Removal of straylight from ExoMars NOMAD-UVIS observations

Mason, Jonathon; Patel, Manish; Leese, Mark; Hathi, Brijen; Willame, Yannick; Thomas, Ian R.; Wolff, Michael J.; Depiesse, Cédric; Holmes, James; Sellers, Graham; Marriner, Charlotte; Ristic, Bojan; Daerden, Frank; Lopez-Moreno, Jose Juan; Bellucci, Giancarlo and Vandaele, Ann Carine (2022). Removal of straylight from ExoMars NOMAD-UVIS observations. Planetary and Space Science, 218, article no. 105432.

DOI: https://doi.org/10.1016/j.pss.2022.105432

Abstract

We present an in-flight straylight removal method for the Ultraviolet and Visible Spectrometer (UVIS) channel of the Nadir and Occultation for Mars Discovery (NOMAD) instrument aboard the ExoMars Trace Gas Orbiter (TGO). The presence of a ‘red-leak’ straylight signal in the UVIS instrument was discovered post-launch in ground calibration measurements of spectral lamps; UVIS observations of lamps with negligible UV light emission (RS12) showed a significant signal at UV wavelengths. Subsequent analyses of nadir observations of the martian atmosphere revealed that at UV wavelengths the red-leak straylight was in excess of 300% of the true UV signal, jeopardising the primary science observations of the instrument (retrievals of atmospheric ozone). By modifying the UVIS readout method to obtain a region of interest around the illuminated region on the Charge-Coupled Device (CCD) detector, instead of a binned one-dimensional spectrum, and utilising straylight profiles derived from measurements of the RS12 calibration lamp we show that the majority of the straylight at UV wavelengths can be successfully removed for the nadir channel in a self-consistent manner. The corrected UVIS radiances are compared to coincident Mars Color Imager (MARCI) instrument observations with residuals between the two instruments generally remaining within 15%.

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• Item ORO ID
• 82212
• Item Type
• Journal Item
• ISSN
• 0032-0633
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Not Set	ST/V002295/1	UKSA
  Not Set	ST/V005332/1	UKSA
  Surface/atmosphere interactions from above and below.	ST/S00145X/1	UKSA UK Space Agency
  ExoMars TGO: CaSSIS operations	ST/R003025/1	UKSA UK Space Agency
  Not Set	Not Set	Belgian Science Policy Office (BELSPO)
  Not Set	PEA 4000103401	ESA Prodex Office
  Not Set	PEA 4000121493	ESA Prodex Office
  Not Set	PGC2018-101836-B-I00	Spanish Ministry of Science and Innovation (MCIU
  MINECO/FEDER	ESP2017-87143-R	Not Set
  Not Set	2018-2-HH.0	Italian Space Agency
  ET_HOME	30442502	Belgian Fonds de la Recherche Scientifique
  Center of Excellence Severo Ochoa	SEV-2017-0709	State Agency for Research of the Spanish MCIU
  Not Set	Not Set	National Aeronautics and Space Administration

• Keywords
• Straylight removal; Ultraviolet–visible spectroscopy
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Copyright Holders
• © 2022 The Authors
• Depositing User
• ORO Import