5. CONCLUSIONS 
708 
Accurate estimations of soil moisture 
can be derived from C band 
backscattering measurements using the 
optimal configuration But this result 
was obtained in environmental 
controlled conditions : 
(1) only one soil texture was studied, 
(2) roughness surface was relatively 
smooth and never presented periodic 
structures. 
(3) ground and microwave measurements 
were always concurrently collected on 
the same field area, 
(4) sampling strategies of ground 
measurements were adapted to provide 
accurate estimates of the soil 
parameters, 
Very few attempts have been made to 
extend these results in the case of the 
survey of large field area. One of the 
most important reasons is related to 
lack of ground based data necessary to 
obtain accurate calibration 
re 1ationships. 
In the case of sensors operating in one 
single and non optimal configuration , 
it may be questionned if the use of 
physical models, like the physical 
optics model, will be an useful tool to 
retrieve soil moisture from remote 
data. Models have limited conditions of 
validity and it necessary requires a- 
priori knowledges of surface roughness 
parameters whose field determinations 
are generally difficult. 
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