Vegetation Indices Maps

Vegetation indices maps are useful indicators of vegetation cover and can help in distinguishing various land cover classes. We use 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 as a means of identifying useful land cover classes for this study. The spectral bands used for this purpose are the red and near infrared bands as active terrestrial vegetation strongly absorbs red light and strongly reflects near infra-red energy. Mathematical combinations of these bands are used for the computation of different vegetation indices.

The NDVI maps were created using the following formula (Tucker, 1979):

NDVI = (Near Infrared Band – Red Band) / (Near Infrared Band + Red Band)            (1)

where for the datasets from the year 2000,

NIR band = Band 40 reflectance file

Red band = Band 30 reflectance file

and for the datasets from the year 2014,

NIR band = Band 50 reflectance file

Red band = Band 40 reflectance file

The NDVI generated maps range between -1 (no vegetation) to + 1 (maximum vegetation). Typically clouds, water and snow have negative NDVI since they are more reflective in visible (red) than near IR wavelengths. Soil and rock have a broadly similar reflectance (NDVI around 0) and active vegetation has a positive NDVI, typically between about 0.1 and 0.6.

NDVI map of the Indian Sundarbans from the year 2000. The NDVI values range from -0.09 to 0.52. The negative values (in blue) represent areas of no vegetation, in this case water mainly whereas the positive values (in green) represent areas with vegetation. Values shown in brown represent suspended sediments

NDVI map of the Indian Sundarbans from the year 2014. The NDVI values range from -0.09 to 0.52.

NDVI map of the Bangladesh Sundarbans from the year 2000. The NDVI values range from scale bar ranges from -0.14 to 0.36. The negative values (in blue) represent areas of no vegetation, in this case water mainly whereas the positive values (in green) represent areas with vegetation. Values in brown color represent suspended sediments. 

NDVI map of the Bangladesh Sundarbans from the year 2014. The NDVI values range from scale bar ranges from -0.14 to 0.36.