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Methane on Mars: new insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration

Liuzzi, Giuliano; Villanueva, Geronimo L.; Mumma, Michael J.; Smith, Michael D.; Daerden, Frank; Ristic, Bojan; Thomas, Ian; Vandaele, Ann Carine; Patel, Manish R.; Lopez-Moreno, José-Juan and Bellucci, Giancarlo (2019). Methane on Mars: new insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration. Icarus, 321 pp. 671–690.

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DOI (Digital Object Identifier) Link: https://doi.org/10.1016/j.icarus.2018.09.021
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Abstract

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, 1σ 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 5 × 5 degrees bins. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.

Item Type: Journal Item
ISSN: 0019-1035
Project Funding Details:
Funded Project NameProject IDFunding Body
Modelling and retrieval of martian dust, ice and ozone from ExoMars NOMAD dataST/P001262/1UKSA UK Space Agency
Science operations for UVIS and CaSSIS on the ExoMars Trace Gas OrbiterST/R005761/1UKSA UK Space Agency
Surface/atmosphere interactions from above and below.ST/S00145X/1UKSA UK Space Agency
Keywords: NOMAD; Methane; Instrumentation; Infrared Spectroscopy; Mars atmosphere
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Related URLs:
Item ID: 56758
Depositing User: ORO Import
Date Deposited: 26 Sep 2018 15:09
Last Modified: 18 Sep 2019 13:48
URI: http://oro.open.ac.uk/id/eprint/56758
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