Validation of cloud parameter retrieval methods with objective ground based measurements

To understand and model the radiative transport in a cloudy atmosphere info rmation on the cloud height and optical thickness is indispensable. Therefo re retrieval techniques for cloud parameters are developed for the AVHRR, A TSR and the future MSG. Mainly synoptic observations are used for validatio n despite their subjective nature and varying quality. To validate advanced cloud parameter retrieval methods objective physical measurements are nece ssary. At KNMI retrieval methods of cloud fraction, cloud top temperature, optical thickness and LWP from AVHRR observations are developed. Much effort is pu t in building an inf;infrastructure for validation. The retrieval methods a re validated with a two-year data set from the KNMI Cloud Detection System (CDS). Detailed analysis is performed with observations from the CLARA-camp aigns, when a number of advanced remote sensing and in-situ instruments wer e added to the CDS. The collocated lidar, radar, microwave radiometer and a ircraft measurements from the CLARA data set allow for the evaluation of th e assumptions in cloud parameter retrieval methods. Furthermore, the study presented here shows that combining measurements from lidar, radar and AVHR R provide information on cloud properties that cannot be retrieved from any of these instruments alone. (C) 1999 Elsevier Science Ltd. All rights rese rved.