Specification of current and future cloud amounts and ceilings from satellite data /

Objective methods and their accuracies for deriving current and six-hour forecasts of cloud amount and ceiling from satellite data are presented. Data from the visible and IR window bands were tested to develop relationships. The IR data did not significantly improve the results. The visible data were carefully calibrated, navigated, and normalized for solar elevation and bidirectional reflectance. Cloud motions were also used for the six-hour forecasts. The data were reduced to values of average brightness and its standard deviation over 1/2 deg by 1/2 deg areas before analysis. RMSE of current cloud amounts (on a scale of 0 to 1) are about 0.25 and for six hours later about 0.35. The occurrence of a ceiling/no ceiling was specified correctly 80% and 70% of the time at zero and six hours, respectively. Various methods are shown for minimization of ceiling errors over different height ranges. In general, RMSE of specified and forecast ceilings range from 4000 to 6000 ft at low levels to 9000 to 10,000 ft at mid and high levels. (Author)."Meteorology Laboratory Project 6698.""ADA021895 (from http://www.dtic.mil).""9 December 1975."Includes bibliographical references (pages 25-26).Objective methods and their accuracies for deriving current and six-hour forecasts of cloud amount and ceiling from satellite data are presented. Data from the visible and IR window bands were tested to develop relationships. The IR data did not significantly improve the results. The visible data were carefully calibrated, navigated, and normalized for solar elevation and bidirectional reflectance. Cloud motions were also used for the six-hour forecasts. The data were reduced to values of average brightness and its standard deviation over 1/2 deg by 1/2 deg areas before analysis. RMSE of current cloud amounts (on a scale of 0 to 1) are about 0.25 and for six hours later about 0.35. The occurrence of a ceiling/no ceiling was specified correctly 80% and 70% of the time at zero and six hours, respectively. Various methods are shown for minimization of ceiling errors over different height ranges. In general, RMSE of specified and forecast ceilings range from 4000 to 6000 ft at low levels to 9000 to 10,000 ft at mid and high levels. (Author).Mode of access: Internet