GreenRevolution
Gujarat, India
SatelliteImagery
Dams
Irrigation
Desertification
Figure 14
Implications
of Soil & Saturation Effects in NDVI for Vegetation Change Analysis
The diagram above demonstrates the various ways that
soil and saturation problems may affect vegetation change results. The
triangular shape is representative of the scatter plot of the two methods
for detecting vegetation abundance (i.e. Figure 7). The circle represents
a single pixel changing over time. Here a pixel starts with very high percent
vegetation cover (represented by the right-most circle). If vegetation cover
decreases slightly then NDVI may not detect any change while SMA should detect
the subtle decrease. If that pixel then decreases further to an abundance that
allows for soil backgrounds to become significant, then further accuracy
problems should arise using NDVI. If the background soil of that pixel is
extremely dark then change B would be calculated as the vegetation change
according to NDVI. If that same amount of change occurred but the soil
background in that pixel was extremely bright then change A would be the
calculated vegetation change according to NDVI. However, SMA should detect the
same amount of vegetation change for that pixel regardless of the background
color (Elmore et al., 2000).