615 
Chattier M., P. Bonchretien, P. AJlirand, G. Gosse, 1989, 'Utilisation des cellules au silicium amorphe pour la mesure 
du rayonnement photosynthetiquement actif, Agronomie, 9, 281-284. 
Choudhury B.J., 1987, 'Relationships between vegetation indices, radiation absorption, and net photosynthesis 
evaluated by a sensitivity analysis', Remote Sensing of Environment, 22, 209-233. 
Goutorbe et al., 1993, 'HAPEX-Sahel: A large scale study of land-atmosphere interactions in the semi-arid tropics', 
Annales Geophysicae, submitted. 
Goward S.N. and K.F. Huemmrich, 1992, 'Vegetation canopy PAR absorptance and the normalized difference 
vegetation index: An assessment using the SAIL model’, Remote Sensing of Environment, 39, 119-140. 
Monteith J.L, 1972, 'Solar radiation and productivity in tropical ecosystems', Journal of Applied Ecology, 9, 747-766. 
Prince et al., 1993, 'Geophysical, biological and remote sensing aspects of the Hydrologic Atmospheric Pilot 
Experiment in the Sahel (HAPEX-Sahel), Annales Geophysicae, submitted. 
Sellers PJ., 1987, 'Canopy reflectance, photosynthesis and transpiration. II. The role of biophysics in the linearity of 
their interdependence', Remote Sensing of Environment, 21, 143-183. 
van Leeuven W., A.R. Huete, J. Duncan, and J. Franklin, 1993, 'Radiative transfer in shrub savanna sites in Niger - 
Preliminary results from HAPEX-Sahel: III. Optical dynamics and vegetation index sensitivity to biomass and plant 
cover ', Agricultural and Forest Meteorology, submitted. 
Verhoef W., 1984, 'Light scattering by leaf layers with application to canopy reflectance modeling: the SAIL model', 
Remote Sensing of Environment, 16, 125-141. 
Sub-sites 
Bush/Grassiand 
Grassland 
Degraded Bushiand 
Millet field 
Sampled plot area (m 2 ) 
100 
100 
100 
100 
Number of sensors’ 
100 
60 
120 
SO 
" Detectors on the ground measuring transmitted radiation. 
Table 1: Sampled plots over the 4 sites on the West Central super site. 
LAI m „- 
(date) 
WAI 
Density 
(clumps/ha) 
Height 
(m) 
Radius 
(m) 
Vegetation cover 
(clumps) 
Plot grassland 
1.40 (300) 
Site grassland 
1.40 (300) 
Plot bushiand 
- Guiera 
0.13 (300) 
0.013 
800 
0.89 
0.49 
6.0% 
• Herb 
0.00 
Site bushiand 
- Guiera 
0.25 (300) 
0.017 
314 
1.42 
0.80 
6.3% 
• Herb 
0.99 (254) 
Plot bush/grassiand 
- Guiera 
1.14 (300) 
0.100 
800 
2.07 
1.18 
35.0% 
- Herb 
1.21(300) 
Site bush/grassiand 
- Guiera 
0.32 (300) 
0.026 
477 
1.53 
0.83 
10.3% 
- Herb 
1.03 (300) 
Plot millet 
0.51 (260) 
. 
4400 
1.18 (269) 
0.24 (252) 
8.0% 
Site millet 
0.28 (260) 
3600 
1.18 (269) 
0.24 (252) 
6.5% 
~ Green LAI if date < 300, total LAI if date=300. 
Table 2: Vegetation morphology of the plots and sites.