Abstract
Polarimetric Synthetic Aperture Radar (PolSAR) images containing cities may exhibit misclassified areas when using polarimetric decompositions. Several articles relate this problem to the effects of orientation between the facades of buildings and the acquisition trajectory. Materials also play a role in polarimetric behavior. This paper deals with this combined effect of material and orientation. It analyzes different sets of data, airborne or space-borne, at L-, C- and X-bands, and for different orientation angles. It shows that considering dielectric dihedral rather than metallic in the polarimetric mechanism of double-bounce has a very important impact on the differences of intensities between the channels HH and VV. This difference is very important for small angles of orientation, and then decreases for large angles. Furthermore, the curves of the ratios between polarimetric intensities as a function of the orientation angle vary little with the materials and the frequencies encountered in all the scenarios envisaged. The signal of the ratio VV/HH raises a plateau around −1 dB for orientations higher than 30°. We also observe a plateau for HV/HH, but with a value around −5 dB.
Highlights
In Synthetic Aperture Radar (SAR) images, urban areas are often characterized by many high responses resulting from scattering by dihedral structures
When Freeman and Durden introduced the so-called Freeman–Durden Decomposition [1], their goal was to interpret radar backscattering from forests
When Yamaguchi and his co-authors introduced the fourth-component scattering model [2], their goal was to apply the tool of Freeman and Durden to SAR images containing urban areas
Summary
In Synthetic Aperture Radar (SAR) images, urban areas are often characterized by many high responses resulting from scattering by dihedral structures. This observation has been exploited in model-based decompositions to help for the classification. The classical color code is applied: red refers to double-bounces, blue to single scattering, and green to cross-polarization contribution For this basis, the double-bounce is an ideal scattering mechanism modeled by a perfectly aligned dihedral corner reflector made of Perfectly Electrically Conducting (PEC) material. The double-bounce is an ideal scattering mechanism modeled by a perfectly aligned dihedral corner reflector made of Perfectly Electrically Conducting (PEC) material With this pure double-bounce, VV and HH intensities are equal, and there is no cross-polarization
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