YvonneBachmannInstitute of Ecology, Evolution and Diversity, Goethe University Frankfurt, UNDESERT

YvonneBachmannassociatedParty2015-04-27NEO NASA Earth Observations, NDVI 16 day Terra MODIS, September 2000 to September 2014modis terrandviwestafricano restrictionsWestafrica-18.016.025.05.02000-09-012014-09-01YvonneBachmannInstitute of Ecology, Evolution and Diversity, Goethe University Frankfurt, UNDESERT

bachmann@bio.uni-frankfurt.de

The maps shown here, called Normalized Difference Vegetation Index (NDVI), were produced using data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra satellite. These NDVI maps are robust, empirical measures of vegetation activity at the land surface. They are designed to enhance the vegetation signal from measured spectral responses by combining two (or more) different wavebands, often in the red (0.6-0.7 mm) and near-infrared wavelengths (0.7-1.1 mm). Reflected red energy decreases with plant development due to chlorophyll absorption within actively photosynthetic leaves. Reflected near-infrared energy, on the other hand, will increase with plant development through scattering processes (reflection and transmission) in healthy, turgid leaves. Unfortunately — because the amount of red and near-infrared radiation reflected from a plant canopy and reaching a satellite sensor varies with solar irradiance, atmospheric conditions, canopy background, canopy structure, and canopy composition — one cannot use a simple measure of reflected energy to quantify plant biophysical parameters nor monitor vegetation on a global, operational basis. This problem is made more difficult due to the intricate radiant transfer processes at both the leaf level (i.e., cell constituents, leaf morphology) and canopy level (i.e., leaf elements, orientation, non-photosynthetic vegetation, and background). But Vegetation Indices circumvent these problems somewhat by combining two or more bands into an equation, such as the one for NDVI. Producing a measure of NDVI requires dividing the difference between red and near-infrared reflectance values by the sum of those same two values. The result produces a global measure of the "greenness" of vegetation across Earth's landscapes for a given composite period. These MODIS NDVI maps provide consistent, spatial and temporal comparisons of global vegetation conditions that scientists use to monitor Earth's terrestrial photosynthetic vegetation activity in support of phonologic research, change detection, and biophysical interpretations. Dark green areas show where there was a lot of green leaf growth; light greens show where there was some green leaf growth; and tan areas show little or no growth. Black means "no data."

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