5.1 - Definitions
Although the names of these variables might be self-descriptive, we should pay attention to their physical definitions:
5.1.1 - Fraction of Vegetation Cover (FVC)
The FVC accounts for the amount of vegetation distributed on a flat background. For a pixel such as that on the next figure, FVC = 24% would tell us the fraction of the total pixel that is covered by green vegetation.
(adapted from Pixabay by Pok Rie)
MAIN APPLICATIONS:
FVC is relevant for agriculture and forestry, environmental management and land use, hydrology, natural hazards monitoring and management, vegetation-soil dynamics monitoring, drought conditions and fire scar extent. (Fraction of Vegetation Cover Product User Manual (PUM)).
5.1.2 - Leaf Area Index (LAI)
LAI [m2/m2] is geometrically defined as the total one-sided area of photosynthetic tissue per unit of ground surface area. It represents the amount of leaf material in ecosystems and controls the links between biosphere and atmosphere through various processes such as photosynthesis, respiration, transpiration and rain interception.
Monitoring the distribution and changes of LAI is important for assessing growth and vigour of vegetation on the planet. It is fundamentally important as a parameter in land-surface processes and parameterizations in climate models.
MAIN APPLICATIONS:
LAI is a key parameter in Numerical Weather Prediction (NWP) models, regional and global climate modelling, weather forecasting and global change monitoring. Monitoring the distribution and changes of LAI is important for assessing growth and vigour of vegetation on the planet. (Leaf Area Index Product User Manual (PUM)).
FVC and LAI are important structural properties of land surface areas occupied by plant canopies, which yield complementary information to describe the three-dimensional structure of the vegetation attributes.
5.1.3 - Fraction of photosynthetically active radiation (fAPAR)
fAPAR represents the fraction of incoming solar radiation in the photosynthetically active radiation (PAR) spectral range (0.4 - 0.7 μm) that is absorbed by the green parts of the canopy.
MAIN APPLICATIONS:
fAPAR has been recognized as one of the fundamental terrestrial state variables in the context of the global change sciences (Steering Committee for GCOS, 2003; Gobron et al., 2006). It is a key variable in models of vegetation primary productivity and, more generally, in carbon cycle models implementing up-to-date land surfaces process schemes (e.g., Sellers et al., 1997). Besides, it is an indicator of the health of vegetation (Fraction of Absorbed Photosynthetic Active Radiation Product User Manual (PUM)).
Seasonal variations in LAI and fAPAR are vital to determine landscape water, energy and carbon balances, as well as in the detection of long-term climate change (Potter et al, 1993, Churkina and Running 1998, cited by Huemmrich et al, 2005).
FVC, LAI and fAPAR are currently estimated from SEVIRI on board MSG (METEOSAT SECOND GENERATION), within the framework of the LSA SAF. The LSA SAF is part of the EUMETSAT SAF Network.
VEGETATION PRODUCTS FROM OTHER SATELLITE PROGRAMS:
The following programs have also implemented algorithms in their operational lines to provide advanced biophysical products:
- POLDER (Leroy et al. 1997, Roujean and Lacaze 2002);
- MODIS and MISR (Knyazikhin et al. 1999);
- MERIS (Gobron et al. 1999, Bacour et al. 2006, Baret et al. 2007);
- SEAWIFS (Gobron et al. 2001);
- VEGETATION (Baret et al. 2007, Bartholomé et al. 2006);
- GLOBCARBON (Plummer et al. 2006, Deng et al. 2006)