Average and Peak Vegetation Growth in the United States, 1990-2005

Greenness composites have been produced for the conterminous United States every two weeks since 1989, and for Alaska, during the growing season, since 1990. The data are derived from EROS binary AVHRR time-series maximum-value NDVI (greenness) calculations, which measure vegetation cover and plant growth. Because they indicate vegetation vigor, NDVI values are commonly called greenness data. Generally, healthy vegetation is considered an indicator of favorable climatic and environmental conditions, while poor vegetation condition is indicative of droughts and diminished productivity.

Two data sets are available: average vegetation growth and peak vegetation growth. Average greenness is derived by examining all the composites for a year and calculating the arithmetic average of all the biweekly NDVI values for each pixel. These map layers are 16 images that show the average level of vegetation growth in Alaska and the conterminous United States for the years 1990 to 2005. Peak greenness is calculated by examining all of the biweekly composites for a year, pixel-by-pixel, and recording the maximum NDVI value for each pixel. Dynamic maps show monthly greenness values. The 1 km GeoTIFF maps are presently current through 2005. They are part of the USGS National Atlas.

Also see metadata for a complimentary data set, Greenness of the Conterminous United States and Alaska, registered in the ORNL Regional and Global Environmental Data (RGED) database.