Frequently Asked Questions

Questions Answers
1) Consulting GEISA line transition parameters sub-database, I noticed “-0.9999” value for lower transition level energy. Is it normal ?

  Yes, this value indicates that information about this field was not communicated by the authors and remain unknown. Please see this page for details about all undefined values.

2) For certain entries in the GEISA line transitions sub-database, the quantum identifications of the vibrational and rotational states are missing. Is it normal?

  Yes, this is normal and corresponds to transitions of lines which are presently not completely theoretically described. These kinds of transitions have been kept especially for planetary studies, when they are supposed to be helpful for the understanding of unknown atmospheric composition.

3) What the reference temperature for the « intensity » of a line transition?

  This temperature is 296 K.

4) Why is the line parameters description of the GEISA cross-sections sub-database different from the individual lines one: description by [Temperature/Pressure] couples and not by spectroscopic parameters as described in the GEISA line list format?

  Because of their atmospheric spectroscopic interest, certain compounds corresponding to heavy molecular species such as such as: chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), SF6, and oxides of nitrogen (for example, N2O5) have been introduced in the GEISA cross-sections sub-database. The reason was that it became evident that spectroscopic information on individual spectral lines belonging to this kind of molecules could not be reasonably described in the traditional GEISA individual lines sub-database format (i.e. via, line wavenumber, intensity, halfwidth, etc.). The following approach was adopted to report spectral absorption cross-sections measured at atmospheric conditions:

The absorption cross-sections are determined through the following expression:

σ(ω) = (ln [Ι0 (ω) / Ι (ω)]) / ηι

where ω is a wavenumber(cm-1); σ(&omega) is the absorption cross-section (cm2 molecule-1); Ι0 (ω) and Ι (ω) are the intensities, at the wavenumber &omega, of the incident and transmitted radiation, respectively; Ι is the concentration of the molecules (molecule cm-3) and ι the optical path length (cm), at a temperature T and a pressure P. It is the σ(&omega) value derived from high-resolution experimental data that is cataloged in the GEISA cross-sections sub-database.

It is the σ(&omega) value derived from high-resolution experimental data that is catalogued in the GEISA cross-sections file. It is presented at several (T, P) combinations representing atmospheric layers given in commonly tabulated atmospheric models as well as conditions encountered.

5) Does GEISA allow radiative transfer modeling ?

  GEISA is an interactive spectroscopic database which can be exploited in many fields of research, especially radiative transfer simulations. GEISA is designed to facilitate accurate and fast forward calculations of atmospheric radiative transfer using a line-by-line and (atmospheric) layer-by-layer approach.

6) What is the origin of the spectroscopic data included in GEISA ?

  The spectroscopic data archived in GEISA are directly provided by authors of published papers. These data could be derived experimentally or theoretically. In fact they represent very often the results of associated expertises and efforts in both aspects.

The GEISA website gives a complete description of the origin of each data file with associated references on authors and related articles.


7) What is the format description of a “GEISA line transition parameters sub-database” entry ?

  The detailed format of such an entry is given in this page.

8) What are the N2O isotopologues available in GEISA ?
Molecule Molecule Code Isotopologue Code Formula
N2O 4 446 14N14N16O
447 14N14N17O
448 14N14N18O
456 14N15N16O
546 15N14N16O
458 14N15N18O
548 15N14N18O
556 15N15N16O


The complete list of molecules and isotopologues can be viewed at this page.

9) How much molecules are in GEISA 2011 line transition parameters sub-database?

  The GEISA 2011 sub-database of line transition parameters involves 50 molecules (111 isotopic species) and contains 3,807,997 entries, in the spectral range from 10-6 to 35,877 cm-1.

10) How many option(s) can you use in the interactive interrogation section?

  There are mainly six options (see this page for further explanations) :

  • Information
  • Content analysis
  • Database extract
  • Transition analysis
  • Transition list
  •  Download access

and also the direct download access

11) Is there a downloadable program for reading GEISA 2011 line transition parameters sub-database format.

The format has not been changed since the 2003 version. The same fortran reading program can be use (See GEISA format).

12) When the new version of GEISA will be available ?

The new version is planned for the end of 2019

13) What is the “Graphical Tools” topic on the “database access” menu ?

The “Graphical Tools” topic is a facility to view the contibution of few spectroscopic parameters. There are ” options :

  • Database content
  • Global position
  • Histogram analysis
GEISA has been used as the reference spectroscopic database for the definition of the 4 bands of the CNES/Microcarb. An example of a “global position” visualization of H2O and CO2 isotopologues for the band 3 (strong CO2 band at 1.6 µm) is given here. Microcarb band3 spectral interval