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6- monthly NDVI average for Australia, 1 Dec 2012 to 31 May 2013 [1]. A vegetation index (VI) is a spectral imaging transformation of two or more image bands designed to enhance the contribution of vegetation properties and allow reliable spatial and temporal inter-comparisons of terrestrial photosynthetic activity and canopy structural variations.
Modifiable areal unit problem (MAUP): NDVI is ubiquitous as an index of vegetation. Since mapping and monitoring of vegetation takes place via ‘big data’ image processing systems. These systems may use pixel- or object-based algorithms to assess vegetation health, evapotranspiration, and other ecosystem functions. When a category of ...
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Together the instruments image the entire Earth every 1 to 2 days. They are designed to provide measurements in large-scale global dynamics including changes in Earth's cloud cover , radiation budget and processes occurring in the oceans, on land, and in the lower atmosphere .
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2011 Enhanced vegetation index based on MODIS Terra data. The enhanced vegetation index (EVI) is an 'optimized' vegetation index designed to enhance the vegetation signal with improved sensitivity in high biomass regions and improved vegetation monitoring through a de-coupling of the canopy background signal and a reduction in atmosphere influences.
The index is given as: = (+) (+ +) where L is a canopy background adjustment factor. An L value of 0.5 in reflectance space was found to minimize soil brightness variations and eliminate the need for additional calibration for different soils. The transformation was found to nearly eliminate soil-induced variations in vegetation indices. [1]
Visual or digital interpretation of the output image/raster created is similar to NDVI: -1 to 0 - Bright surface with no vegetation or water content +1 - represent water content; For the second variant of the NDWI, another threshold can also be found in [20] that avoids creating false alarms in urban areas: < 0.3 - Non-water >= 0.3 - Water.