End-of-mission calibration of the Cassini Imaging Science Subsystem

Abstract

We provide an end-of-mission update to the in-flight calibration of the Imaging Science Subsystem cameras on the Cassini spacecraft, resolving discrepancies in our previous analyses from 2004 to 2010, incorporating data through the end of the mission, adding a correction for the weak but measurable camera sensitivity decline over time, and providing new transmission values for polarizing filters. In the new analysis, we add full-disk photometry of Jupiter and the Saturnian icy satellites Rhea, Dione and Enceladus to the previous measurements, which had consisted primarily of standard star targets, while the stellar photometry is updated to include a correction for light lost to the extended wings of the instrumental point spread function. The resulting absolute flux corrections differ considerably from those previously reported, shifting measured radiance by close to 10% in most broadband filters, and bringing agreement between star and satellite targets to within 3%. We also detail improvements to the narrow-angle camera flat field correction, and provide updates to the filter-by-filter point spread functions, hot pixel correction, and polarizer calibration. For the latter, we present new measurements of Titan’s polarization from near-UV to near-IR, including three methane bands and nearby spectral windows.