Pixel‐scale composite top‐of‐the‐atmosphere clear‐sky reflectances for Meteosat‐7 visible data

A new method to estimate composite top of the atmosphere (TOA) visible clear‐sky reflectances for wide narrow band geostationary satellites such as the Meteosat constellation is presented. This method relies on some a priori knowledge of angular variations of TOA broadband reflectances associated with clear‐sky conditions above mean surface types through the use of the clear‐sky Cloud and the Earth's Radiant Energy System (CERES) shortwave broadband angular dependency models (ADMs). Each pixel (or Earth location) viewed from such geostationary imager at a given daytime is associated with a reflectance time series made up of its chronological daily measurements. This time series can be seen as a clear‐sky visible narrow band reflectance curve of the associated pixel surface plus an additive random noise modeling cloudy conditions above it. On the basis of this assumption, TOA clear‐sky broadband reflectances extracted from the CERES ADMs are used to compute curve‐driven fifth percentiles on these time series in order to estimate the TOA clear‐sky visible narrow band reflectance curves for all pixels, while the percentile approach exhibits only a reduced sensitivity to cloud shadows. Benefits of our method are discussed with respect to its application to 7 months of Meteosat‐7 daytime visible narrow band measurements. Finally, the performance of our algorithm is assessed through comparisons with its predicted and associated International Cloud Climatology Project DX clear‐sky values with respect to a visually generated clear‐sky pixels database.