<p>We will present the vertical distribution of <strong>ozone</strong> obtained from <strong>NOMAD-UVIS solar occultations</strong> and we will compare the results of three retrieval schemes.</p><p><strong>NOMAD</strong> (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 &#956;m); 2) a second infrared channel LNO (2.3-3.8 &#956;m) capable of doing nadir, as well as solar occultation and limb; and 3) an ultraviolet/visible channel <strong>UVIS</strong> (200-650 nm) that can work in the three observation modes [1,2].</p><p>The UVIS channel has a spectral resolution <1.5 nm. In the solar occultation mode it is mainly devoted to study the climatology of <strong>ozone</strong> and <strong>aerosols</strong> content [3].</p><p>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.</p><p>NOMAD-UVIS spectra are simulated using three different retrieval scheme:</p><p>1) An onion peeling approach based on [4,5] deriving slant columns at the different altitudes sounded, from which local densities are obtained;</p><p>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);</p><p>3) A direct onion peeling method deriving sequentially from top to bottom the local densities in the different layers probed.</p><p>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.</p><p><strong>References</strong></p><p>[1] Vandaele, A.C., et al., Planetary and Space Science, Vol. 119, pp. 233&#8211;249, 2015.</p><p>[2] Neefs, E., et al., Applied Optics, Vol. 54 (28), pp. 8494-8520, 2015.</p><p>[3] M.R. Patel et al., In: Appl. Opt. 56.10 (2017), pp. 2771&#8211;2782. DOI: 10.1364/AO.56.002771.</p><p>[4] Qu&#233;merais, E.,et al. J.Geophys. Res. (Planets)111, 9, 2006.</p><p>[5] Piccialli, A. et al., Planetary and Space Science, 113-114(2015) 321&#8211;335</p><p>[6] Vandaele, A.C., et al., JGR, 2008. 113 doi:10.1029/2008JE003140.</p>