Abstract
Pseudo quad polarimetric (quad-pol) image reconstruction from the hybrid dual-pol (or compact polarimetric (CP)) synthetic aperture radar (SAR) imagery is a category of important techniques for radar polarimetric applications. There are three key aspects concerned in the literature for the reconstruction methods, i.e., the scattering symmetric assumption, the reconstruction model, and the solving approach of the unknowns. Since CP measurements depend on the CP mode configurations, different reconstruction procedures were designed when the transmit wave varies, which means the reconstruction procedures were not unified. In this study, we propose a unified reconstruction framework for the general CP mode, which is applicable to the mode with an arbitrary transmitted ellipse wave. The unified reconstruction procedure is based on the formalized CP descriptors. The general CP symmetric scattering model-based three-component decomposition method is also employed to fit the reconstruction model parameter. Finally, a least squares (LS) estimation method, which was proposed for the linear π/4 CP data, is extended for the arbitrary CP mode to estimate the solution of the system of non-linear equations. Validation is carried out based on polarimetric data sets from both RADARSAT-2 (C-band) and ALOS-2/PALSAR (L-band), to compare the performances of reconstruction models, methods, and CP modes.
Highlights
Synthetic Aperture Radar (SAR) uses electromagnetic waves to characterize target geometrical structures and dielectric properties
The quantitative result is consistent with the explanation for the results shown in Results in Figures 5 and 6b, and Table 3 show that a same method performs differently for different terrain types when the compact polarimetric (CP) mode varies
When the real co-polarized phase difference (CPD) is close to ±π, a small perturbation on the estimated h|SHV |2 i will lead to dramatic changes of ±2π in the estimated CPD, as can be observed in Figure 6a that in the π/4 mode a certain amount of pixels lies in the corners of (−π, π) and (π, −π)
Summary
Synthetic Aperture Radar (SAR) uses electromagnetic waves to characterize target geometrical structures and dielectric properties. For the single-polarization transmit and single-polarization receive case, which corresponds to a single-pol system, target backscatter is characterized by a single scattering coefficient. For the single-polarization transmit and orthogonal-polarization simultaneous receive case, which corresponds to the dual-pol system, backscatter is characterized by a complex scattering vector. If we alternatively transmit orthogonal polarizations and use orthogonal polarizations to simultaneously receive backscatter, we get the scattering matrix, and this corresponds to the full-pol (FP) system. The dual-pol system is discussed in two cases, i.e., the conventional dual-pol imaging mode (HH/HV or VH/VV) and the hybrid dual-pol imaging mode (i.e., the transmitted wave is not H or V polarized, generally known as compact polarimetry). Some studies have shown that the compact polarimetric (CP) mode performs
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