EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-5508 Assessing VIIRS aerosol data assimilation as a MODIS successor in the NASA GEOS system Buchard Virginie 1 2 Castellanos Patricia https://orcid.org/0009-0005-5959-5808 2 da Silva Arlindo M. 2 3 4 Govindaraju Ravi 5 2 Thompson Matthew A. https://orcid.org/0000-0001-6222-6863 5 2 Levy Rob https://orcid.org/0000-0002-8933-5303 6 Lee Jaehwa 6 7 Kim Vincent https://orcid.org/0000-0002-0445-4806 8 9 Gupta Pawan https://orcid.org/0000-0002-0979-472X 10 Goddard Earth Sciences Technology and Research II (GESTAR II), University of Maryland Baltimore County, Baltimore, Maryland, USA Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Center for Research on Sustainable Forests, University of Maine, Orono, Maine, USA Asticou Earth Systems LLC, Bar Harbor, Maine, USA Science Systems and Applications, Inc., Lanham, Maryland, USA Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA Entarian, Greenbelt, Maryland, USA NOAA Weather Prediction Center - Extended Prediction Division, College Park, MD, USA Biospheric Science Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 29 09 2026 2026 1 40 Copyright: © 2026 Virginie Buchard et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5508/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5508/egusphere-2026-5508.pdf

Aerosol data assimilation is critical for global Earth system modelling, improving aerosol optical depth (AOD) representation for weather and atmospheric composition forecasts and reanalyses. MODIS sensors on Terra and Aqua were the primary observation source for operational aerosol assimilation within the NASA Goddard Earth Observing System (GEOS). As MODIS nears decommission, VIIRS aboard NOAA satellites represent its successor. This transition trades the MODIS morning satellite for VIIRS&rsquo;s increased data volume, gapless equatorial coverage, and finer spatial resolution. This study assesses the assimilation of VIIRS NOAA-20 AOD within GEOS.</p> <p>To ensure observing platform consistency, GEOS uses a Neural Network Retrieval (NNR) algorithm translating radiances into AERONET-calibrated AOD, homogenizing aerosol observations before assimilation. Two experiments (March 2019&ndash;February 2020) compared a control assimilating NNR MODIS Terra/Aqua against a test assimilating NNR VIIRS NOAA-20.</p> <p>Validation against AERONET and Maritime Aerosol Network observations shows that, despite lacking a morning satellite, VIIRS alone performs competitively with combined MODIS, with comparable correlations and error metrics. Relative performance varies by aerosol regime. In dust-dominated environments, VIIRS frequently yields better agreement with AERONET due to finer resolution and greater data volume. During biomass burning, MODIS shows a slight advantage from stronger diurnal constraints on rapidly varying smoke plumes. Both experiments underestimate peak AOD during wildfires (stemming from the &sim;<span>50 km grid artificially diluting concentrated smoke) and in African mixed-aerosol highlands (driven by topographic smoothing). Overall, VIIRS observational density compensates for reduced temporal sampling, supporting a reliable transition for GEOS aerosol forecasting and reanalyses.</span>

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