| Summary: | Information about ice sheet subsurface properties is crucial for understanding and reducing related uncertainties in mass balance estimations. Key parameters like the firn density, stratigraphy, and the amount of refrozen melt water are conventionally derived from in situ measurements or airborne radar sounders. Both types of measurements provide a great amount of detail, but are very limited in their spatial and temporal coverage and resolution. Synthetic Aperture Radars (SAR) can overcome these limitations due to their capability to provide day-and-night, all-weather acquisitions with resolutions on the order of meters and swath widths of hundreds of kilometers. Long-wavelength SAR systems (e.g. at L- and P-band) 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. Understanding the relationship between geophysical subsurface properties and the backscattered signals measured by a SAR is ongoing research. Two different lines of research were addressed in recent years. The first is based on Polarimetric SAR (PolSAR), which provides not only information about the scattering mechanisms, but also has the uniqueness of being sensitive to anisotropic signal propagation in snow and firn. The second is related to the use of interferometric SAR (InSAR) to retrieve the 3D location of scatterers within the subsurface. Particularly multi-baseline InSAR allows for tomographic imaging (TomoSAR) of the 3D subsurface scattering structure. So far, the potential of the different SAR techniques was only assessed separately. In the field of PolSAR, modeling efforts have been dedicated to establish a link between co-polarization (HH-VV) phase differences (CPDs) and the structural properties of firn [1]. CPDs have then been interpreted as the result of birefringence due to the dielectric anisotropy of firn originating from temperature gradient metamorphism. Moreover, the relation between the anisotropic ...
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