X- and Ku-band Snow Backscatter Signatures from the SARALPS-2007 Campaign

Over a 70-day period from January 2007, a ground-based SAR imaging campaign was carried out in the Austrian Alps with the University of Cranfield’s portable Ground-Based Synthetic Aperture Radar (GB-SAR) system, in collaboration with ENVEO of Innsbruck. The campaign was in support of the proposed COld REgions Hydrology High-resolution Observatory (CoReH2O) satellite mission, selected for assessment by the European Space Agency within the Earth Explorer Programme. The mission will use a dual-frequency SAR, operating at centre frequencies of 10 and 17 GHz, with co- and cross polarizations. The mission is aimed at filling current gaps in spatially detailed information on snow and ice for climate research, hydrology and glaciology. It is proposed that the dual-frequency combination offers the best diagnostic with which to determine critical snow and ice parameters (metamorphic state, depth, SWE). The GB-SAR system is a fully polarimetric, stepped-frequency CW system which uses large bandwidths to provide imagery at resolutions down to a few wavelengths. Polarimetric backscatter signatures of snow at 10 GHz and 17 GHz were acquired together over an incidence angle range of 20°-70°, supported by detailed snow field measurements. Data was collected on seven different dates between mid-January and the end of March 2007, at two sites at 1800 m and 1100 m elevation, respectively. In addition to the Sigma 0 measurement of undisturbed snow, experiments were performed on the effects of snow compaction, surface roughening, as well as the digging of pits in the scene to allow measurement of the uncovered ground and determination of the background signature. Occasional InSAR and PolInSAR measurements were also made during the campaign. The GB-SAR measurements have provided a unique database on the dual-frequency behaviour of snow, over a wide range of different snow conditions, including dry snow with different metamorphic conditions, melting snow, and completely wet snow. One extended day campaign provided a time-series of the backscatter behaviour associated with the development of a re-freezing crust on top of a wet snow pack. The observed frequency behaviour and polarimetric properties of snow backscatter have been extensively compared to theoretical backscatter models for validation and support of the preparation of the snow retrieval algorithms for the CoReH20 mission. This presentation will primarily focus on the experimental methodology, data analysis and derived results.