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Spring Vegetation in North America
This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science.
Vegetation indices are important tools in the monitoring,
mapping, and resource management of the Earth's terrestrial vegetation.
They are radiometric measures of the amount, structure, and condition of
vegetation which serve as useful indicators of seasonal and inter-annual
variations in vegetation. 16 days of Moderate Resolution Imaging Spectroradiometer
(MODIS) images from the period from March 5 through March 20, 2000,
were atmospherically corrected and then composited. The resulting
composited reflectances in the first 4 bands of MODIS (blue, green, red,
and near infrared) were then used as input into the computation of the NDVI and EVI.
The MODIS sensor offers many improvements for vegetation index products,
including improved sensitivity to chlorophyll and less contamination by
atmospheric water vapor through narrower bandwidths in the red and near infrared,
respectively. In addition, the finer pixel size (250 meter red and near
infrared bands) provides improved vegetation index monitoring and change
detction capability. The MODIS vegetation index products are produced at
spatial resolutions of 250m, 500m, 1km and 0.25 degrees, and at temporal intervals
of 16 days and 1 month. They include two
vegetation index formulations, the normalized difference vegetation index, NDVI, which
will serve as a 'continuity' index to extend the Advanced Very High Resolutiuon Radiometer
NDVI data record. An improved, or enhanced vegetation index (EVI) is also produced with the
goal of providing complementary information on the spatial and
temporal variations of vegetation, while minimizing much of the contamination problems
present in the NDVI, such as those associated with canopy background and
residual aerosol influences. Whereas the NDVI is chlorophyll
sensitive and responds mostly to red band variations, the EVI is more NIR
sensitive and responsive to canopy structural variations, including leaf area index,
canopy type, and canopy architecture.
To view vegetation data over time, go to
Vegetation in Data & Images.
Images and text courtesy the Department of Soil, Water, and Environmental Sciences at the University of Arizona