Improving the retrieval of key biophysical parameters used in climate modeling from POLDER hot spot measurements

A practical approach is presented for deriving global maps of biophysical parameters which are primarily useful for meteorological and climate modeling. These parameters are albedo, LAI, vegetation fractional cover, and absorbed PAR. The algorithm for albedo has already been implemented successfully in POLDER data processing chain. The reliability of the method for other parameters needs to be assessed. It combines the use of spectral and directional vegetation indices. An example of application is shown for global POLDER LAI and the quality of results is demonstrated through a comparison with ground measurements over a large set of different vegetation types. The up-scaling issue is addressed empirically in adjusting clumping indices which is highly required for the major biomes of boreal and tropical forests. It is finally discussed on the added value of POLDER observations thanks to a measurement of the hot spot, thereby contributing to retrieve the clumping index on a physically basis as well as improving the albedo calculation