The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1 sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5x5 degrees bins.Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate. 2013). The Earth-facing hemisphere can be mapped with long-slit spectrometers, providing a snapshot in time/season of the targeted trace gas (and CO2), examples include CH4, H2O and HDO (Villanueva et al. 2015), and O3 through (its photolysis product) O2(a 1 ∆g) (Novak et al., 2002) Recent measurement campaigns have been conducted using the iSHELL spectrograph at the NASA InfraRed Telescope Facility observatory in Hawaii. Despite the very high quality of iSHELL (with a resolving power ~70000), ground-based observations cannot provide a truly comprehensive, global and continuous temporal picture of the abundances, global distributions and possible local release of individual trace gases on Mars. Ground-based observations are reserved to restricted time periods, since they require enough spectral Doppler shift between Mars and Earth to avoid severe blanketing of the Mars gaseous signatures by terrestrial counterparts, and the requested observing interval is not always awarded. Furthermore, the mapping capabilities are very limited in Mars polar regions, and in general are usually limited to a single hemisphere of the planet. Despite t...