In this work we present an update on the analysis described in [15,21], focused on the characterization of Martian dust microphysical properties through the investigation of the TGO/NOMAD [1] UVIS and LNO channels' combined nadir data. These observations cover ultraviolet-visible and near-infrared wavelengths respectively, an extended range that allows constraining the dust densities and sizes. Spatially and temporally coincident data are analysed through the MITRA radiative transfer (RT) tool [2,3,4,16].Being the spectral surface albedo a key element in the RT simulations, we define a method to derive it by exploiting MEx/OMEGA data. As a by-product of this analysis, we plan to obtain a global Mars surface albedo map covering visual (VIS) and near-infrared (NIR) wavelengths.Introduction Airborne dust drives the Red Planet's thermal structure and climate [6,7,8,9,10], the distribution and circulation of atmospheric gases and has a role in triggering water ice clouds formation [5,17]. These mechanisms are affected by dust composition, abundance and microphysics. The investigation of NOMAD UVIS and LNO nadir data, can provide significant information on the properties of the integrated dust column down to the surface, hence contributing in our understanding of the evolution of Mars' atmosphere.Instrument and observations Among NOMAD's three spectrometers [1], UVIS and LNO channels can observe in nadir geometry in the ultraviolet-visible (UV-VIS, 0.2 - 0.65 µm) and NIR (2.2 - 3.8 µm) ranges respectively. Therefore, if combined, they allow retrieving the dust microphysical properties in the whole atmospheric integrated column. We consider observations encompassing from the second half of Martian Year (MY) 34 to the first half of MY37, an extended interval within which dust global and seasonal trends can be analyzed.Method UVIS data are exploited down to 0.36 μm, matching the lower wavelength of the surface albedo spectra ingested in the RT model. These are obtained by processing MEx/OMEGA data with a modified version of the SAS technique [14], nominally correcting the spectral shape from the gases and aerosols contribution. We modify the method in order to determine if the observations can be considered as aerosols-free, hence avoiding biases deriving from the assumed aerosols properties in the original correction. As far as LNO is concerned, only spectral orders from 168 to 202 are adopted [15,21], since they cover a wavelength range (2.20 - 2.55 μm) that is approximately devoid of strong absorption lines, hence allowing a reliable estimation of the spectral continuum. This way, no gases correction is required in our modified SAS.The retrievals are performed through MITRA tool, deriving the temperature-pressures profiles from [11] and considering dust optical constants from [12,13]. A benchmarking with the ones recently published in [19] is also foreseen.SummaryThis study presents an update of the method described in [15,21], focused on retrieving Martian dust microphysical properties from NOMAD UVIS and LNO nadir observations. We updated the method for deriving the spectral surface albedo in order to reduce eventual biases introduced in the original correction.We plan to analyze all spatially and temporally coincident UVIS and LNO observations, in order to track the evolution of dust properties in different MYs and verify how they compare to those retrieved at high altitude with NOMAD SO channel's data [20].AcknowledgementsExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB- BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by the Spanish MICINN through its Plan Nacional and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1, ST/Y000234/1 and ST/X006549/1 and Italian Space Agency through grant 2018-2-HH.0. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the `Center of Excellence Severo Ochoa' award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This work was supported by the Belgian Fonds de la Recherche Scientifique - FNRS under grant numbers 30442502 (ET_HOME) and T.0171.16 (CRAMIC) and BELSPO BrainBe SCOOP Project. US investigators were supported by the National Aeronautics and Space Administration. 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