The map layers representing Normalized-Difference Vegetation Index
(NDVI) monthly maxima for 1993 have been acquired
from USGS (Jones 1996). NDVI is the difference of near-infrared
(AVHRR Channel 2) and visible (AVHRR Channel 1) reflectance values
divided by total reflectance as follows:
NDVI values may range from -1.0 to 1.0, where negative values
generally represent clouds, snow, water, and
other non-vegetated surfaces while positive values represent vegetated
surfaces. In order to scale the computed NDVI results to byte data range the
NDVI datarange of -1.0 to 1.0 is scaled to the range of 0 to 200, where computed
-1.0 equals 0, computed 0 equals 100, and computed 1.0 equals 200. As a result,
NDVI values of less than 100 now represent clouds, snow, water, and other
non-vegetative surfaces and values greater than 100 represent vegetative
surfaces (Kidwell 1986). In our maps the minimum value was 71 and the maximum
was 173. To use the maximum number of colors in our maps we took only this
interval.
Click on the month to see individual maps
Click here to see the movie for NDVI change.
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