High Resolution Spectra
en cours ...
|The data-exchange project described hereafter was initiated in the frame of
It is widely inspired from the LXcat
plasma data-exchange project. It can also be partly compared to the gas mixture spectra
on the web section of the HITRAN
project, as well as the cross section
page of the ExoMol
- ANR 07 BLAN 127 03 ``Exoclimat''
- RTRA ITAAC STAE/2008/PS/002 ``Impact du Trafic Aérien sur l'Atmosphère et le Climat''
- ERC ??
- autres ??
Our objective is to archive high-resolution absorption spectra of molecular gases and provide softwares for computation of effective parameters such as emissivities, k-distributions, or parameters of narrow band average transmissivities and wide band models.
Three steps are followed by radiative transfer physicists when they need high-resolution absorption-spectra of gas-mixtures at given temperatures and pressures (assuming a state of equilibrium), throughout given frequency intervals (commonly as wide as the whole infrared plus visible plus ultraviolet, including hundreds of milions of absorption line centers) :
- Step 1 - selecting a molecular transition databank ;
- Step 2 - making physical assumptions as far as line shapes and collision induced continum are concerned ;
- Step 3 - making numerical choices in the process of constructing the spectrum (frequency discretisation, line selection) and accessing it from radiative transfer codes (data management, interpolation).
Molecular transition databanks (Step 1) are already quite exaustive and accurate and are being continuously refined by an active and well structured community. The HITRAN
project is undenialbly the most illustrative of these structuration efforts.
But as soon as the considered thermodynamic conditions or the considered distances are outside the range typical of either the terrestrial atmosphere or the most common combustion devices, the question of modeling line shapes and collision induced continuum is widely open. Each group of radiative transfer physicists makes then its own physical choices (Step 2) and adjusts its numerical tools accordingly (Step 3). Consequently, until dedicated efforts are made collectively by the community of advanced-spectroscopy users (expecting it not from advanced-spectroscopy experts that have other concerns) :
- Intercomparison of radiative transfer analysis is difficult (pure photon transport considerations cannot be distinguished from discrepancies in absorption properties at each frequency and each field-location, that are complex to evaluate).
- Referenced high-resolution spectra are lacking for radiative transfer physicists or statistical physicists (that are no advanced spectroscopy experts) in the process of designing and evaluating effective spectral representations (such as statistical narrow-band models or k-distribution statistics).
- Radiative transfer results cannot be checked by referees, prior to publication, or reproduced after publication (the technical details of Step 2 and Step 3 cannot be descriped exaustively in the frame of a radiative transfer journal article).
- The exact memory of Step 2 and Step 3 is highly volatile and the significance of radiative transfer conclusions is rapidely lost (it is a very common experience that visiting a research group to learn about the physical and numerical choices made in one of their published work leads to the conclusion that essential ``details'' are no more available).
The above statements are particularly illustrative of the astrophysics-radiation recent history, but the rapidely increasing accuracy requirements of the combustion research community defines strictly identical questions (as far as both heat transfer and optical diagnosis are concerened).
At the present stage we opened a brainstorming session within the STARWest
community and we only uploaded what we called the level-zero databank :
This caricatural databank is meant to serve as a ground-reference for forthcomming uploads, but it can already be used with confidence for numerous engineering applications. It was used in particular within the ITAAC
contrail simulation project.
- Physical assumptions : no collision-induced continuum, all HITRAN 2008 lines included without truncation using the woigt profile, with self-collision broadening and air-collision broadening only.
- Numerical implementation : a one percent accuracy garanty at each frequency when using linear interpolation between successive discrete frequencies.
Each spectrum corresponds to a single gas mixed with pure air, with molar fractions ranging from to , temperatures ranging from to and pressures ranging from to .