RETRIEVAL OF ATMOSPHERIC PROPERTIES AND SURFACE BIDIRECTIONAL REFLECTANCES OVER LAND FROM POLDER ADEOS/

Polarization and Directionality of the Earth's Reflectances (POLDER) i s a new instrument devoted to the global observation of the polarizati on and directionality of solar radiation reflected by the Earth-atmosp here system It will fly onboard the ADEOS platform in 1996. This paper outlines the improvements expected from POLDER in the description of atmospheric aerosols and water vapor over land, and of surface bidirec tional reflectances. It then gives a detailed description of the opera tional algorithms which are implemented in the ''land surface and atmo sphere over land'' processing line. This line is part of an effort ini tiated by Centre National d'Etudes Spatiales (the French Space Agency) to develop lines of products in order to facilitate the exploration o f POLDER's new capabilities by the international science community. Em phasis is given in this paper to the presentation of the principles, p hysical rationale, and elements of validation of the algorithms of thi s processing line. The main products are (1) for each orbit segment, t he amount and type of aerosols, the water vapor content, and bidirecti onal reflectances corrected for atmospheric effects, and (2) every 10 days, global maps of surface directional signatures, of hemispherical surface reflectances, and of parameters describing the statistical dis tribution of aerosol and water vapor content. These products will be m ade available to all interested investigators. The most innovative alg orithms of the processing line are (1) cloud detection, based on a ser ies of tests involving reflectance thresholds, oxygen pressure estimat es, and analysis of polarized radiance in the rainbow direction, (2) r etrieval of aerosol optical thickness and type from directional polari zed radiance measurements, and (3) retrieval of surface directional si gnature through an adjustment of a time series of directional reflecta nce measurements with a semiempirical bidirectional reflectance model.