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savanna is a consequence of a strict cloud detection. Based upon 
these comparisons, it is difficult to say which product is the best 
over sites where large differences are observed. 
The last step of the POLDER-2 validation will be the 
comparison of LAI and FVC to the reference products 
generated from the ground measurements collected by the 
VALERI (VAlidation of Land European Remote Sensing 
Instrument) project (www2). From April to October 2003, 6 
sites were instrumented around the world. The data are still 
under processing. 
4. CONCLUSION 
The Level 3 algorithms developed to process the POLDER-2 
data are based upon the inversion of a linear reflectance model 
to estimate directional-hemispherical reflectances and NDVI, 
and upon a neural network inverting a radiative transfer model 
to calculate LAI and FVC. Before these inversions, a filtering 
module scans the bi-directional BRDF and removes the 
contaminated observations. 
Directional coefficients, DHR, NDVI, LAI and FVC are 
generated from Arpil to October 2003. They are validated using 
temporal and spatial criteria of consistency, comparison with 
POLDER-1 products, comparison with concomitant MODIS 
products and, finally comparison with ground measurements. 
Considering the first three steps, the POLDER-2 biophysical 
parameters are relevant to characterize the land surface. The 
spatial distribution and temporal evolution of ecosystems are 
well reproduced, and the values are realistic. Some 
discrepancies appears with MODIS products. Final comparisons 
with concomitant ground measurements from VALERI 
reference products will be soon performed. 
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wwwl: ftp://ersa.bu.edu/pub/rmyneni/myneniproducts/MODIS/ 
Www2: http://www.avignon.inra.fr/valeri/