INHERENT OPTICAL PROPERTIES OF THE AEROSOLS FOR OLCI/SENTINEL-3: FROM MICRO-PHYSICAL PROPERTIES TO OPTICAL PROPERTIES USING AERONET

摘要

A well-knowledge of the aerosol optical propertiesrn(AOPs) is a strong requirement for achieving thernatmospheric correction over ocean. Since several decades,rnthese AOPs were computed with standard aerosolrnmodels (SAMs) characterized by their micro-physicalrnproperties. From the characteristics of microphysicsrncan be derived the inherent optical properties (IOPs).rnThese SAMs were still used in the generation of thernMERIS (Medium Resolution Imaging Spectrometer)rnauxiliary data files (ADFs) to feed the atmosphericrncorrection algorithm. This approach has been recentlyrnrevisited by using models derived from the analysis ofrnthe AERONET (Aerosol Robotic NETwork) measurementsrn[1]. Alternatively, IOPs of these aerosols couldrnbe directly extracted from these AOPs [2].rnThese two approaches have been compared by startingrnto build a database with aerosol IOPs over fourrnAERONET stations in the Northern Sea plus one at thernAcqua Alta Oceanographic Tower (AAOT, Venice -rnItaly). Several thousands of data sequences withrnaerosol IOPs were processed with filtering techniquesrnand statistical methods to produce 16 classes ofrnaerosols. An analysis of the dispersion of the IOPs inrneach class has been conducted first, to translate thisrndispersion into an error on the aerosol model extractedrnin the near-infrared (NIR) domain from space. Second,rnwe have evaluated how well the aerosol reflectance canrnbe predicted in the visible (VIS) region in the frame ofrnthe ocean colour observation. The first objectivernconsisted in a direct comparison between the twornapproaches to derive the IOPs of the aerosols fromrnAERONET.rnMoreover, the need to account for a seasonal andrnregional variability of the aerosol models has been alsornanalyzed, as well the potential that could offer a biangularrnviewing geometry (such as with AATSR,rnAdvanced Along-Track Scanning Radiometer) in arnfiner identification of the aerosol IOPs. The possiblernconsequence of the OLCI/S3 (Ocean & Land ColourrnInstrument onboard Sentinel-3) tilt on the characterizationrnof the aerosols is finally discussed.