Publicly Available Derived Datasets and Tools for Working with Calibrated Spectra from NOMAD on the ExoMars Trace Gas Orbiter

The science phase of the ExoMars Trace Gas Orbiter (TGO) mission began on 21^st April 2018, and since then the NOMAD suite of 3 spectrometers [1] has acquired around 100 million spectra, primarily of the Martian atmosphere and surface. These cover ultraviolet-visible and infrared wavelengths with different observation geometries. The 3 spectrometers are:

1) Solar Occultation (SO): 2.2-4.3 µm (2,300-4,600 cm^-1), spectral resolution 0.1-0.23 cm^-1 [2].

2) Limb, Nadir and Occultation (LNO): 2.2-3.8 µm (2,600-4,600 cm^-1), spectral resolution 0.15-0.28 cm^-1 [2], operating primarily in nadir viewing mode.

3) Ultraviolet-Visible (UVIS): 200-650 nm (15,000-50,000 cm^-1), spectral resolution 1.2-1.7 nm [3], operating in solar occultation, nadir and limb viewing modes.

 

Together, the spectrometers are able to map the vertical distributions and/or column densities (where appropriate) of many properties and constituents of the Martian atmosphere, including H₂O [4] and HDO [5], CO [6], O₃ [7], HCl [8], dust/aerosol particle size [9], CO₂ and H₂O clouds [10], CO₂ temperature and pressure [11], dayglow [12] and nightglow [13] emissions, surface ice/frost [14], plus the reflectance properties of Phobos and Deimos [15]. Also, stringent detection limits can be placed on other gases that have not yet been detected, e.g. CH₄ [16].

 

Calibrated NOMAD spectra and derived climatologies are available to the scientific community in multiple sources, for example: the ESA Planetary Science Archive, Europlanet’s VESPA portal, and many online authors’ repositories. Likewise, modelling tools (for example the NASA Goddard Planetary Spectrum Generator), calibration routines, observation planning information and nadir footprints exist online, are available in journal articles, or can be found on the NOMAD website at nomad.aeronomie.be.

 

Work is ongoing to consolidate all the available datasets and tools, including python code to find and plot online datasets, forward-model the SO and LNO spectrometers, and to understand the instrument and associated uncertainties, which we will describe here. Also, documentation regarding recent calibration improvements will be highlighted and made available online for the community.

 

References

[1] Vandaele, A.C., et al; NOMAD, an integrated suite of three spectrometers for the ExoMars Trace Gas mission: technical description, science objectives and expected performance. (2018) Space Sc. Rev. 214, 80. https://doi.org/10.1007/s11214-018-0517-2

[2] Liuzzi G., et al; Methane on Mars: New insights into the sensitivity of CH₄ with the NOMAD/ExoMars spectrometer through its first in-flight calibration. (2019) Icarus 321, 671-690. https://doi.org/10.1016/j.icarus.2018.09.021

[3] Willame, Y., et al; Calibration of the NOMAD-UVIS data. (2022) Planet. Space Sci., 218, 105504. https://doi.org/10.1016/j.pss.2022.105504

[4] Hendrick, F., et al; New Climatology of Martian Water Vapor Column Abundance Derived from NOMAD LNO Nadir Observations Over Martian Years 34–38. (2026) J. Geophys. Res. Planets. https://doi.org/10.1029/2025JE009592  

[5] Villanueva, G., et al; The deuterium isotopic ratio of water released from the Martian caps as measured with TGO/NOMAD. (2022) Geophys. Res. Lett., 49(12). https://doi.org/10.1029/2022GL098161

[6] Modak, A., et al; Martian Atmospheric CO Vertical Profiles From NOMAD Observations During the First Year of TGO Operations. (2023) J. Geophys. Res. Planets. https://doi.org/10.1029/2022JE007282

[7] Mason, J. P., et al; Climatology and Diurnal Variation of Ozone Column Abundances for 2.5 Mars Years as Measured by the NOMAD-UVIS Spectrometer. (2024) J. Geophys. Res. Planets. https://doi.org/10.1029/2023JE008270

[8] Aoki S., et al; Annual appearance of hydrogen chloride on Mars and a striking similarity with the water vapor vertical distribution observed by TGO/NOMAD. (2021) Geophys. Res. Letters 48(11). https://doi.org/10.1029/2021gl092506

[9] Flimon, Z., et al; Aerosol Climatology on Mars as Observed by NOMAD UVIS on ExoMars TGO in Journal of Geophysical Research: Planets.  (2025) J. Geophys. Res. Planets. https://doi.org/10.1029/2024JE008303

[10] Liuzzi, G., et al; First Detection and Thermal Characterization of Terminator CO₂ Ice Clouds with ExoMars/NOMAD. (2021) Geophys. Res. Letters 48(2). https://doi.org/10.1029/2021gl095895

[11] Trompet, L., et al; Carbon dioxide retrievals from NOMAD-SO on ESA’s ExoMars Trace Gas Orbiter and temperature profiles retrievals with the hydrostatic equilibrium equation. II. Temperature variabilities in the mesosphere at Mars terminator. (2023) J. Geophys. Res. Planets. https://doi.org/10.1029/2022JE007279

[12] Soret, L., et al; The Martian oxygen green line dayglow: response to solar activity. (2025) Icarus. https://doi.org/10.1016/j.icarus.2025.116707

[13] Gérard, J.-C., et al; Observation of the Mars O2 visible nightglow by the NOMAD spectrometer onboard the Trace Gas Orbiter. (2023) Nature Astron. https://doi.org/10.1038/s41550-023-02104-8

[14] Valantinas, A., et al; Evidence for transient morning water frost deposits on the Tharsis volcanoes of Mars. (2024) Nature Geoscience. https://doi.org/10.1038/s41561-024-01457-7

[15] Mason, J. P., et al; Ultraviolet and Visible Reflectance Spectra of Phobos and Deimos as Measured by the ExoMars-TGO/NOMAD-UVIS Spectrometer. (2023) J. Geophys. Res. Planets. https://doi.org/10.1029/2023JE008002

[16] Knutsen, E.W., et al; Comprehensive Investigation of Mars Methane and Organics with ExoMars/NOMAD. (2021) Icarus 257. https://doi.org/10.1016/j.icarus.2020.114266