Calibration of the NOMAD-UVIS data

The Ultraviolet and VIsible Spectrometer (UVIS), covering the 200–650 ​nm range, is one of three spectrometers that comprise NOMAD instrument on ExoMars 2016 Trace Gas Orbiter (TGO). UVIS can operate in solar occultation, nadir limb viewing mode was designed to monitor ozone aerosols Martian atmosphere. Here, we describe calibration procedure convert raw data into a calibrated product ready for scientific exploitation. includes CCD offset dark current subtraction, wavelength assignment, noise identification removal, smearing radiance or transmittance conversion. A straylight correction, critical some parts spectral also applied during reduction process, which described more detail two companion papers [Mason et al., 2022; Depiesse In prep] corresponding different independent methods giving consistent results. occultation observations are converted therefore self-calibrating, while measurements require an absolute radiometric calibration. comparison with coincident MRO/MARCI provided as final validation generally shows ±10% agreement radiances measured by both instruments.