Physically based methodology for generating LAI and FPAR earth system data records from AVHRR and MODIS

We have developed and tested a physically based approach, rooted in the theory of stochastic radiative transfer within vegetation, for generating a seamless time series of LAI and FPAR fields from AVHRR NDVI data and MODIS reflectance data. Our goal is to: (i) develop a theoretical formulation that results in consistent LAI and FPAR fields from satellite data of varying spectral and spatial resolutions, and (ii) assess the uncertainties in the generated fields due to differences in quality and information content of AVHRR and MODIS sensors. Our results suggests that single scattering albedo and overall relative uncertainty of input surface reflectances and/ or NDVI are configurable parameters in governing the accuracy of LAI/FPAR retrievals from NDVI as an input. Single scattering albedo accounts for differences in both spatial and spectral resolution and the implementation of the algorithm is performed over test areas such that: (i) the consistency requirements are met, (ii) the retrieval index is maximized, and (iii) the difference between reference LAI and LAI obtained from AVHRR NDVI is minimized.