Summary: Ground-based observations are usually limited to spectral windows between the strong absorptions of species in the terrestrial atmosphere. When observing solar system- and exo- planetary atmospheres these same atomic and molecular absorptions are of interest. To get precise determinations of molecular abundances in planetary observations from ground-based telescopes, the effects of the Earth’s atmosphere need to be accurately removed. This task is complicated by variations in the concentrations of telluric absorbing species. The strong absorptions by carbon dioxide and water are among the most important and problematic.
What we as astronomers seek to eliminate is of great interest to environmental and atmospheric scientists. The concentrations of telluric water vapour, carbon dioxide and methane are the subject of emerging greenhouse gas monitoring programs.
We have developed code to work with the highly developed and well-regarded VSTAR radiative transfer atmospheric fitting software to attack these problems. ATMOF – ATMOspheric Fitting – makes use of VSTAR models of the terrestrial atmosphere as plug-in modules; it uses the Levenberg-Marquardt method to vary the mixing ratios of molecules in the models to fit calibration data (either standard star or solar observations) and determine the state of the atmosphere. The model is then used to remove telluric absorptions from observations of planets – producing a pure spectrum.
Here we report on our progress in developing ATMOF for these dual purposes.