1CWHEAT2 simulation 
ves, 77 Tillers 2 with 8 
are obtained for Tillers 
on, the complete leaf is 
senescent parts, which 
ime, the area tested for 
but 679 leaf elements 
are turned down, as it 
:ent at this period and 
te radiosity equations 
i 5c correspond to the 
l angle, and y is the 
regarding the chosen 
a they are numerous, 
ig each others, which 
bserved on figure 6, 
Figure 6: Bidirectional visible reflectances over the canopy described in 2 J 2) in the principal plane: red (—), 
blue (- ■). and green ( - ). Sun zenith angle is 30 degres. Green is die lower one due to greater soil 
contribution, which is a result of the canopy architecture description, as explained in the text. 
4-CONCLUSION 
We have tried to apply the radiodity method on a wheat canopy whose architecture is described in part by a crop 
production model. This first test indicates that it is possible. Results show that this method is very interesting to 
correctly retrieve the main features of the bidirectional reflectance, it means especially the hot spot effect in the 
principal plane. However, the complete and correct description of die structure of such a canopy has not been yet 
correctly achieved in this study. Clearly, the first objective of the canopy development submodel in 
AFRCWHEAT2 is to simulate useful information for the yield estimation, and we must take into account specific 
works regarding the temporal changes in the structure of a canopy to improve the description which we need in 
order to be more confident in our computation of the view factors. Following improvements would be to consider 
that the individual elements are not Lambertian, and the association of elements to define objects would allow to 
work with a more important number of leaves. 
ACKNOWLEDGEMENTS 
The authors thank J.Porter for providing the original AFRCWHEAT2 code. 
references 
Hotel C.C., Gersl S.A.W., and Powers BJ„ 1991. The Radiosity Method in Optical Remote Sensing of 
Structured 3-D Surfaces. Remote Sens. Environ. 36:13-44. 
Gersd SA W. and Borel C.C., 1990. Principles of the radiosity method for canopy reflectance modeling Proc 
IGARSS’90 Vol.3, pp 1735-1737. 
(red). Illuminations