GreenRevolution
Gujarat, India
SatelliteImagery
Dams
Irrigation
Desertification
Histogram of NDVI Values 1972
NDVI
Histogram of NDVI Values 1976
NDVI
Histogram of NDVI Values 1980
NDVI
The
number of pixels for each value of NDVI is plotted in the histograms above. The
red line is at 0.35, the cutoff assigned to forests using a threshold method.
The areas with NDVI values above 0.35 are shown in Figures 17-19. The
distribution is similar from year to year for most of the histogram below values
of approximately 0.2. However, the overall distribution of the data between 0.2
and 0.7 shifts slightly from year to year. One possibility is that these shifts
are caused by small errors in the process of radiometric alignment. However,
because the overall distribution of the data is not equally shifted across
vegetation abundance levels, alignment problems are less likely than the
possibility that actual changes in vegetation cover occurred.
Most importantly, the threshold method can reflect changes in the overall distribution of vegetation abundance rather than the actual changes in forest cover.