Photometric modelling and VIS-IR albedo maps of Rhea from Cassini-VIMS

Abstract

Photometric correction based on the Shkuratov method is applied to derive visible and infrared albedo maps of Rhea from disc-resolved Cassini VIMS data. Differently from I/F images, albedo maps offer an optimal disentanglement of composition and physical properties of the surface from illumination-viewing effects and to study spectral variations occurring at hemispherical and local scales. A similar methodology has been already applied to Dione's and Tethys's data sets returned by VIMS. Following the same scheme also for Rhea, spectral albedo is derived at 59 wavelengths between 0.35 and 5.047 μm. Equigonal albedo maps are rendered in cylindrical projection with a 0.5$^\circ \, \times$ 0.5° angular resolution in latitude and longitude, corresponding to a maximum spatial resolution of 6.7 km bin-1. Apart from albedo, 0.35-0.55 and 0.55-0.95 μm spectral slopes and the water ice 1.5-2.0 μm band depth maps are computed from photometric-corrected data with the specific scope to investigate the leading-trailing hemisphere colour-albedo dichotomy and to constrain spectral properties above different morphological units including fresh craters (Inktomi) and bright tectonics features (Wakonda-Avaiki Chasmata).