Recent observations of Saturn performed by the Cassini probe, orbiting the ringed system since July 2004, show that a giant oval structure has formed in the planet's North hemisphere. The structure has been observed in different hyperspectral images retrieved by the visual channel of the spectrometer VIMS (VIMS-V) on board Cassini, starting from May 2011. The goal of this work is to evaluate the top level of the clouds located over the oval structure observed by VIMS around 35° North latitude, by examining the bottom of the 893 nm methane (CH4) absorption band by means of the VIMS-V hyperspectral images analysis. Methane is indeed the most absorbing gas in Saturn's atmosphere in the wavelength range covered by VIMS-V, that is 350 ÷ 1050 nm. Moreover, the 893 nm absorption band is the strongest in this wavelength range and it allows to sound the highest levels of the atmosphere. A radiative transfer model has been developed to simulate the radiance field on the planet. This model uses the discrete ordinate solver for a plane parallel atmosphere. Besides different configurations of microphysical, optical and geometrical parameters both for clouds and aerosols have been considered. Aerosol parameters must be carefully tuned to obtain the fit between the synthetic and VIMS-V measured spectra. Preliminary results are given, along with possible explanations for the obtained discrepancies.
Cloud Top evaluation of a Cloud-Saturn's giant vortex by Cassini VIMS-V observations.
ML Moriconi;
2012
Abstract
Recent observations of Saturn performed by the Cassini probe, orbiting the ringed system since July 2004, show that a giant oval structure has formed in the planet's North hemisphere. The structure has been observed in different hyperspectral images retrieved by the visual channel of the spectrometer VIMS (VIMS-V) on board Cassini, starting from May 2011. The goal of this work is to evaluate the top level of the clouds located over the oval structure observed by VIMS around 35° North latitude, by examining the bottom of the 893 nm methane (CH4) absorption band by means of the VIMS-V hyperspectral images analysis. Methane is indeed the most absorbing gas in Saturn's atmosphere in the wavelength range covered by VIMS-V, that is 350 ÷ 1050 nm. Moreover, the 893 nm absorption band is the strongest in this wavelength range and it allows to sound the highest levels of the atmosphere. A radiative transfer model has been developed to simulate the radiance field on the planet. This model uses the discrete ordinate solver for a plane parallel atmosphere. Besides different configurations of microphysical, optical and geometrical parameters both for clouds and aerosols have been considered. Aerosol parameters must be carefully tuned to obtain the fit between the synthetic and VIMS-V measured spectra. Preliminary results are given, along with possible explanations for the obtained discrepancies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
