PFS on Mars Express: preparing the analysis of infrared spectra to be measured by the Planetary Fourier Spectrometer

A radiative transfer simulation and retrieval technique (RRT) is described that will be applied to derive atmospheric and surface properties of Mars from measured infrared signatures recorded by the Planetary Fourier Spectrometer (PFS) onboard the Mars Express mission in 2003. The RRT considers absorption, emission and multiple scattering of thermal and solar radiation by molecular (CO2, H2O, CO) and particulate (palagonite, montmorillonite) species. Precalculated sets of absorption cross-sections which are based on quasi-monochromatic line-by-line calculations are used to predict molecular transmission functions at 2.0 cm−1 spectral resolution in a layered atmosphere. Synthetic infrared spectra have been calculated in the 200–8000 cm−1 wavenumber range (1.25–50 μm) for a variety of atmospheric models and surface conditions. The influence of multiple aerosol scattering on the spectra is investigated on the basis of a successive approximation technique. Numerical results are compared with the spherical harmonics discrete ordinate method. Different retrieval procedures and results of a simultaneous retrieval of vertical temperature profiles and aerosol optical depths as well as surface temperature, pressure and reflectance are discussed. Real measurements performed by the IRIS instrument onboard Mariner 9 are also examined.