NDVI is a commonly used vegetative index in remote sensing analysis to distinguish the vegetation from non-vegetation features recorded in satellite images.
NDVI or Normalized Differentiate Vegetation Index is a vegetative index derived from satellite image by the ratio formula of Near Infra Red (NIR) band and Red (R) band. It is the most common vegetation indices used in remote sensing technology to analyze the plant greenness.
NDVI = NIR – R
NIR + R
*NIR = Near Infra Red Band Wavelength
R = Red Band Wavelength
It’s an index which differentiates between the vegetative portion recorded by the satellite image with other observed objects including water bodies, buildings, bare lands and others. The differentiation is assessed by the given value derived from the formula which stands between -1 to 1. Value which is positive (relatively between 0.2 and 0.9) is considered as green vegetation while the value below of the range usually represents other non-vegetative object. The closer a value to 1 indicates the healthiness of the vegetation.
Green vegetation absorbs incoming radiation at visible light but reflects some of the green wavelength and also all the near infra-red wavelength. This is why the vegetation looks green to our eyes just like we see the ocean blue because it reflects most of the blue wavelength of the visible light. Although vegetation NIR wavelength reflects more, doesn’t mean we can see a plant or tree in infrared wavelength color because human eyes can only see the visible portion of light which is between the wavelengths of 390 and 750nm. However, human eye can distinguish up to 1 million color surfaces (1).
|Vegetation spectral curve|
Remote sensing application
Because of its practicality and relevance, NDVI is used and accepted worldwide as a vegetation index in forestry study and management to analyze the plant characteristics from satellite image via remote sensing technology. Some of its uses include assessing and monitoring of vegetation dynamics or plant phonological changes over time, biomass production, grazing impacts or attributes related to grazing management, changes in rangeland condition, carbon sequestration or CO2 flux, soil moisture and vegetation or land cover classification (2).
Monitoring regional and global NDVI
It is in great interest and importance to monitor the vegetation as they are the primary source of our O2. At global level, NASA played a part with its Earth Observatory program by providing global maps for general view of what’s happening on our planet which include the vegetation (3). However, a monitoring at regional scale is also vital as to provide more accurate information of one area on the healthiness of the vegetation.
Global NDVI map as of September 2010 (Source: NASA Earth Observatory (NEO))