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4 - RESULTS MAC EUROPE 1991 
Results of a case study for sugar beet will be presented. 
4.1 Measurements of Leaf Optical Properties 
During July and August 1991 the optical properties of individual sugar beet leaves, measured in the laboratory, 
were rather constant. The measurements yielded for a NIR wavelength (at 870 nm) an average reflectance of 
46.0% and an average transmittance of 48.4%. These values were respectively 7.3% and 0.6% for a red (at 670 
nm) and 15.8% and 13.8% for a green wavelength (at 550 nm). The average scattering coefficient was 0.144 
for the whole PAR region. 
4.2 Estimating LAI and LAD 
Information on both LAI and LAD was obtained by means of the CAESAR scanner in dual look mode. As explained 
in figure 2, measured WDVI values at an oblique and nadir viewing angle plotted into such a nomogram, based 
on the actual recording geometry and the leaf optical properties from section 4.1, can yield estimates of both 
LAI and LAD. Figure 4 gives the results of July 4th for the CAESAR scanner together with simulated curves 
for a spherical, uniform and planophile LAD (LADs as defined by Verhoef & Bunnik, 1981). In this figure more 
realistic LADs are shown as opposed to figure 2 with LADs consisting of just one angle. Results showed that 
sugar beet matched the curve for a uniform LAD rather well, except for the beginning of the growing season 
(LAI< 1.5) when the LAD was more planophile. This information is important for determining the relationship 
between WDVI and LAI. It can also be used to derive extinction coefficients that are input for crop growth models. 
Figure 4. Relationship between the WDVIfrom nadir and the WDVI at an oblique viewing angle of '52°. Simulations 
are for a spherical, uniform and planophile LAD (SAIL model with a hot spot size-parameter of 0.5 for sugar 
beet) and measurements obtained with CAESAR, July 4th - calendar day 185 -, 1991 (13.30 GMT). Solar zenith 
angle is 36° and azimuth angle between plane of observation and sun is 7. 
4.3 Estimating Leaf Optical Properties 
Figure 3 illustrated the influence of LAI and leaf chlorophyll content on the position of the red edge and the WDVI 
as simulated with a combined PROSPECT-SAIL model. By plotting both the measured WDVI and the red edge 
values (both acquired with AVIRIS) into such a nomogram for actual recording conditions, an estimate of both 
LAI and leaf chlorophyll content is obtained (see figure 3). Results for sugar beet yielded an estimated chlorophyll 
content of about 30 pg.cm' 2 , except for the beginning of the growing season (LAI< 1.5) when the chlorophyll 
content was somewhat higher. By using the PROSPECT model this leaf chlorophyll content yielded an average 
leaf scattering coefficient in the PAR region of 0.158. This value is comparable to the one found in section 4.1. 
4.4 Results Calibration SUCROS 
The crop growth model SUCROS was run to estimate the final beet yield for ten selected fanners in the test area. 
Input for the model were the location parameters, weather data for the 1991 growing season and crop-specific