Satellite data can gauge the health of plants, which is a good indicator of drought. The Normalized Difference Vegetation Index (NDVI) measures how dense and green plant leaves are. NDVI images are useful as a measure of drought when compared to 'normal' plant health. Scientists calculate average NDVI values for an area to find out what is normal at a particular time of year. This animation uses satellite imagery to show changes in vegetation between 1999 and 2003. In 2002, drought had settled across the Midwest. Large dark brown sections of eastern Colorado show where vegetation was less lush and healthy than normal. This version of the visualization is a wide view showing the western United States. The data were measured by the vegetation instrument on Europe's SPOT-4 satellite, and were provided by DigitalGlobe/SPOT under agreement with the U.S. Department of Agriculture Foreign Agricultural Service (USDA/FAS).
This animation shows NDVI over the western US in ten-day intervals from 1999-06-10 through 2003-09-30. The area shown extends from California to Colorado, and from Canada to Mexico. The horizontal scale is 0.0735 degrees-pixel in the E-W direction and 0.0450 degrees-pixel N-S.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 22.214.171.124.0