The animation will play through once automatically. To replay, click the play button. To step through frames individually, use the left and right arrows on the bottom right corner of the animation box or the left and right arrows on the keyboard. Background: To measure and map the density of green vegetation across the Earth’s landscapes, scientists use satellite sensors that observe the distinct wavelengths of visible and near-infrared sunlight that is absorbed and reflected by the plants. Calculating the ratio of the visible and near-infrared light reflected back up to the sensor yields a number from minus one (-1) to plus one (+1). The result of this calculation is called the Normalized Difference Vegetation Index, or NDVI. An NDVI value of zero means no green vegetation and close to +1 (0.8 - 0.9) indicates the highest possible density of green leaves. Scientists now have a modified green vegetation data set called FASIR NDVI. In short, FASIR NDVI is a highly corrected global data set composited into one-month time periods. Scientists removed a variety of erroneous artifacts from the data, ranging from sensor degradation, to volcanic aerosol effects, cloud contamination, short-term atmospheric effects (e.g., water vapor and aerosol effects), sun angle variations, and missing data. These data were collected from January 1982 through December 1990 by the Advanced Very High Resolution Radiometer (AVHRR) flying aboard NOAA-7, NOAA-9, and NOAA-11 satellites. (“FASIR” stands for Fourier-Adjusted, Solar-zenith-angle corrected, Interpolated, Reconstructed data.) By precisely measuring the radiant energy emitted from Earth’s surface, satellites can determine temperature at the surface-atmosphere boundary. Surface temperature influences the rate at which water evaporates, as well as wind and precipitation patterns and the formation of clouds. (Data from TIROS Operational Vertical Sounder [TOVS]) Questions: Discuss some of the patterns you see in the animation. In general, why does higher surface temperature contribute to an increase in the amount of vegetation productivity? Carefully observe the changes in temperature and in vegetation from March 87 to July 87 at high northern latitudes. Does green vegetation increase at the same time surface temperature increases? Or, is there a lag between the two? Why does higher surface temperature have no effect on vegetation in some of the regions? Links: Changing Global Land Surface (http://Earthobservatory.nasa.gov/Library/LandSurface/)   Measuring Vegetation (http://Earthobservatory.nasa.gov/Library/MeasuringVegetation/)   From the Dust Bowl to the Sahel (http://Earthobservatory.nasa.gov/Study/DustBowl/)   Growing Data (http://Earthobservatory.nasa.gov/Study/GrowingData/)   Should We Talk about the Weather? Improving Global Forecasts with BOREAS Research (http://earthobservatory.nasa.gov/Study/BOREASAlbedo/)   Mission: Biomes (http://earthobservatory.nasa.gov/Laboratory/Biome/)   next activity (#9): Comparing outgoing heat radiation to cloud fraction during the period of February 1988 to February 1990 previous activity (#7): Comparing cloud fraction to reflected shortwave radiation from November 1984 to February 1990

	Subscribe to the Earth Observatory About the Earth Observatory Contact Us Privacy Policy and Important Notices Responsible NASA Official: Lorraine A. Remer Webmaster: Goran Halusa We're a part of the Science Mission Directorate