Cloud cover observed simultaneously from POLDER and METEOSAT

The POLDER instrument that was aboard the Japanese ADEOS platform between A ugust 1996 and June 1997. is designed to the global observations of the pol arisation and directionality of the sun-light reflected by the Earth-atmosp here system. The cloud detection ft om POLDER takes advantage of the origin al capabilities of the instrument (spectral polarisation and directionality ). This cloud detection scheme uses 5 threshold tests based on pressure, re flectance, polarised reflectance and spectral variability. The results of t he POLDER cloud detection scheme are compared to those of the LMD dynamical clustering method applied to visible and infrared METEOSAT data and local spatial variability of these two parameters. Special focus is given to the detection capabilities of the two kind of measurements for cloud situations such as small cumulus, thin cirrus and multi-layered cloud cover. Results of this comparison would give some insight on the behaviour of the Internat ional Satellite Cloud Climatology Project (ISCCP) cloud detection scheme bu ilt mainly from visible and infrared measurements. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.