ON THE SAMPLING OF AIRBORNE MEASUREMENTS OF RADIATIVE PROPERTIES OF CLOUD FIELDS - RESULTS FROM INTERNATIONAL CIRRUS EXPERIMENT (ICE), 1987

During the first pilot phase of the International Cirrus Experiment (I CE) in September/October 1987 radiation measurements were carried out above and below broken cloud fields over the German Right. Analyses of the measurements of 25.9.1987 (broken cumulus cloud held) showed an u nexpected high ''absorption'' of solar radiation but not those of 28.9 .1987 (stratocumulus/stratus cloud field). This might be explained by a partial negligence of cloud side factor under the viewing geometry o f the pyranometer and other reasons. The light guide effect (''leakage '') within holes can account for the depletion of cloud reflectance an d the enhancement of cloud transmittance at large cloud cover, as obse rved during the measurements on 28.9.1987. The fluctuation of the irra diances, which can be characterized by the intermittency parameter, ha s been related to the corresponding cloud cover by a regression equati on. On the condition of similarity, this scaling parameter derived fro m sample measurements could be extrapolated to that of the whole cloud field. Thus, the estimation of the irradiance spectrum for the whole cloud field may be possible, from samples taken with aircraft and imag ing data.