ESO in-kind Projekt

Ground-based astronomical observations suffer from emission and absorption processes in the atmosphere, which deteriorate the quality of the obtained data. In particular, at wavelengths longer than 2 − 2.5 μm, where thermal radiation from molecules in the lower atmosphere dominates, with the help of this disturbing background radiation one can estimate whether scientific observations are feasible at all. For this wavelength regime it is crucial to be able to estimate the intensity of the atmospheric emission in advance. Such a prediction requires good knowledge of the column densities of atmospheric constituents that significantly contribute to the greenhouse effect. The most important molecules are water (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃). In particular, a good knowledge of the water abundance, i.e. air humidity, is essential, since H₂O is the main contributor to the IR atmospheric spectra. Moreover, it is much more variable than the other important species.

The aim of project DR06 is to provide an ESO tool for fitting tropospheric/stratospheric telluric features and for deriving correction functions for the removal of these features from spectra of astronomical targets. This tool will potentially be provided to the ESO community. In its current version, it is able to take into account the actual atmospheric profile (i.e. the variation of pressure, temperature, and relative humidity with altitude) and can adapt the column densities of different atmospheric constituents independently. For most wavelength windows, this allows a model accuracy of better than a few percent and, hence, the derivation of reliable atmospheric parameters. The development of the Common Pipeline Library (CPL) workflows is based on an Interactive Data Language (IDL) prototype code by A. Smette (ESO).

The whole user documentation is given in the ESO document archive as Nr.: VLT–MAN–ESO–19550–5286

complete range 0.3 - 30 µm (click image to enlarge)	zoom to one CRIRES range 3.27 - 3.36 µm (click image to enlarge)	zomm to one VISIR range 9.0 - 10.6µm (click image to enlarge)
Influence of individual molecules as a function of wavelength: this figures shows the relative importance of all molecules at a given wavelength, which exceed more than 5% of the total radiance (in red) or transmission (in blue) - CLICK on the figures to enlarge.