1. LAI/ fAPAR

2. definitions: see: MOD15 Running et al. LAI - one-sided leaf area per unit area of ground - dimensionless fAPAR - fraction of PAR (SW radiation waveband used by vegetation) absorbed - proportion

3. LAI  direct quantification of amount of (green) vegetation  structural quantity  uses:  radiation interception (fAPAR)  evapo-transpiration (H 2 0)  photosynthesis (CO 2 )  respiration  leaf litter-fall

4. LAI  full canopy structural definition (e.g. for RS) requires  leaf angle distribution (LAD)  clumping  canopy height  macrostructure shape

5. LAI  preferable to fAPAR/NPP (fixed CO 2 ) as LAI relates to standing biomass  includes standing biomass (e.g. evergreen forest)  can relate to NPP  can relate to site H 2 0 availability (link to ET)

7. fAPAR  radiometric quantity  more directly related to remote sensing  e.g. relationship to RVI, NDVI  uses:  estimation of primary production / photosynthetic activity  e.g. radiation interception in crop models  monitoring, yield  e.g. carbon studies  close relationship with LAI  LAI more physically-meaningful measure

8. Issues  empirical relationship to VIs can be formed  but depends on LAD, leaf properties (Chl., structure)  need to make relationship depend on land cover  relationship with VIs can vary with external factors, tho’ effects of many can be minimised

10. Estimation of LAI/fAPAR  initial field experiments on crops/grass  correlation of VIs - LAI  developed to airborne and satellite  global scale - complexity of natural structures

11. Estimation of LAI/fAPAR  canopies with different LAI can have same VI  effects of clumping/structure  can attempt different relationships dept. on cover class  can use fuller range of spectral/directional information in BRDF model  fAPAR related to LAI  varies with structure  can define through  clump leaf area  ground cover

12. Estimation of LAI/fAPAR  fAPAR relationship to VIs typically simpler  linear with assymptote at LAI 6 need to define different relationships for different cover types

13. MODIS LAI/fAPAR algorithm  RT model-based  define 6 cover types (biomes) based on RT (structure) considerations  grasses & cereals  shrubs  broadleaf crops  savanna  broadleaf forest  needle forest

14. MODIS LAI/fAPAR algorithm  have different VI-parameter relationships  can make assumptions within cover types  e.g., erectophile LAD for grasses/cereals  e.g., layered canopy for savanna  use 1-D and 3D numerical RT models (Myneni) to forward-model for range of LAI  result in LUT of reflectance as fn. of view/illumination angles and wavelength  LUT ~ 64MB for 6 biomes

19. Method  preselect cover types (algorithm)  minimise RMSE as fn. of LAI between observations and appropriate models  if RMSE small enough, fAPAR / LAI output  backup algorithm if RMSE high - VI-based