Figure 5: Experimental "volumetric 
water content /backscattering 
coefficient" relationships 
(5.3 GHz, 15',polarization 
HH). (0), (- ) and ( ) are 
respectively experimental 
results linear and nonlinear 
relationship using 0o-6.(--) 
is the linear realtionship 
using 0o-5 
4.1.2. Roughness effects. Four 
fields were compared using 
configuration I. Their roughness varied 
with a standard deviation of height 
ranging from 0.ÛÛ6 to 0.011 m. In 
Figure 6 each field is represent by 
specific symbol. Because of the low 
number of measurements for each field, 
we did not make a statistical analysis 
of the roughness effect. For the 
studied range of roughness there is no 
apparent effects of the roughness on 
the 00-5/00 relationships. These 
results are in agreement with those 
presented by Ulaby et al., 1978. Note 
that we have tested a small range of 
roughness conditions which could be 
encountered for seed bed implement. 
4.1.3. Soil moisture heterogeneity 
effects. A specific experiment was 
devised in order to answer to the 
following question: Does the 
backscattering coefficient could be 
related to the mean water content when 
a microwave sensor look at 
heterogeneous area. A square field of 
144 m 2 was divided into two triangles 
which differed from each other by the 
water content (00-5= 0.251 m 3 . nr 3 in 
the wet triangle and 00-5= 0.090 m 3 . m* 3 
in the dry one). Backscattering 
coefficients were obtained from 12m 
track. Ten measurements were performed 
with 10 different tracks that cover 
Figure 6: Roughness effects on the 
backscattering coefficient 
(5.3 GHz, 15', polarization 
HH): s=0.011 m (x,+), s=0.010 
m (O), s=0.006 m (*) 
Backscattering coefficient (db) 
different proportions of the wet or dry 
parts of the field. The corresponded 
mean volumetric water contents (00-5) 
were calculated as a function of each 
area proportion of the dry or wet parts 
seen by the instrument. Figure 7 shows 
a linear relationship between the 
backscattering coefficient and 0o-5. 
These results are also included in 
Figure 1. The linearity of the 
relationship presented in Figure 7 and 
the good agreement with results 
Figure 7: Experimental "volumetric 
water content (0- 
5cm)/backscattering 
coefficient" relationship 
(5.3 GHz, 15 .polarization 
HH) obtained on an 
heterogeneous field. Spatial 
mean value of 80-5 is taken 
into account. 
Backscattering coefficient (dB) 
706