The Leaf Area Index (LAI) is defined as half the total area of photosynthetically active elements (e.g. leaves, needles) of the canopy per unit horizontal ground area. The LAI is a measure of the size of the interface for exchange of energy (including radiation) and mass between the canopy and the atmosphere. The LAI is strongly non-linearly related to reflectance. A satellite-derived LAI value corresponds to the total green LAI of all the canopy layers, including the understory which may represent a very significant contribution, particularly for forests. Practically, one can say that the LAI quantifies the thickness of the vegetation cover. For remote sensing of the LAI it is often assumed that the leaves are randomly distributed within the vegetation volume sensed and hence the retrieved LAI is an "effective" LAI being the best possible approximation of the actual LAI (see also the references).
Top of canopy input reflectance from SPOT-4 & -5 and - more recently - PROBA-V in red, near infrared and shortwave infrared bands, normalized over a period of 30 days are used in a neural network approach. Normalization over the 30-day period us done with a weighting function which favors the most recent daily observations of the compositing period. The neural network is trained with true (non-simulated) reflectance data and LAI estimates from fused existing products based on MODIS and CYCLOPES LAI products. Note that "clumping" or "clumpiness" (see Chen et al., 2005), i.e. the degree with which the leaves are not randomly distributed within the vegetation volume sensed, is not part of the data set offered here.
For more information we refer to the ATBDs mentioned in the references section.
This is version 1 of this data set provided by COPERNICUS Global Land Service, downloaded from the data server at VITO in July 2016.
Data were downloaded in hdf5 file format with 1/112° grid cell resolution, organized in tiles of 10° latitude x 10° longitude. Data were block-averaged onto a 0.5° x 0.5° plate carree grid. Data are available for the latitude range 70°S to 80°N. Note, however, that limited solar illumination reduces the maximum northern latitude to smaller values during winter.
This data set has been put into our data base in August 2016.