NOMAD, an Integrated Suite of Three Spectrometers for the ExoMars Trace Gas Mission: Technical Description, Science Objectives and Expected Performance

Abstract

The NOMAD ("Nadir and Occultation for MArs Discovery") spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the comThis paper is dedicated to the memory of M. Allen, V. Formisano, and J. McConnell. position of Mars' atmosphere, with a particular focus on trace gases, clouds and dust. The detection sensitivity for trace gases is considerably improved compared to previous Mars missions, compliant with the science objectives of the TGO mission. This will allow for a major leap in our knowledge and understanding of the Martian atmospheric composition and the related physical and chemical processes. The instrument is a combination of three spectrometers, covering a spectral range from the UV to the mid-IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and explain the technical principles of the three spectrometers. We also discuss the expected performance of the instrument in terms of spatial and temporal coverage and detection sensitivity.

Martian Water Ice Clouds During the 2018 Global Dust Storm as Observed by the ACS‐MIR Channel Onboard the Trace Gas Orbiter

“…The ExoMars Trace Gas Orbiter (TGO), ESA‐Roscosmos Atmospheric Chemistry Suite (ACS), and Nadir and Occultation for MArs Discovery (NOMAD) instruments started their science operation phase in March 2018 (Korablev et al, , ; Vandaele et al, , ), before the MY 34 GDS. The ACS Mid‐InfraRed (MIR) channel is a crossed‐dispersion echelle spectrometer dedicated to solar occultation (hereafter, “SO”): each observation covers a 300‐nm wide spectral interval selected between 2.3 and 4.2 m. This interval is set by rotating the spectrometer secondary grating (i.e., the diffraction order separation) to align the interval of interest with the detector.…”

“…Thirteen different positions can be employed to completely sample the full accessible spectral range of the instrument. With the 2‐hr orbital period of TGO and the performing of SO in the mid‐infrared, ACS and NOMAD provide a totally new and huge data set of vertical profiles of the atmospheric extinction (Korablev et al, ; Vandaele et al, ). We are using the ACS‐MIR channel to study the extinction properties of the Martian airborne particles in the 3‐ m spectral region, which possesses a distinct diagnostic capability to identify the O‐H stretching signature, whether it is due to water ice absorption or bound water in dust.…”

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

“…These results are then used in the second part, where we perform an analysis of the instrument capabilities in detecting CH4 in solar occultation geometry, at different levels of aerosol opacity, and in Nadir geometry for different illumination conditions and surface albedos, accounting also for aerosol opacity. These problems are recently assessed in Vandaele et al, 2018 for other gases together with CH4 and its different isotopes. The results we present here benefit from the exhaustive instrumental characterization described in the first part, which relies on in-flight data.…”

First year of coordinated science observations by Mars Express and ExoMars 2016 Trace Gas Orbiter

“…Trace Gas Orbiter Temperature 5 μm [Audouard, 2014] 120-190 nm 15 µm [Grassi, 2005] 2.7~3.7µm [Vandaele, 2018, Mahieux 2012 15 µm 2.7~3.7µm Dust 2.7 μm [Vincendon, 2008] 220-290 nm * 1-1.7 μm [Mateshvili, 2007;Fedorova, 2009Fedorova, & 2014 9.3 µm 200-650 nm 2.3-4.0 μm 9.3 µm 0.7~1.7 μm, 2.3-4.0 μm Guerlet, 2019;Luginin, 2019] CO2 ice clouds 2.7μm 4.26~4.3 μm Vincendon, 2011]…”

“…3.1 μm [Madeleine, 2012;Vincendon, 2011] 300-320 nm * [Mateshvili, 2009] 12 µm [Giuranna, 2019] 300-320 nm 2.3-3.7 μm [Vandaele, 2018] 12 µm Luginin, 2019] Water vapour 2.6 μm [Melchiorri, 2006] [Encrenaz, 2006] 190-270 nm * [Cox, 2009] 4.55 ~ 5.0 µm [Billebaud, 2009] 2.3 μm [Smith, 2018;Vandaele, 2018] 2.3 µm, 4.7 µm [Smith, 2018; Methane --3.3 µm [Giuranna, 2019] 3.27 ~ 3.3 µm [Liuzzi. 2019; 3.27 ~ 3.3 µm Table 1.…”