Vertical Structure Modeling of Saturn's Equatorial Region Using High Spectral Resolution Imaging

Abstract

Saturn was observed on 6-11 February 2002 using an Acousto-optic Imaging Spectrometer (AImS) to study Saturn's vertical cloud structure. The 3.67-m Advanced Electro-Optical System telescope at the Maui Space Surveillance Complex was used. The high spectral resolution and wide spectral coverage of AImS (500 - 1000 nm) enabled us to sample the Saturnian atmosphere with high vertical resolution and to derive the wavelength dependence of aerosol properties. The model center-limb profiles were fit to the observed profiles in the equatorial region. Adopting four different cloud models with three aerosol phase functions, we varied up to nine free parameters to seek the best solution. The results of the simultaneous fits to nine different profiles around the 890-nm and 727-nm methane bands suggest that : 1) a cloud model having higher aerosol density in the lower troposphere (0.15 - 1.5 bar) is favorable, 2) the tropospheric cloud extends into the stratosphere, 3) the wavelength dependence of the upper cloud optical thickness indicates that the average aerosol size is larger than 0.7 - 0.8 micron, 4) the average aerosol size of the upper tropospheric cloud increases with depth from about 0.15 micron to between 0.7--0.8 and 1.5 micron, 5) the aerosol properties in February 2002 are similar to those observed during the 1990 equatorial disturbance.