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Mesures physiques et signatures en télédétection

L.Rakotoarivony, O.Taconet, M.Bcnallegue, D.Vidal-Madjar
CETP/CNRS 10-12 Avenue de l'Europe 78140 Velizy FRANCE
Abstract: The EEM model is an electromagnetic scattering model based on an approximate solution of
the tangential field. New contributions of this model in comparison with all classical models (PO, GO,
SPM) are its large range validity and its ability to take account of complex surface structure by
integrating the two dimensional expression of the correlation function of the surface heights.
Our purpose is to compare simulation result from the IEM model with experimental data base of the radar
backscattering o° measured with an airborne radar over agricultural fields of bare soil with various tillage
practices (ploughings, sowings...).
A considerable effort has been devoted in remote sensing to the study of radar backscattering response of
natural surface because of its potentiality to retrieve parameters of surface (humidity, roughness...).
Our study concerns the radar backscattering over agricultural surface of bare soils. As this problem is
based on electromagnetic wave diffusion, our approach is an electromagnetic model which has the most
largest validity and which is able to integrate a complex surface like agricultural surfaces.
In the first time, a short description of the EEM model will be presented. In second time, a bidimensional
parametrization of agricultural surface heights used for the IEM model will be introduced. It describes
the soil roughness at small scale (clods) and large scale (rows). Before concluding, sensitivity of the IEM
model and comparison between simulation and measurements will be presented.
2. THE EEM MODEL: Integral Equation Model (Fung 1992)
The IEM model [1] [2] [3] is a backscattering model for scattering from a randomly dielectric rough
surface. This model is based on an approximation solution of a pair of integral equations for the
tangential field. Other electromagnetic backscattering model was developed previously (SPM,PO,GO...)
but their applications are limited. The IEM model brings a new view in backscattering simulation
because of its large validity range and its potentiality to integrate complex surfaces.
In term of ks and kl (k the wave number, s the height RMS and 1 the correlation length of the surface),
the validity range of the IEM model is presented in the figure 1, in comparison with those of classical
k : Wave number
s : Height RMS
1 : Correlation lenght
SPM : Small Perturbation Model
GO : Geometrical Optic Model
PO : Physical Optic Model
IEM Range Validity
figure l
h C-HH