Size distributions of clouds in real time from satellite imagery

Abstract

An instrument is proposed to gather global data on cloud size distributions. The instrument contains a broad-band visible/infrared radiometer to scan the clouds with a field of view comparable to the grid squares of circulation models, but a resolution within the field of view of approximately 100 m, adequate to resolve the fine structure of clouds. The image is digitized, discriminated to distinguish cloudy and clear pixels, and submitted to a dedicated parallel computer which calculates the size distribution of the clouds in real time. Only the size distribution is transmitted to Earth, so the data transmission rate from the satellite is low and the archival problems at the earth station are minimal. This paper examines several alternative definitions of the size distribution of clouds, and concludes that the procedure of ‘sizing by openings’ is most appropriate. It is then shown that the processing speed required by the image analyser can be achieved at realistic power levels with present day technology.