This is the story -“Satellite captures Earth’s greenery-carried by Science Daily,Web edition: June 21, 2013.
Authored by Cristy Gelling,it says that orbiting camera detects reflected light to determine extent of vegetation.
“A new instrument onboard the NASA–NOAA Suomi satellite has been capturing exquisitely detailed views of seasonal and environmental shifts in plant cover. Light sensors on the satellite identify vegetation by detecting differences in reflected amounts of visible light, which plants absorb for photosynthesis, and near-infrared light, which plants don’t absorb. Subtle changes in greenness can give advance warning of drought or fire conditions. Meteorologists can also use data on vegetation dynamics to improve weather prediction’,said the story.