OLCI Global Vegetation index
OLCI Global Vegetation Index
Before computing the OLCI Global Vegetation Index (OGVI), a spectral test is performed on every land pixel to flag any pixels that are not vegetated. On vegetated pixels, the OGVI is estimated in two steps.
The information contained in the blue band at 443 nm is combined with the information in the bands at 681 and 865 nm, traditionally used to monitor vegetation, to generate "rectified channels" at these latter two wavelengths. The "rectification" is performed in such a way as to minimise the difference between those rectified channels and the spectral reflectance that would be measured at the top of the canopy under a standard geometry of illumination and observation. The proposed algorithm assumes that ratios of polynomials are appropriate to generate both the "rectified channels" and the final spectral index (OGVI).
The OGVI has been optimised to assess the presence on the ground of healthy, live, green vegetation. The optimisation procedure has been constrained to provide an estimate of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) in the plant canopy, although the index is expected to be used in a wide range of applications.