Coupling remote sensing observation models and a growth model for improved retrieval of (geo)biophysical information from optical remote sensing data

In the ESA study GeoBIRD (Geo- and Biophysical Information from Remote Sensing Data) the process-based vegetation growth model PROMET-V was coupled to the GeoSAIL, canopy reflectance model for the retrieval of spatially distributed biophysical parameters from surface reflectance images derived from Landsat TM data. The raster based PROMET-V model calculates plant growth, water and nitrogen fluxes using meteorological data, a land use map, and a soil map. In this study the total leaf area index (LAI), the fraction brown leaf area and surface soil moisture, as modelled in PROMET-V, were used in conjunction with GeoSAIL, to model the surface reflectance spectra. Besides modelling the canopy reflectance GeoSAIL, also accounts for the soil reflectance using the dry soil spectrum and surface moisture as inputs. By minimising the difference between observed reflectance spectra derived from LANDSAT images and the modelled surface reflectance spectra, the total LAI, fraction of brown leaves and surface soil moisture were estimated. This optimisation process is constrained by physically and plant physiologically meaningful boundaries in order to obtain valid results and accelerate the process. By re-initialising the PROMET-V model, the retrieved and simulated LAI were matched. This leads to improved model results regarding biomass and yield.