| Summary: | Polarimetric and (multi-baseline) interferometric SAR techniques are promising tools to investigate the subsurface properties of glaciers and ice sheets, due to the signal penetration of up to several tens of meters into dry snow, firn, and ice. Two different lines of research were addressed in recent years. The first is based on PolSAR, which provides not only information about the scattering mechanisms, but also has the uniqueness of being sensitive to anisotropic signal propagation in non-scattering layers of snow and firn. The second line of research is related to the use of Pol-InSAR and TomoSAR to retrieve the 3D location of scatterers within the subsurface. So far, the different SAR techniques were mainly assessed separately. In the field of PolSAR modeling efforts have been dedicated to establish a link between the co-polarization HH-VV phase difference (CPD) and the structural properties of firn [1]. CPDs have then been interpreted as the result of propagation effects due to the dielectric anisotropy of the firn volume. This modeling approach establishes a relationship between the measured CPD and firn density, firn anisotropy and the vertical backscattering distribution in the subsurface of the glacier or ice sheet. By assuming bulk values for density and anisotropy and employing a constant signal extinction for the vertical backscattering function, i.e. a uniform volume, a first attempt to retrieve firn thickness from PolSAR data was presented [1]. In the fields of Pol-InSAR and TomoSAR for the investigation of the subsurface scattering structure of glaciers and ice sheets, recent studies were concerned with the estimation of the vertical backscatter distribution, either model-based or through tomographic imaging techniques. The complexity of (Pol-)InSAR models for the retrieval of subsurface structure information is mainly limited by the available observation space. Thus, constant signal extinction volumes [2], with additional Dirac deltas to represent refrozen melt layers [3] and variable extinction ...
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