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 VIMS-V, on board Cassini, starting from May 2011. VIMS is a multi-channel imaging spectrometer, able to produce 2D images of the observed target that also contain their spectral information. The instrument consists of an infrared channel (VIMS-IR) ranging from 0.85 to 5.1 mum and a visual channel (VIMS-V) operating in the wavelength range 0.35 - 1.05 mum; the visual channel has a nominal spectral resolution of 7.3 nm and a nominal angular resolution of 500 murad; in this study we will work on the data collected by this last one. We evaluate the top level of the clouds located over the oval structure observed on January 2012 by VIMS around 35° North latitude, by examining the bottom of the 0.89-mum 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. Moreover, the 0.89 mum absorption band is the strongest in this wavelength range and it allows us 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 and considers different configurations of microphysical, optical and geometrical parameters both for clouds and aerosols. These parameters have been tested to fit to the 0.89 mum CH4 absorption band whose depth depends also on the reflection by the highest clouds and/or haze layers. Finally, aerosol parameters must be carefully tuned to obtain the same shape between the synthetic and VIMS-V measured spectra. Vortices have been observed at Saturn since the Voyager missions, but thanks to Cassini we now have the possibility to study their evolution with a better continuity and with high spatial and spectral resolution. The temporal variability for the retrieved cloud-top level is then checked by analyzing two hyperspectral observations imaging the same vortex, recorded on a time lapse of five months. To this extent we'll take advantage of the results obtained in a parallel study (Moriconi et al., 2012) and presented in a second abstract. References M.L. Moriconi, E. D'Aversa, A. Adriani, G.Filacchione: Cassini VIMS-V observations of a giant dynamical structure in the Saturn's northern hemisphere. Abstract submitted to this meeting, 2012.
Cloud-Top evaluation of a Saturn's giant vortex by Cassini VIMS-V observations / Oliva, Fabrizio; A., Adriani; M., Moriconi; E., D'Aversa. - In: EOS. - ISSN 2324-9250. - ELETTRONICO. - (2012). (Intervento presentato al convegno American Geophysical Union Fall Meeting 2012 tenutosi a San Francisco nel 3-7/12/2012).
Cloud-Top evaluation of a Saturn's giant vortex by Cassini VIMS-V observations
OLIVA, FABRIZIO;
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 VIMS-V, on board Cassini, starting from May 2011. VIMS is a multi-channel imaging spectrometer, able to produce 2D images of the observed target that also contain their spectral information. The instrument consists of an infrared channel (VIMS-IR) ranging from 0.85 to 5.1 mum and a visual channel (VIMS-V) operating in the wavelength range 0.35 - 1.05 mum; the visual channel has a nominal spectral resolution of 7.3 nm and a nominal angular resolution of 500 murad; in this study we will work on the data collected by this last one. We evaluate the top level of the clouds located over the oval structure observed on January 2012 by VIMS around 35° North latitude, by examining the bottom of the 0.89-mum 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. Moreover, the 0.89 mum absorption band is the strongest in this wavelength range and it allows us 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 and considers different configurations of microphysical, optical and geometrical parameters both for clouds and aerosols. These parameters have been tested to fit to the 0.89 mum CH4 absorption band whose depth depends also on the reflection by the highest clouds and/or haze layers. Finally, aerosol parameters must be carefully tuned to obtain the same shape between the synthetic and VIMS-V measured spectra. Vortices have been observed at Saturn since the Voyager missions, but thanks to Cassini we now have the possibility to study their evolution with a better continuity and with high spatial and spectral resolution. The temporal variability for the retrieved cloud-top level is then checked by analyzing two hyperspectral observations imaging the same vortex, recorded on a time lapse of five months. To this extent we'll take advantage of the results obtained in a parallel study (Moriconi et al., 2012) and presented in a second abstract. References M.L. Moriconi, E. D'Aversa, A. Adriani, G.Filacchione: Cassini VIMS-V observations of a giant dynamical structure in the Saturn's northern hemisphere. Abstract submitted to this meeting, 2012.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
