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5. COMPARISON BETWEEN SIMULATIONS AND DATA MEASUREMENTS 
In 1989, a campaign of measurements was conducted on an agricultural watershed (Orgeval, France) to 
study the problem radar response over natural surfaces. All data used in this section are from this 
campaign [5]. 
During this campaign the ERASME radar acquired data along 14 cross-paths of 3 Kin, and measurements 
of all soils parameters (humidity, height profiles) were done at die same time. 
ERASME is a French airborne scatterometer, operating at C and X band (5.35 and 9.65 GHz) with HH 
and VV polarisation. Its forward looking configuration and its large elevation beam width (±10° at 3dB) 
allow the observation of the same target with a large incident angle during a single flight. 
7 fields were selected for the present study. 3 fields correspond to an isotropic surface on which the row 
structure is not marked (P1,P2,PL). The description of each field is described in the table 1. 
Field Name 
type of cultivation 
Cl C2 C3 
Com sowing fields 
F 
Flax sowing field 
PI P2 
Pea fields 
(smooth surface) 
PL 
Ploughed field 
(very rough) 
table 1 
The surface parameters of these experimental fields are given in the table 2 
Surface parameters (cm) 
C-Band (5.35 GHz) 
X-Band (9.65 GHz) 
Field 
name 
s 
1 
S 
L 
P 
ks 
kl 
Dielectric 
constant 
ks 
kl 
Dielectric 
constant 
Cl 
1.32 
4.54 
1.64 
34.0 
46.0 
1.48 
5.09 
9.26 
-1.34 
2.67 
9.18 
6.90 
-1.85 
C2 
1.29 
3.77 
1.16 
22.3 
54.0 
1.45 
4.22 
12.3 
-1.97 
2.61 
7.62 
10.0 
-2.99 
C3 
1.33 
6.43 
0.61 
15.9 
23.0 
1.49 
7.20 
9.57 
-1.40 
2.69 
13.0 
7.18 
-1.95 
F 
0.84 
4.94 
0.42 
57.9 
25.0 
0.94 
5.54 
11.1 
-1.72 
1.70 
9.98 
8.72 
-2.52 
PI 
1.49 
5.88 
- 
- 
- 
1.67 
6.59 
16.1 
-2.76 
3.01 
11.9 
14.8 
-4.64 
P2 
0.80 
4.21 
- 
- 
- 
0.90 
4.72 
11.5 
-1.80 
1.62 
8.51 
9.15 
-2.68 
PL 
2.83 
9.17 
- 
- 
- 
3.17 
10.3 
13.6 
-2.23 
5.72 
18.5 
11.5 
-3.52 
table 2 
About the comparison between radar measurements and IEM simulation, we notice that the simulations 
tend to overestimate the absolute level of the back scattering coefficient (o°). In these simulations we 
focus on the o° variation with the incidence angle. 
The following simulations are classified according to the type of the surface. 
- On very rough surface without a row structure: Ploughed field (PL) 
The simulations given by the IEM model show a fiat variation of o° versus incidence angle (only 
Ao°=3dB for A0=3O°). Radar cross section measurement presents a slight dispersion, but the mean slope 
of o° with the incidence angle is the same as on the simulation.