TUTORIAL ON SAR POLARIMETRY

2. ROUGH SURFACE SCATTERING MODELS Natural surfaces can be considered as rough, and the roughness is the dominant factor for the scattering behaviour of an EM wave. The roughness of any scattering surfaces is not an intrinsic property of that surface but depends on the properties of a wave being transmitted. Both, the frequency and the local angle of incidence of the transmitted wave, determine how rough or smooth any surface appears to be. The relation of the EM wave in terms of its wavelength λ to the statistical roughness parameter s is given by ks. Thus with increasing wavelength, the roughness term is decreasing, consequently, the indication of relative roughness for any surfaces is depending on the wavelength as k = 2π / λ. Also the local incidence angle plays an important role for defining the roughness condition of a surface. In the near field of the propagating EM wave, the surface appears rougher than in the far field, which can be compared with the reflection of the sunset over the sea. (BECKMANN & SPIZZICHINO 1963). soil matrix Figure 1 Fresnell reflection scheme In case of an ideal smooth surface the characteristics of the reflection can be described by the well known Fresnel Reflectivity Γ. The Fresnel Reflectivity, named after the French Engineer and Physicist Augustin Jean Fresnel (1788-1827), characterises the reflection of a transmitted wave at the interface between two dielectric media n, for example the air n and a 1 ...