191 
vegetation 
t cases, the 
ilated using 
in accuracy 
nation. For 
iwever, our 
1 this study , 
2 structural 
il variables 
1 to similar 
that it was 
description 
it lead also 
to develop 
e the effect 
ome of the 
itents were 
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opy model 
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(fared that 
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: minimum 
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nal use of 
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lost of the 
irmation is 
iis type of 
jvelopment 
of biological models. The second problem is relative to the choice of the approach to be used. From these 
preliminary results, it seems that inverting physical radiative transfer models did not necessarilly provide very 
accurate estimates of canopy biophysical parameters. A compromise has to be investigated in between the 
realism of the model that generally induces more complexity and more parameters, and the invertibility that 
most oftenly requires a simplified model with very few variables to be estimated. Presumably, an alternative 
approach would necessitates some a priori knowledge on the target, such as the specy, the type of soils, all kind 
of information that could be derived partly from remote sensing and used to constrained the inversion process. 
ACKNOWLEDGEMENTS 
We are indebted to Dr. Kuusk for the improvement of the Fortran code of the SAIL model in 
order to take into account the hot spot effect. Many thanks to J. Clark, J. Eastwood, J.F. Hanocq, T. Malthus, 
andM. Steven for their support during the field experiments. 
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