A major effort is under way, as part of the World Climate Research Program, to gather better information about clouds and their radiative effects. Since 1983 the International Satellite Cloud Climatology Project (ISCCP) has been collecting observations from surface weather stations and weather satellites to assemble two global, multiyear datasets. The dataset based on the surface weather observations describes the more traditional cloud characteristics associated with variations of weather, and it extends the back further in time. The second ISCCP dataset, made up of new satellite observations, gives the measured values of some of the key variables that determine the interaction of clouds and radiation.
Another cloud dataset is available from an earlier experimental NASA satellite (Nimbus 7); that satellite made direct measurements of radiation flux as well as of certain properties of clouds. (Radiation flux is the amount of radiation entering and leaving the top of the atmosphere per unit time.) Radiation flux measurements were then made for five more years by the Earth Radiation Budget Experiment, which gathered data from two satellites instead of only one to better fix the measured fluxes in time. Several spacecraft planned for this decade will also make measurements of radiation flux, and the World Climate Research Program has begun a coordinated effort to collect new measurements of radiation at the surface. Older data are also being examined to eliminate errors.