Abstract:
The International Satellite Cloud Climatology Project (ISCCP), the
first project of the World Climate Research Program (WCRP), was
established in 1982 (WMO-35 1982, Schiffer and Rossow 1983):
- To produce a global, reduced resolution, calibrated and normalized
radiance data set containing basic information on the properties of the
atmosphere from which cloud
... parameters can be derived.
- To stimulate and coordinate basic research on techniques for inferring
the physical properties of clouds from the condensed radiance data set
and to apply the resulting algorithms to derive and validate a global
cloud climatology for improving the parameterization of clouds in
climate models.
- To promote research using ISCCP data that contributes to improved
understanding of the Earth's radiation budget and hydrological
cycle.
Since 1983 an international group of institutions has collected and
analyzed satellite radiance measurements from up to five geostationary
and two polar orbiting satellites to infer the global distribution of
cloud properties and their diurnal, seasonal and interannual
variations. The primary focus of the first phase of the project
(1983-1995) was the elucidation of the role of clouds in the radiation
budget (top of the atmosphere and surface). In the second phase of
the project (1995 onwards) the analysis also concerns improving
understanding of clouds in the global hydrological cycle.
The ISCCP analysis combines satellite-measured radiances (Stage B3
data, Schiffer and Rossow 1985), Rossow et al. 1987) with the TOVS
atmospheric temperature-humidity and ice/snow correlative data sets to
obtain information about clouds and the surface. The analysis method
first determines the presence of absence of clouds in each individual
image pixel and retrieves the radiometric properties of the cloud for
each cloudy pixel and of the surface for each clear pixel. The pixel
analysis is performed separately for each satellite radiance data set
and the results reported in the Stage DX data product, which has a
nominal resolution of 30 km and 3 hours. The Stage D1 product is
produced by summarizing the pixel-level results every 3 hours on an
equal-area map with 280 km resolution and merging the results from
separate satellites with the atmospheric and ice/snow data sets to
produce global coverage at each time. The Stage D2 data product is
produced by averaging the Stage D1 data over each month, first at each
of the eight three hour time intervals and then over all time
intervals. 
