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.