Validation of the MERIS atmospheric correction over ocean using AERONET
Aznay, O.; Santer, R.; Zagolski, F. (2012). Validation of the MERIS atmospheric correction over ocean using AERONET. Adrinord/ParBleu Technologies/Université du Littoral Côte d’Opale: Lille, St Jean-sur-Richelieu and Wimereux. 1 poster pp.
Validating the atmospheric correction mainly over coastal water areas requests an ´atmospheric´ approach. Both the atmosphere and the water body present very complex and variable optical properties. By looking at water surfaces in a cloud-free scene acquired with an optical sensor such as MERIS, we observe more likely the pattern of the ocean colour rather than the spatial variability of the aerosols. Therefore, why not to use the atmospheric optical measurements rather than the marine optics?It is clear that the atmospheric correction cannot be validated only with through in-situ measurements of the aerosol optical thicknesses (AOTs). Validation of the atmospheric correction passes also by a well estimate of the atmospheric scattering components. The diffuse atmospheric transmittance can be directly provided by the sky radiance measurements. The aerosol reflectance at top of the atmosphere (TOA) can be estimated with the acquisition of the sky radiance at the same scattering angle as for the sensor/view geometry, in order to well predict the primary scattering. The introduction of the multiple scattering requires more, with the aerosol phase function (APF) and the AOT. The full protocol of the validation scheme for the atmospheric correction over ocean is described.Both in-situ measurements and MERIS level-2 data extracted from MERMAID over the AAOT site (Acqua Alta Oceanographic Tower, Venice-Italy) is employed to illustrate the methodology in a direct comparison between marine reflectances derived from the MERIS ESA Ground-Segment (MEGS) processor and extracted with an atmospheric correction based on the characterization of the inherent optical properties (IOPs) of the aerosols at the time of MERIS overpass.
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