The service provides vegetation health early warning. It makes use of a set of qualitative indicators and biophysical variables providing information on the status of vegetation with high temporal frequency over wide areas (country/ continental level) at medium spatial resolution. The indicators described represent the state-of-the-art, exploiting most advanced algorithms and taking advantage of the performance and characteristics of recent optical satellite sensors. 1. VPI (Vegetation Productivity Indicator) Its purpose is to identify drought affected areas. The VPI is used to qualitatively identify areas with potentially low agricultural productivity as compared to what can be expected based on the historical range. It’s derived from a statistical analysis and gives probability ranges (categories) and can be calculated on the basis of either NDVI, fAPAR or DMP (see description below). 2. NDVI (Normalized Difference Vegetation Index) NDVI measures the relative presence (or absence) of healthy, green vegetation, exploiting spectral features in optical data. Over the course of a growing season, we first see a steady increase in the ‘vegetation health and density’ values as the young, green vegetation grows (the growth makes the surface appear more and more green). This increase reaches a maximum value just before it drops suddenly at harvest time or when the plants die naturally. 3. fAPAR (fraction of Absorbed Photosynthetically Active Radiation) The solar radiation reaching the surface in the 0.4-0.7 μm spectral region is known as the Photosynthetically Active radiation (PAR). fAPAR refers to the fraction of PAR that is absorbed by a vegetation canopy: it is a primary variable controlling the photosynthetic activity of plants, and therefore constitutes an indicator of the presence and productivity of agricultural, forest and natural ecosystems, as well as of the intensity of the terrestrial carbon sink. fAPAR estimates result from the analysis of multiple measurements with the help of a radiation transfer model in plant canopies using remote sensing observations as constraints. In parallel to the optical indicators, the service provides soil moisture indicators for the start of the growing season (showing water availability to vegetation) as well as for monitoring drought and/or wet spells. These indicators are completely independent from the optical ones and as such work as a cross-validation source. Information on the start date and progress of the growing season can be derived from these indicators, as well as derived products such as early estimates of crop yields and drought indices. |