On the qualification of available sea ice freeboard data for the validation of remote sensing observations
The significant loss of Arctic sea ice during the last decades shows the sensitivity of the sea ice system to changes in the global climate. To distinguish between natural variability and the impact of global warming, an understanding of processes and feedbacks is necessary and for that, consistent and comprehensive measurements of the most important sea ice properties are required. While sea ice concentration is observed routinely year-round since the beginning of the satellite era, strategies to investigate the sea ice thickness distribution, crucially needed for an investigation of ice mass changes, has only recently been developed. To contribute to the interpretation of the remotely sensed sea ice thickness products, which are mainly based on freeboard determination from altimeter measurements, available airborne sea ice thickness and freeboard data have been collected within the Sea Ice Downstream Services for Arctic and Antarctic Users and Stakeholders (SIDARUS) EU-Project, and have been analyzed with respect to their usability for validation of the large scale satellite products. Thus, statistical parameters like the variability of freeboards within the common footprint areas of satellites have been analyzed from measurements made during the PAMARCMIP 2011 campaign to determine the differences between point measurements and areal averages. Also, impacts on the deviated sea ice thicknesses have been studied by means of a cross validation of freeboard-based sea ice thicknesses with airborne thickness measurements with electromagnetic induction sounding. Finally, since during the PAMARCMIP campaign few flights were performed in conjunction with CryoSat-2 overpasses, the airborne-based freeboards can finally be used for a comparison with satellite-derived data.