First results of the POLDER "Earth Radiation Budget and Clouds" operational algorithm

The POLDER instrument is devoted to global observations of the solar radiat ion reflected by the earth-atmosphere system. Algorithms of the "Earth Radi ation Budget and Clouds" processing line implemented at the French Space Ce nter are applied to ADEOS-POLDER data. First results on derived cloud prope rties are presented from POLDER level 2 data of 10 November 1996 and level 3 products of June 1997. A good correlation is observed between the POLDER cloud detection algorithm and the Dynamical Clustering Method applied to METEOSAT data. The multidir ectional capability of POLDER appears useful to check schemes of cloud opti cal thickness retrieval. As expected, a water droplet model is suitable for liquid water clouds and inadequate for ice clouds. That indirectly validat es our algorithm of cloud phase recognition. An apparent pressure is derive d from O-2-absorption measurements and a Rayleigh cloud pressure from polar ization observations. For overcast conditions, the apparent pressure is lar ger (by more than 100 hPa) than the Rayleigh pressure chiefly due to the ph oton penetration effect. For partly cloudy conditions, it can be larger or weaker depending on the surface reflectivity. Preliminary comparisons between POLDER and ISCCP monthly mean products outl ine some differences resulting in part from the original characteristics of POLDER.