Produced by: FastOpt
The Leaf Area Index (LAI) and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) product is produced using a Two Stream Inversion Package (TIP) method applied to visible (VIS) and near infrared (NIR) broadband albedos (from the QA4ECV albedo product).
The definitions of LAI and FAPAR used in this product are as follows:
- LAI – Half the total canopy area per unit ground area (m2 / m2) for a homogeneous canopy of infinitesimally small Lambertian surfaces, akin to a turbid medium.
- FAPAR – The simulated absorption of the photosynthetically active radiation (estimated for the visible band) by a homogeneous canopy of infinitesimally small Lambertian surfaces, akin to a turbid medium.
The TIP is based on the Two-stream Model developed by Pinty et al. (2006) (source code along with further information is available at JRC), which implements the two-stream approximation of radiative transfer for a homogeneous canopy (“1D-canopy”). The 1D radiative transfer model is consistent with large-scale climate and Earth system models and does not require assumptions about other factors (e.g. biome type) to be made. Owing to the 1-D approach, TIP-LAI is an effective quantity.
For efficient processing, the retrievals are taken from Look Up Tables (LUTs), generated with the TIP. In the implementation described here (product_id – “TIP-QA4ECV”, tiptable_version = “V1.3”) it allows for the retrieval of effective LAI and FAPAR and their uncertainties from Top-of-Canopy (TOC) VIS and NIR Bi-hemispherical Reflectances (BHRs) and their joint variance-covariance matrix. By using the full variance-covariance matrix of the BHRs, it is an enhancement beyond previous implementation of the TIP (Disney et al. 2013; Lavergne et al. 2006; Muller et al. 2013).
Based on the global albedo data on 0.5 degree and 0.05 degree regular grids, TIP-LAI and TIP-FAPAR are available for 1982 to 2016.