Unbiased estimations of atmosphere vortices: the Saturn's storm view by Cassini VIMS-V as a case study

A method to assess appearance and size of meteorological dynamical structures elliptically shaped on a horizontal plane, without any bias connected to human operator evaluations, has been applied to the giant vortex embedded in the 2010 Saturn's Great Storm, observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini. The method consists in a two-dimensional, elliptical Gaussian fitting procedure applied to the radiance distribution on the spectral images. The Full Width Half Maxima (FWHMs) of the 2D Gaussian are assumed as the axes and their crossing point as the center of the vortex. The fit parameters, calculated in pixel coordinates, have been converted in Geographical Coordinate System (GCS) through the association between pixels and geographical coordinates by SPICE; then the appropriate distances have been computed. The analysis cover the period from May 2011 up to January 2012. The time evolution of shape and size of the vortex has been determined in correspondence of the stronger methane band at 890 nm. A drift estimation has been also calculated in relationship to the vortex center.