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Abstract: The high data throughput of spaceborne Synthetic Aperture Radar (SAR) instruments introduces stringent requirements on the end-to-end system, from the on-board storage capacity and data downlink to processing power and archiving capacity in the ground segment. An efficient raw data compression scheme on-board the satellite is therefore required to maximise the return on investment for SAR missions. The next generation of European SAR satellites, the Sentinel-1 mission, will employ the Flexible Dynamic Block Adaptive Quantization (FDBAQ) compression scheme. In order to validate the implementation of the FDBAQ, expected radar reflectivity levels for the global land surface were needed. The paper presents the development of the Global Backscatter Model (GBM) which has been used to simulate realistic radar reflectivity acquisitions in support of performance validation of the Sentinel-1 FDBAQ implementation. The GBM consists of a parameter database and SAR image simulation software. The model parameter database characterises C-band radar reflectivity as a function of local incidence angle with a resolution of 1km for 85% of the global land surface. The parameter database was derived from a global multi-temporal coverage of ENVISAT Advanced Synthetic Aperture Radar (ASAR) data. The SAR image simulation software uses the parameter database together with orbit propagation and swath determination algorithms in order to account for the instrument acquisition geometry and the location specific backscattering characteristics. The model has the potential to simulate acquisitions for other SAR instruments. Furthermore, the parameter database could be a valuable source of information for global land cover studies. [Copyright &y& Elsevier]

The variability of snowmelt dates is important for the terrestrial carbon balance in boreal and subarctic environments. Scatterometers such as the Ku-Band QuikScat have been proven applicable for the detection of surface thaw. We present an improved method for the capture of thaw events based on significance of diurnal differences with respect to long term noise. For each 10 km×10 km grid point two products are derived for the major thaw period: 1) the onset of thaw and 2) the end of daily freeze/thaw cycles at the surface. Both dates may be related to biogeochemical processes, especially carbon fluxes in boreal forests. The onset of the spring thaw period coincides with the first days of increased CO2 fluxes above the late winter baseline. The end of daily freeze/thaw cycles corresponds to the switch from source to sink in evergreen boreal forest environments as illustrated by comparison with eddy-flux tower data and xylem sap flow records from other investigators. The approach is suitable for detecting freeze/thaw cycle periods in boreal forest and tundra biomes. The mean absolute difference in end of freeze/thaw cycling date within the central Siberian study area (3 Mio km2 comprising tundra, boreal forest and steppe grassland) was 9 days for 2000 to 2004. Largest mean differences occurred in the southern taiga and all tundra regions, which were highest for spring 2000. The improved extraction method delivers more precise products from the viewpoint of carbon accounting in evergreen boreal forest environments. This widens the application potential of scatterometer data beyond the current status. [Copyright &y& Elsevier]