| Popis: |
The significant loss of Arctic sea ice during the last decades shows the sensitivity of the sea-ice system to changes in 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 have been developed only recently. These are crucially required for an examination of sea-ice mass changes. Presently, ice thickness observations are mainly based on freeboard measurements by means of satellite laser and radar altimetry. To contribute to the interpretation of these sea-ice thickness products, available airborne thickness and freeboard data were 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 the validation of the large-scale satellite products. One major challenge in comparing satellite and airborne measurements is the different footprint area of these methods. Therefore, statistical parameters like the variability of freeboard within the common footprint areas have been analyzed from measurements made during the PAMARCMIP 2011 campaign in order to determine the differences between point measurements and areal averages. It turned out that mean freeboard is less dependent of the freeboard areas than the modal values are. Furthermore, differences in modal and mean values for the range of chosen footprint areas have been related to their dependency on different ice characteristics and length scales of freeboard and thickness profiles. Also for this comparison, mean values are found to be more representative, as the results are mostly independent from the footprint but depend more on the length scales. However, there was no length scale that was representative for all the observed regions. Finally, results will be used for the interpretation of the comparison between freeboard and sea-ice thickness data derived from different data sources using laser and radar altimetry. |
