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An important source of uncertainty in radiative forcing of climate models is their treatment of tropospheric aerosols. Satellite radiometry offers the only means of providing aerosol characterization on a global scale. POLDER (POLarization and Directionality of the Earth's Reflectances) instrument was launched in August 1996 on the ADEOS platform. Aerosol products are derived from combination of multiangular, multispectral and polarized observations in visible and near infrared bands. Validation effort has been planned to test POLDER aerosol products by comparison to independant measurements. The validation is achieved using ground based sunphotometers from a worldwide station network and by performing or participating to specific campaign such as ACE-2 (Aerosol Characterization Experiment) for marine and desert dust aerosol, AMT-4 (Atlantic Meridian Transect) with a ship crossing from Falklands to England (marine aerosol) and to continental campaigns in France (urban and continental aerosol). In the paper, two aspects of the validation will be presented. The first point concerns the analysis of data acquired during the specific campaigns. In that case, sunphotometer and polarimeter measurements will be qualitatively analysed but also used into comparison with POWER model database. In a second step, we shall report systematic studies of the worldwide sunphotometer network measurements (statistic on aerosol loading, Angstrom coefficient related to particle size). First results of these statisical studies will be presented and will be taken into account in the aerosols model database used into the POLDER aerosol algorithm. Keywords: POLDER, aerosols, polarization, validation.
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