Inversion of remote sensing measurements of Middle and Upper Planetary Atmospheres under non-equilibrium conditions

This thesis treats the inversion of remote sensing measurements (infrared spectra) of middle and upper planetary atmospheres, through bayesian inversion strategy. The first part of the work regards the study of the middle and upper atmosphere of Titan, through inversion of VIMS measurements, a spectrometer aboard the Cassini mission. VIMS measured emission from CO, CH4, HCN and C2H2 in the 3-5 μm region, in conditions of non-Local Thermodynamic Equilibrium (non-LTE). The CO concentration in the upper stratosphere and mesosphere of Titan has been determined from the inversion of a set of day-side VIMS limb measurements around 4.7 μm. This represents the first measurement of the CO VMR (Volume Mixing Ratio) profile between 200 and 500 km on Titan. The latitudinal and seasonal variations in the distribution of CH4, HCN and C2H2 in the upper atmosphere of Titan between 500 and 1000 km were studied from VIMS measurements in the 2.8-3.5 μm region. The significance of the preliminary results is discussed with regard to the small coverage at the polar latitudes and the observed correlation between the retrieved CH4 VMR and SZA at high altitudes. A bias observed in the results of the inversion of CH4 brought to the development of SpectRobot (SR), a new code for radiative transfer modeling and inversion of atmospheric quantities, that considers the full 3D geometry of the problem. The second part of this work regards the study of the first measurements acquired by JIRAM, an infrared imager/spectrometer aboard the Juno mission to Jupiter. In the 3-4 μm region JIRAM measures the emission from H3+, which is a great tracer for the auroral phenomena, since it is produced by the precipitation of energetic electrons. Maps of the average retrieved H3+ column density, emission temperature and CH4 column density have been produced for the two auroral regions.