3-D Characterization of Snowpacks at X and Ku Bands by VHR Tomography using the GB-PoSAR Multibaseline System.
Laurent, Ferro-Famil1; Tebaldini, Stefano2; Davy, Matthieu1; Boutet, Frederic1
1University of Rennes 1, IETR, FRANCE; 2Politecnico Milano, ITALY

Monitoring snowpack properties is an important issue concerning snow forecasting, prevision of natural hazards like snow avalanches, economic arrangements related to tourism and winter sports, and also a relevant asset in the present context of climate change. Synthetic Aperture Radar (SAR) is an important technology for snowpack characterization in a natural en vironment, as it provides large spatial coverage, resolution on the order of few meters, and the possibility to operate largely independentely on weather conditions and Sun illumination. Moreover, by virtue of the penetration capabilities of Radar waves, SAR data provide sensitivity to the vertical structure of the snowpack, therefore revealing information hidden to optical sensors.
For all these reasons a considerable number of works has appeared in literature addressing the interaction of Radar waves with snow and ice and the exploitation of SAR data for snowpack remote sensing applications. With this paper we aim at characterizing the snowpack by providing a three dimensional (3D) reconstruction of its Radar reflectivity, which is obtained by focusing in the 3D space multiple SAR acquisitions gathered from slightly different points of view. This approach has been largely considered in recent years for forestry applications as it entails a fundamental advantage over traditional (i.e.: 2D) SAR imaging, namely the possibility to see the vertical structure of the imaged volume, to be afterwards employed as a robust basis for validation and development of physical models. The results presented in this paper have been obtained by processing data from Ground Based (GB) Multi-Baseline SAR campaign carried out by the University of Rennes I at Col de Porte, in the French Alps, in collaboration with Meteo-France and in the frame of the ALPSAR project in teh Austrian Alps. The illuminated scene is limited to a
few square meters. Yet spatial resolution is on the order of few centimeters in the three directions, which allowed to image a snowpack to a sufficiently fine resolution so as to reveal its vertical structure. The most remarkable finding is the presence of strong backscattering contributions from beneath the snow layer. Such contributions appear to be linked to the presence of an ice layer, as supported by direct observations and in-situ data.