4.2 - EVI

The Enhanced Vegetation Index was developed by the MODIS Science Team to take full advantages of the sensor capabilities. In order to increase thesensitivity to the vegetation signal, the index makes use of measurements in the red and near infrared bands (as in the case od NDVI), and also in the visible blue band, which allows for an extra correction of aerosol scattering. EVI also performs better than NDVI over high biomass areas, since it does not saturate as easily.

EVI_equation

Where ρ are atmospherically corrected or partially corrected (Rayleigh and ozone absorption) reflectances, L is the canopy background adjustment,C1 and C2 are coefficients related to aerosol correction and G is a gain factor. The blue band is used to remove residual atmosphere contamination caused by smoke and sub-pixel thin clouds

figure1_42

Figure 4.2.MODIS/Terra Vegetation EVI 16-Day L3 Global 250m SIN Grid.
(extracted from https://lpdaac.usgs.gov/lpdaac/products/modis_products_table/, accessed in 2010)

EVI main advantages and disadvantages.

Advantages:

  • Found to perform well under high aerosol loads , biomass burning conditions (Huete et al., 2002)

Disadvantages:

  • Inherent nonlinearity because it is a ratio based index
  • To compensate for the effects of NDVI saturation over high biomass areas, EVI tends to present relatively low values in all biomes and also lower ranges over semiarid sites.
  • The correction for aerosol impact on the final index makes use of reflectances measurements within VIS blue, not always available (the case of AVHRR or SEVIRI sensors).
  • Is not a structural property of a land surface areas