Vegetation Indices Maps

Vegetation indices maps are useful indicators of vegetation cover and can help in distinguishing various land cover classes. We used the Normalized Difference Vegetation Index (referred to as NDVI from here on) to document and evaluate the changes in the vegetation cover in our study region and also as a means of identifying useful land cover classes for this study. The spectral bands used for this purpose were the red and near infrared bands as active terrestrial vegetation strongly absorbs red light and strongly reflects near infra-red energy. The NDVI maps were created using the following formula (Tucker 1979):

NDVI = (Near Infrared Band – Red Band) / (Near Infrared Band + Red Band)                        (3)

where for all the datasets,

NIR band = Band 40 reflectance file

Red band = Band 30 reflectance file

The NDVI generated maps shown in figure 3 below were successful in identifying at least five different land use and land cover features of the study region. These included water bodies (NDVI values -0.4 to -0.1), rocky regions, cliff faces and shadows (NDVI values -0.1 to 0), areas of no vegetation- mostly bare soil (0 to 0.2), light to moderate vegetation (NDVI values 0.2 to 0.5), and dense vegetation (NDVI values 0.5 to 0.8). 

Figure 3. NDVI maps of the study region from 1991, 2000, 2009, 2010, and 2011 that highlight the extent of and changes in the vegetation and other land use and land cover features over both decadal and yearly time scales. The NDVI values range from -0.27 to 0.77. The negative values (in blue) represent water bodies whereas the positive values (in green) represent areas with vegetation with higher values (in dark green) representing dense forest cover and those in light green representing light to moderate vegetation cover. Values close to 0 and slightly negative (in yellow and brown) show land not covered by vegetation and includes bare soil (yellow) and rocky areas, cliff faces and their shadows (dark brown).