Animation of North America's NDVI over the course of a year
| The above animation shows the level of "greenness" across North America for the period beginning February 1995 and ending January 1996. This "greenness" index (called the Normalized Difference Vegetation Index, or NDVI) is a measure of how green a surface appears from above. The "greenness" of a certain part of the Earth is directly related to how much vegetation exists there at a certain time. Sensors on satellites in orbit above our planet record certain levels of light (in this case, infrared and red light) that bounce off the surface, and send that data down to receiving stations on Earth. Scientists are then able to make large-area maps of vegetative vigor from this data. This movie shows how the vegetation changes throughout North America over the course of a year. Notice how much greener the continent is during the summer (June, July and August) than it is during the winter. |
Credit: Dylan Prentiss, Department of Geography, UCSB
For more info: http://www.geog.ucsb.edu/~dylan/mtpe/biosphere/topics/veg/ndvi.html