Validation of POLDER/ADEOS data using a ground-based lidar network: Preliminary results for cirrus clouds

POLDER-1 on board the Japanese ADEOS platform has collected 8 months of dat a (October 1996 to June 1997). POLDER is a visible radiometer with multi-di rectional and polarization capabilities. These features allow to obtain inf ormation both on cloud thermodynamical phase and cloud altitude. The POLDER cloud algorithms are currently under validation. For cirrus clouds, a vali dation based on a comparison between cloud properties inferred from POLDER- 1 data and cloud properties retrieved from a ground-based lidar network is currently under consideration. In this paper, preliminary comparisons betwe en cloud altitude inferred from POLDER-1 and lidars are presented. These co mparisons show an underestimation of cloud altitude by POLDER-1 for optical ly thin clouds. A first theoretical analysis based on radiative transfer si mulations allows to explain the difference between POLDER and lidar altitud es. Moreover. a preliminary comparison between thermodynamical cloud phase (liquid water / ice) obtained with POLDER-1 and cloud temperature inferred from radiosoundings and cloud altitudes shows that cirrus clouds at tempera tures lower than -40 degrees C are correctly identified as ice layers by PO LDER-1 (C) 1999 Elsevier Science Ltd. All rights reserved.