EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ozone vertical profiles from TGO/NOMAD-UVIS: an inter-comparison of three retrieval schemes

Arianna Piccialli1, Ann Carine Vandaele1, Yannick Willame1, Shohei Aoki1, Cedric Depiesse1, Loic Trompet1, Lori Neary1, Sebastien Viscardy1, Frank Daerden1, Justin Erwin1, Ian R. Thomas1, Bojan Ristic1, Jon Mason2, Manish Patel2, Alain Khayat3, Michael Wolff4, Giancarlo Bellucci5, and Jose Juan Lopez Moreno6
Arianna Piccialli et al.
  • 1Belgian Institute for Space Aeronomy (BIRA-IASB), Planetary Aeronomy, Uccle, Brussels, Belgium (
  • 2Open University, UK
  • 3NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States
  • 4Space Science Institute, Boulder, Colorado, USA
  • 5INAF, Istituto di Astrofisica e Planetologia Spaziali, Italy
  • 6IAA/CSIC, Granada, Spain

We will present the vertical distribution of ozone obtained from NOMAD-UVIS solar occultations and we will compare the results of three retrieval schemes.

NOMAD (Nadir and Occultation for MArs Discovery) is a spectrometer composed of 3 channels: 1) a solar occultation channel (SO) operating in the infrared (2.3-4.3 μm); 2) a second infrared channel LNO (2.3-3.8 μm) capable of doing nadir, as well as solar occultation and limb; and 3) an ultraviolet/visible channel UVIS (200-650 nm) that can work in the three observation modes [1,2].

The UVIS channel has a spectral resolution <1.5 nm. In the solar occultation mode it is mainly devoted to study the climatology of ozone and aerosols content [3].

Since the beginning of operations, on 21 April 2018, NOMAD UVIS acquired more than 4000 solar occultations with an almost complete coverage of the planet.

NOMAD-UVIS spectra are simulated using three different retrieval scheme:

1) An onion peeling approach based on [4,5] deriving slant columns at the different altitudes sounded, from which local densities are obtained;

2) The line-by-line radiative transfer code ASIMUT-ALVL developed at IASB-BIRA [6] using the Optimal Estimation Method to derive the local density profile in one go (on all transmittances of one occultation observation);

3) A direct onion peeling method deriving sequentially from top to bottom the local densities in the different layers probed.

We will compare results obtained from the different retrieval methods as well as their uncertainties and we will discuss the advantages and difficulties of each method.


[1] Vandaele, A.C., et al., Planetary and Space Science, Vol. 119, pp. 233–249, 2015.

[2] Neefs, E., et al., Applied Optics, Vol. 54 (28), pp. 8494-8520, 2015.

[3] M.R. Patel et al., In: Appl. Opt. 56.10 (2017), pp. 2771–2782. DOI: 10.1364/AO.56.002771.

[4] Quémerais, E.,et al. J.Geophys. Res. (Planets)111, 9, 2006.

[5] Piccialli, A. et al., Planetary and Space Science, 113-114(2015) 321–335

[6] Vandaele, A.C., et al., JGR, 2008. 113 doi:10.1029/2008JE003140.

How to cite: Piccialli, A., Vandaele, A. C., Willame, Y., Aoki, S., Depiesse, C., Trompet, L., Neary, L., Viscardy, S., Daerden, F., Erwin, J., Thomas, I. R., Ristic, B., Mason, J., Patel, M., Khayat, A., Wolff, M., Bellucci, G., and Lopez Moreno, J. J.: Ozone vertical profiles from TGO/NOMAD-UVIS: an inter-comparison of three retrieval schemes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10062,, 2021.

Corresponding presentation materials formerly uploaded have been withdrawn.