Space shuttle cloud photographs assist in correcting meteorological satellite data



The detection of clouds by satellite-borne sensors, especially those operating in the visible wavelengths, is plagued by an easily recognized but not readily eliminated problem, namely, the overestimation of cloud amount at viewing angles other than zero. An idealized cloud field is used in Figure 1 to illustrate the problem. The fraction of a fixed area which is assessed as “cloudy” increases markedly as the viewing angle £ increases, in spite of the fact that the cloud amount is uni-form. Involved is the reality that clouds have vertical as well as horizontal dimension, and at £>0, the sides as well as the tops of clouds are detected from a satellite.