Current emphasis in the EOS era involves operational 'external' noise removal through improved calibration, atmospheric correction and standardization of sun-surface-sensor geometries with bidirectional reflectance distribution function (BRDF) models. The enhanced vegetation index (EVI) was developed to optimize the vegetation signal with improved sensitivity in high biomass regions and improved vegetation monitoring while correcting for canopy background signals reducing atmosphere influences. The equation takes the form,

where r are atmospherically-corrected or partially atmosphere corrected (Rayleigh and ozone absorption) surface reflectances, L is the canopy background adjustment term, and C1 , C2 are the coefficients of the aerosol resistance term, which uses the blue band to correct for aerosol influences in the red band. The coefficients adopted in the EVI algorithm are, L=1, C1 = 6, C2 = 7.5, and G (gain factor) = 2.5.

Source: http://tbrs.arizona.edu/cdrom/VI_Intro/VI_MOD_VI.html