A STUDY OF BACKSCATTERING FROM MULTISCALE ROUGH-SURFACE

Most of the rough surfaces are generally multiscale in nature as obser ved by radar even at narrow-band. In this paper, we apply the modulati on concept to study the characteristics of backscattering from such a multiscale surface, using the IEM scattering model. The modulated surf ace is special kind of multiscale surface in that a random surface is superimposed upon a periodic type surface. The modulation is rationed from the fact the measured correlation function usually exhibits zero- crossing which equally states the fact that the maxima of surface spec tra is shifted toward the higher wavenumber. The amount of the frequen cy shift depends on the modulation wavenumber. It changes the spectral decay rates behind the peak valued. The normal incidence angle can be significantly shifted as well. It is also found the maximum modulatio n wavenumber is related by the inverse of base-band correlation length . In all cases studied, it was found that the modulation effects signi ficantly changes the backscattering behavior, both its angular trend a nd level, and is polarization dependent. It is inferred from this stud y that the actual surface correlation length is very difficult to meas ure and may not be defined by a single parameter. In fact, radar can o nly observe effective correlation length under an operation frequency, which in turns depends on modulation wavenumber. In particular, in te rms of retrieval, the correlation length measured by the radar and tha t by field measured may have quite different meanings.