To determine the density of green on a patch of land, researchers must observe the wavelengths of visible and near-infrared sunlight reflected by the plants. The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 um - 0.7 um). Vegetation strongly reflects near-infrared light (from 0.7 -1.0 um). The more healthy leaves a plant has, the more the the visible light will be absorbed and the near-infrared will be reflected. In this animation, dark green indicates dense, healthy vegetation, whereas beige areas represent bare soil. Snow from the MODIS instruments is overlaid on top.
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 126.96.36.199.0