1106 
more sensitive to a than either of the other indices, but that its sensibility to soils makes it essentially useless for 
estimating this parameter, because most values of the index correspond to a wide range of c, depending on the 
soil type. Conversely, the other indices are somewhat less sensitive to a, but their much reduced sensitivity to 
soil type make them definitely better indices to evaluate this parameter. 
Parameters 
Value 
Table 1 : Vegetation parameters used in 
Foliar chlorophyll concentration (jJ.gcm'2) 
40.0 
the model simulation 
Foliar water content (mm) 
0.2 
Foliar structural parameter (N) 
2 
Leaf inclination distribution parameter (%1) 
0.0 
Solar zenith angle (°) 
30.0 
.4ii 
f° 
o 0. 
1 °.: 
£ 
-t 0.: 
§ 
z0.2$ 
0. 
0 
0. 
0.04 
).a. 
1 . 1 ! i 
’St 4 
10 
x 
BRIGHT SOILS 
7 X ® 
6x X X 8 
MEDIUM SOILS 
DARK SOILS 
02 0.3 
Red reflectance 
0.4 
Figure 1: Red and near-infrared reflectances 
for the 10 soils. The original spectra compiled by 
Bowker et al., (1985) were convolved with the AVHRR 
spectral bands. 
Figure 3: Variability of the values of various vegetation 
indices over 10 bare soils classified by soil brightness 
from dark to bright 
Figure2 Isolines of red and near-infrared 
reflectances for a synthetic canopy over 10 soil 
types as a function of the fractional vegetation 
cover. 
Figure 4: Minimum and maximum values for the 
five vegetation indices as a function of fractional 
vegetation cover, for the set of 10 soils.