spectrum – Output spectrum:

    • Use the get() method to retrieve a spectral quantity ('radiance', 'radiance_noslit', 'absorbance', etc…)

    • Or the plot() method to plot it directly.

    • See 1 to get an overview of all Spectrum methods

  • :py:class:`~radis.lbl.factory.SpectrumFactory` (if using return_factory=True) – if multiple molecules, a dictionary of factories is returned



RADIS doc: Spectrum how to?

​.. [2] RADIS GPU support: GPU Calculations on RADIS ​


Calculate a CO spectrum from the HITRAN database:

from radis import calc_spectrum
s = calc_spectrum(1900, 2300,         # cm-1
                  pressure=1.01325,   # bar
                  databank='hitran',  # or 'hitemp'
s.apply_slit(0.5, 'nm')

This example uses the apply_slit() and plot() methods. See also line_survey():


Calculate a CO2 spectrum from the CDSD-4000 database:

s = calc_spectrum(2200, 2400,   # cm-1
                  pressure=0.1,  # bar


This example uses the eq_spectrum_gpu() method to calculate the spectrum on the GPU. The databank points to the CDSD-4000 databank that has been pre-processed and stored in numpy.npy format. ​ Refer to the online Examples for more cases, and to the Spectrum page for details on post-processing methods.

For more details on how to use the GPU method and process the database, refer to the examples linked above and the documentation on GPU support for RADIS. ​ .. minigallery:: radis.calc_spectrum


cite: RADIS is built on the shoulders of many state-of-the-art packages and databases. If using RADIS to compute spectra, make sure you cite all of them, for proper reproducibility and acknowledgement of the work ! See How to cite? and the cite() method.

See also