Aerosol remote sensing over land: A comparison of satellite retrievals using different algorithms and instruments

An inter-comparison study of the aerosol optical thickness (AOT) at 0.55 μm retrieved using different satellite instruments and algorithms based on the analysis of backscattered solar light is presented for a single scene over central Europe on October 13th, 2005. For the first time comparisons have been performed for as many as six instruments on multiple satellite platforms. Ten different algorithms are briefly discussed and inter-compared. It was found that on the scale of a single pixel there can be large differences in AOT retrieved over land using different retrieval techniques and instruments. However, these differences are not as pronounced for the average AOT over land. For instance, the average AOT at 0.55 μm for the area 7–12E, 49–53N was equal to 0.14 for MISR, NASA MODIS and POLDER algorithms. It is smaller by 0.01 for the ESA MERIS aerosol product and larger by 0.04 for the MERIS BAER algorithm. AOT as derived using AATSR gives on average larger values as compared to all other instruments, while SCIAMACHY retrievals underestimate the aerosol loading. These discrepancies are explained by uncertainties Abbreviations: AATSR, Advanced Along Track Scanning Radiometer; AERONET, AErosol Robotic NETwork; AFVI, Aerosol Free Vegetation Index; AOT, Aerosol Optical Thickness; BAER, Bremen AErosol Retrieval; CNES, French Space Agency; CNR, Italian National Research Council; ECMWF, European Center for Medium range Weather Forecasting; ENVISAT, ENVIronmental SATellite of the European Space Agency; ESA, European Space Agency; IPCC, Intergovernmental Panel on Climate Change; ISAC, Institute of Atmospheric Sciences and Climate; JPL, Jet Propulsion Laboratory; MERIS, MEdium Resolution Imaging Spectrometer; MISR, Multi-angle Imaging SpectroRadiometer; MODIS, MODerate resolution Imaging Spectroradiometer; NASA, NAtional Space Administration; PARASOL, Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar; POLDER, POLarization and Directionality of the Earth's Reflectances; SCIAMACHY, SCanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY; TOA, Top of Atmosphere. ⁎ Corresponding author. E-mail address: [email protected] (A.A. Kokhanovsky). 0169-8095/$ see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2007.02.008 373 A.A. Kokhanovsky et al. / Atmospheric Research 85 (2007) 372–394 in a priori assumptions used in the different algorithms and differences in the sensor characteristics. Validation against AERONET shows that MERIS provides the most accurate AOT retrievals for this scene. © 2007 Elsevier B.V. All rights reserved.