Stray light correction for measurements of comet 67P acquired by Rosetta's Visible and InfraRed Thermal Imaging...

Rosetta's Visible and InfraRed Thermal Imaging Spectrometer, IR Mapping channel (VIRTIS-M-IR), acquired many hyperspectral images of comet 67P/Churyumov-Gerasimenko that can be used to derive physical and compositional surface properties of the comet's nucleus. As in any optical system, stray light emerges from, e.g., roughness, as well as particulate and molecular contaminations of the optical elements. It redistributes radiation from well-illuminated to darker regions in the instrument's field of view. We develop and apply a stray light correction based on the deconvolution with respect to a stray light kernel that we were able to reconstruct from inflight measurements. We found that the stray light emergence can be explained best when a spectral component is included in addition to the spatial redistribution of source radiation. Typically, the maximum radiances increase on the order of 5% because of the stray light correction. The stray light corrected cubes enable the derivation of nucleus surface properties from consistently calibrated radiance measurements, as well as the distinction of stray light from dust coma signals or signals from shadowed regions.