Calculations, a computer's
As the fAPAR is directly proportional to the NVDI, it can be simply
calculated from the NDVI values. In other words, an NDVI image can
be converted into an fAPAR image paler tones= higher fAPAR). Another
crop parameter can also be calculated via the NDVI, namely the LAI
or Leaf Area Index (leaf surface area per surface area of soil).
Both the LAI and fAPAR can be used to make a quantitative estimate
of agricultural production. There are several ways of doing this.
One way is to take historical data as the basis and then check for
the statistical link between the cumulative fAPAR satellite (or
LAI) data and the harvest. Alternatively, the satellite data can
be introduced into a crop growth model. In this way, the LAI or
fAPAR which in a model are normally calculated on the basis of meteorological
data, can be replaced by satellite measurements. This has the major
benefit of no longer being dependent on spot measurements. Meteorological
data are linked to a measuring station, which means that for other
locations estimates must be made on the basis of these spot values.
Satellite data on the other hand always provide pixel-specific information.