Vegetation variables (Postel)
The “continental vegetation and soils” biogeophysical products of Postel are spatialized variables derived from optical or micro-wave sensors measurements acquired over many years at regional to global scales
Leaf Area Index (LAI)
The leaf area index (LAI) is defined as half the total foliage area per unit of ground surface (Chen and Black, 1992). It is assessed using various approaches and algorithms applied to many sensors data (Vegetation, Polder, Modis, AVHRR) in the frame of the Amma project.
Fraction of Vegetation Cover (FCover)
The fraction of vegetation cover (FCover) is the fraction of ground surface covered by vegetation. Fcover is assessed using various approaches and algorithms applied to Vegetation, and Polder, data in the frame of the Cyclopes project.
Fraction of Absorded PAR (FAPAR)
The fraction of absorded PAR (FAPAR) is defined as the fraction of photosynthetically active radiation absorbed by vegetation for photosynthesis activity. The FAPAR can be instantaneous or daily. FAPAR is assessed using various approaches and algorithms applied to many sensors (Vegetation, Polder, Modis, AVHRR) in the frame of Polder and Amma projects.
Normalized Difference Vegetation Index (NDVI)
The Normalized Difference Vegetation Index (NDVI) is calculated as the normalized ratio of the difference between the reflectances measured in the red and near-infrared sensor bands. The NDVI is the most frequently used vegetation index to assess the quantity of vegetation on the surface, and to monitor the temporal ecosystems variations. Postel provides NDVI, derived from observations of various sensors (Polder, AVHRR, Seviri) in the frame of different projects : Polder – Parasol and Amma.
Land Surface Reflectance
The surface reflectance is defined as the part of solar radiation reflected by the land surface. The measured surface reflectance depends on the sun zenith angle and on the viewing angular configuration. Consequently, two successive measurements of the surface reflectance cannot be directly compared. Therefore, the directional effects have to be removed using a normalization algorithm before generating a composite. The surface reflectance is provided in the frame of projects: Cyclopes, Geoland and Globcover.
Chen, J. M. and T. A. Black, Defining leaf area index for non-flat leaves, Plant, Cell and Environment, 15, 421-429, 1992.