Vegetation Parameters

Vegetation parameters include satellite measurements of leaf area, biomass indicators, leaf duration and net primary productivity. Together these products provide fundamental inputs to parameterize or validate ecosystem process models and help the scientific community understand the dynamics of these important global elements.

Vegetation Indices

A vegetation index broadly defines the mathematical expression of spectral bands sensitive to chlorophyll absorption and cell wall reflectance. These expressions, usually in the form of ratios of individual bands or sums or differences of bands, are useful in quantifying the amount of vegetation, as biomass, involved in a signal’s response. Vegetation Indices include Normalized Difference Vegetation Index (NDVI) (Steven et al. 1983), Enhanced Vegetation Index (EVI) (Huete et al. 2002), Soil Adjusted Vegetation Index (SAVI) (Huete 1988), and other derived products.

More information can be found in the Vegetation Index ESDR white paper.

Leaf Area Index (LAI) / Fraction of Photosynthetically Active Radiation (fPAR)

LAI defines an important structural property of a plant canopy as half the total developed area of green (i.e. photosynthetic active) leaves per unit ground horizontal area (Chen and Black 1992). fPAR measures the proportion of available radiation in the photosynthetically active wavelengths (400 to 700 nm) that a canopy absorbs. LAI and fPAR are biophysical variables which describe canopy structure and are related to functional process rates of energy and mass exchange. Both LAI and fPAR have been used extensively as satellite derived parameters for calculation of surface photosynthesis, evapotranspiration, and annual net primary production. These products are essential in calculating terrestrial energy, carbon, water cycle processes, and biogeochemistry of vegetation.

More information can be found in the LAI/fPAR ESDR white paper.

Gross Primary Productivity (GPP) / Net Primary Productivity (NPP)

The rate at which light energy is converted to plant biomass is termed primary productivity. Gross Primary Productivity (GPP) is the initial daily total photosynthesis, and daily net photosynthesis subtracts leaf and fine-root respiration over a 24-hour day. Net Primary Productivity (NPP) is the annual sum of daily net photosynthesis minus the cost of growth and maintenance of living cells in permanent woody tissue (Running et al. 2004).

More information can be found in the GPP and NPP ESDR white paper.

Phenology

Land surface phenology is defined as the seasonal pattern of variation in vegetated land surfaces observed from remote sensing. While the observed patterns are related to biological phenomena, land surface phenology is distinct from traditional definitions of vegetation phenology, which refer to specific life cycle events such as budbreak, flowering, or leaf senescence using in-situ observations of individual plants or species. Land surface phenology provides aggregate information at moderate (500-m) to coarse (25-km) spatial resolutions that relates to the timing of vegetation growth, senescence, and dormancy and associated surficial phenomena at seasonal and inter annual time scales.

More information can be found in the Phenology ESDR white paper.