FPAR
Fraction of Photosynthetically Active Radiation. The fraction of incoming solar radiation in the 400-700nm range that is absorbed by vegetation for photosynthesis. A key input for estimating gross primary productivity and carbon cycling.
Overview
The Fraction of Absorbed Photosynthetically Active Radiation (FPAR) quantifies the proportion of incoming solar radiation (400–700 nm) absorbed by vegetation for photosynthesis. Values range from 0 (bare ground) to ~0.95 (dense canopy). FPAR is a fundamental driver of plant productivity and key input for GPP and NPP models.
How It Works
FPAR is estimated from satellite data using lookup tables from radiative transfer models or empirical relationships with vegetation indices. The MODIS FPAR product (MOD15A2H) uses a 3D radiative transfer model accounting for canopy structure, leaf properties, and soil background. When the main algorithm fails, a backup NDVI-based relationship is used.
Key Facts
- Measures fraction of 400–700 nm radiation absorbed by vegetation.
- MODIS MOD15A2H provides FPAR and LAI together at 500 m, 8-day composites.
- Key input to MOD17 GPP/NPP algorithm for global carbon accounting.
- Designated an Essential Climate Variable by GCOS.
Applications
Global Productivity Estimation
Multiplied by incoming PAR and light-use efficiency to estimate GPP in the MODIS MOD17 algorithm.
Climate Modeling
Earth system models use FPAR to simulate vegetation-atmosphere carbon exchange.
Yield Forecasting
Integrating FPAR over the growing season estimates accumulated biomass and predicts grain yield.
Limitations & Considerations
Sensitive to atmospheric correction errors and cloud contamination. Can overestimate at low-productivity sites. The FPAR-vegetation index relationship is biome-dependent. Snow cover causes anomalously low values in boreal regions.
History & Background
Emerged from Monteith's (1972) light-use efficiency framework. Remote estimation advanced with AVHRR and matured with MODIS (1999). Recognized as an Essential Climate Variable.
Analyze FPAR data with LYRASENSE
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