Multi-frequency SAR measurements provide more exhaustive information of a given scattering scenario, compared to the single-frequency case, due to the sensitivity of longer and shorter wavelengths to scatterers of different size. In combination with polarimetry, they potentially allow to retrieve geometric and dielectric properties of scatterers at different size scales. For snow and ice scenarios, this means that it should be possible to study snow and ice microstructure at high frequencies (e.g. X-band) while for larger features, like ice lenses and subsurface layers, lower frequencies (L-band) should be preferred. In addition, the penetration depth of microwaves increases with increasing wavelength, making higher frequencies more sensitive to surface and shallow subsurface layer, and lower frequencies more suitable to sense features located deeper (down to some tens of meters).
Due to the complexity of the scattering scenario, the exploitation of PolSAR data still plays a secondary role in the retrieval of snow and ice properties. Most of the previous works focused on the analysis and modeling of the amplitude (or intensity) of the backscattered signal at different polarizations. Recent studies have shown that also the coherent nature of the polarimetric signature is essential. For instance, it has been shown that polarimetric phase differences between the HH and VV channels can reveal details of the microstructure of snow and firn layers ,.
In this study, a multi-frequency analysis of polarimetric signatures over the different ice zones of the Greenland ice sheet is carried out. The objective is to assess the potential of polarimetric SAR to identify ice zones by means of different scattering mechanisms related to their peculiar surface and subsurface features. A set of descriptors is employed to extract and interpret the polarimetric information from the data, which includes backscattering coefficients, the scattering entropy, the mean alpha angle, polarimetric ratios and phase differences. The study is based on a multi-frequency (L-, C- and X- band) airborne Pol-SAR dataset acquired in May 2015, during the ARCTIC15 campaign, over a 200km long (and 5 km wide) transect in West Greenland.
 Leinss S., Parrella G. and Hajnsek I.: Snow height determination by polarimetric phase differences in X-band SAR data, JSTARS, vol. 7, no. 9, pp. 3794-3810, 2014.
 Parrella G., Hajnsek I. and Papathanassiou K.: On the interpretation of polarimetric phase differences in SAR data over land ice, GRSL, vol. 13, no. 2, pp. 192-196, 2016.