Figure 1 - POLDER image of the total radiance at 850 nm on June 21th over Camargue. 
2.2 Photopolarimetric measurements of the surface 
Extensive descriptions of the instrument are given in Herman et al, 1986, Deuze et al, 1989 and 
Rondeaux and Herman, 1991. The instrument analyses the signal at 550 nm, 650 nm and 790 nm. This 
last wavelength is the upper value allowed by an unique polarizor used to analyse the state of the 
polarization. The polarizor rotates at a speed of 48 rd/mn, the signal is sampled at 0.01 ms rate and 
analyse with a microprocessor to provide a set of three descriptive parameters for the polarization. A 
scanning mirror is adapted to the instrument to obtain measurements in a vertical plane with an angular 
step of six degrees. The instrument was set up on a roof of a van as shown in figure 2; the FOV is + 6 
degrees which means that the size of the spot has typically a diameter of 50 cm. An extensive archive of 
the properties of the calibration test site of La crau was conducted indicating a weak polarization. These 
measurements are not in our scope here and we reported in table 1 the main characteristics of the data sets 
we did on June 21th in the agricultural site. Table 1 gives for each field the reflectance measured at nadir 
for the three bands as well as the NDVI. 
Table 1 - Field measurements of the bidirectional reflectance and of the degree of polarization for June 
21th. 1991 in Camargue. We reported here the reflectances(in percent) for the three bands plus the NDVI. 
550 nm 
650 nm 
790 nm 
NDVI 
6.1 
8.0 
17.5 
0.370 
wheat 
8.4 
8.3 
23.9 
0.484 
vine + grass 
7.5 
7.2 
15.4 
0.361 
vine 
1.5 
1.6 
3.7 
0.394 
vine 
10.3 
6.5 
71.2 
0.832 
sunflowers 
10.1 
5.6 
65.4 
0.842 
sunflowers 
7.9 
5.7 
40.0 
0.752 
grass 
10.0 
8.3 
29.4 
0.558 
vine 
7.2 
10.0 
18.2 
0.289 
wheat 
8.5 
4.9 
50.0 
0.821 
sunflowers 
10.6 
4.8 
64.4 
0.860 
sunflowers