Wind Estimation from Geostationary-satellite Pictures

The motion of properly selected clouds derived from photographs taken by the geostationary Advanced Technology Satellites provides estimates of the wind a t cloud level. A large number of lowand high-cloud motions near rawin stations are compared to the balloon-derived winds to determine the levels at which these wind estimates might be used for map analyses and to assess their accuracy a t those levels. For this sample, velocities of lower clouds correspond best to winds a t 3,000 f t , while upper cloud velocities correspond best to winds at 30,000 ft . The median vector deviation of the cloud velocities from observed winds is 9 and 17 kt a t 3,000 and 30,000 f t , respectively. Direction deviations are modest; therefore, these wind estimates are ' . representative of the actual flow patterns in the lower and in the upper troposphere. Causes contributing to deviations are (1) uncertainty of cloud height, (2) nonadvective cloud motion, (3) photo-' graph-measurement errors, (4) tracking errors, and (5) unrepresentative rawinsonde observations. The principal sources of cloud-velocity deviation from observed winds are ranked in order of their significance to identify the critical areas needing improvement. It appears that cloud-height uncertainty is the most significant cause of deviations, particularly about upper cloud heights. Work aimed a t reducing this uncertainty is just beginning. To point out the unique problems involved, we discuss the technique of selecting and classifying cloud targets. The procedure is a subjective skill dependent upon the analyst's meteorological judgment. Despite the problems-many as yet unsolved-the single earth-synchronous satellite, with its immense areal coverage and high frequency of coverage, provides an important new source of data from remote regions.