395 
incidence angles [30°,40°] and [40°,50°], rain increases ct 0 and the intercept B. We can also see the modification 
of slope A. We can not conclude at this level if this modification is the result of changes in soil moisture or if it 
is related to soil flattening by rain. Thus we think that we need to have synchronous ERS1 WSC data and 
rainfall data. To understand the roughness and soil moisture effects on A, a modeling approach is used. 
Figure 5: Temporal evolution of rainfall (o) in mm, o 0 (x) in (db), B(*) in db, A*50(+) in db/dg for [30°,40°] and [40°,50 0 ]. 
Scaling factor of rainfall: -rain/3. 
6.2. WSC/Soil moisture : Some authors [11] have shown that to increase the sensitivity of ct 0 to soil 
moisture, it is advised to work in the incidence angles range from 7° to 17°, and at frequencies about 5Ghz. For 
this reason, we have compared the temporal evolution of a 0 at low incidence angles (18 and 21°) with soil 
moisture measurements (0-5cm deep). 
Figure 6 : Temporal evolution of volumetric soil moisture (*) and O 0 (x) in db from 18 to 21°. 
As we can see on figure 6, the two curves are very similar up to doy (day of year) 242 (August 29). After that 
date, two factors might explain the difference: first betwen doy 242 and 252 we did not have WSC Hat« to 
monitor the rapid evolution seen in soil moisture, then vegetation cover is significant (see figure 1) and reduce 
CT o sensitivity to soil moisture [11]. However, for a more accurate soil moisture retrieval this effect must be 
taken into account. 
63. Synergism with AVHRR data : In this part, we have considered two sets of ERS1 WSC data 
[30°,40°] and [40°,50°] acquired with mid beam antenna. AVHRR data is presented by MSAVI.