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Measuring Raindrops By Satellite

Satellites are useful for monitoring weather patterns, even down to the size of raindrops. While doing his PhD in Auckland University's Physics Department, Don Grainger used satellite data from the NZ Meteorological Service to determine cloud droplet size.

The resolution of the satellite is normally 1.1 kilometres, but changes in droplet size of as little as two microns could be detected from changes in the way the clouds reflected sunlight. Satellite observation of clouds moving over the Tararuas showed a steady increase in cloud droplet size on the windward side of the mountains and a decrease on the leeward size.

Grainger says that this research has useful applications for global warming studies. A rise in pollution increases the number of particles on which water vapour condenses and reduces the average size of droplets. The ability to remotely measure cloud droplet size will take some of the guesswork out of radiation budget studies, Grainger says.