Vertical distributions of CO, H₂O, HDO, and temperature in the atmosphere of Mars after a year of observations with the ExoMars Trace Gas Orbiter (TGO) Atmospheric Chemistry Suite mid-infrared (ACS MIR) solar occultation spectrometer

Abstract : The ExoMars Trace Gas Orbiter (TGO) began its nominal science phase in April 2018 after arriving at the red planet in October 2016 and undergoing a lengthy aerobraking campaign. It carries a stereo camera (CaSSIS), a neutron detector (FREND), and two spectrometer suites aimed at investigating the atmosphere: the Atmospheric Chemistry Suite (ACS), and the Nadir and Occultation for Mars Discovery (NO-MAD). This presentation focuses on data analysis for the mid-infrared (MIR) channel of ACS, operating exclusively in solar occultation mode. We will describe work done to produce a Level 2B data product of calibrated transmission spectra and then show results from performing trace gas retrievals on target gas species, such as H₂O, HDO, CO, and CH₄. ACS MIR is a cross dispersion spectrometer consisting of an echelle grating with a wide blaze angle and a secondary, steerable diffraction grating (Ko-rablev et al., 2018). The secondary grating is used to separate high diffraction orders and access a spectral range of 2300-4400 cm −1. The simultaneous spectral range observed during an occultation is around 200 cm −1 wide, and the spectral resolution is around 0.04 cm −1.