In-flight radiometric calibration of the ExoMars TGO Colour and Stereo Surface Imaging System

The Colour and Stereo Surface Science Imaging System (CaSSIS) of the ExoMars Trace Gas Orbiter returns on average twenty images per day Martian surface, most them in 3 or 4 colours some stereo. CaSSIS uses a push-frame approach to acquire colour images, with four bandpass filters deposited directly above sensor an imaging cadence synchronized ground track velocity cover imaged area tens small, partially overlapping images. These "framelets" are later map-projected mosaicked build final image. This offers both advantages challenges terms radiometric calibration. While collection dark flatfield frames is considerably enhanced by frequent fast acquisition successive mosaics assembled from adjacent framelets highlight straylight changes bias detector. Both issues have been identified low intensities overall (up few percents), but sufficient generate prominent artefacts We therefore developed methods correct these that now included into calibration pipeline. detail here different steps procedure generation products used for calibration, discuss efficacy corrections. relative uncertainties low, order 0.2 0.1 percents, respectively. uncertainty absolute which quite such instrument. adds estimated about 1 percent error residuals after corrections offsets DNs DNs.