Sea Ice Climate Data from Satellites
Nansen Environmental and Remote Sensing Center g, NORWAY
The European Space Agency has launched the Climate Change Initiative programme, which aims to provide long-term satellite-based data for climate research. CGOS has defined a set essential climate variables (ECV) that can only be quantified on global scale by use of satellite observations, and sea ice is one of these variables. There are more than three decades of passive microwave data for retrieval of sea ice concentration and two decades of radar altimeter data for ice thickness estimation. In order to improve sea ice modelling and validate coupled global climate models, it is necessary to provide homogeneous and quality-controlled data sets on sea ice variables. This work is presently undertaken in the ESA CCI sea ice project with focus on sea ice concentration (SIC) and sea ice thickness (SIT). There are, however, several other sea ice variables of importance for climate research such as ice drift, leads, polynyas, melt ponds, snow thickness, surface temperature and others. Retrieval of quantitative estimates of these variables from satellite data is an ongoing research activity, and long time series of these variables are not yet available. A user requirement analysis has been performed to quantify accuracy, coverage, resolution and stability of the SIC and SIT data sets by different user groups. The requirements addressed model development, model validation, model initialisation, data assimilation, and other climate research activities such as time series analysis. In order to provide the "best algorithms" for retrieval of SIC and SIT data sets, a algorithm intercomparison exercise is conducted, where the retrieval methods are analyzed for different seasons and geographical regions. One specific issue is to determine the error sources in the data processing chain and estimate the total error of the ECV data set. After the ECV data sets are produced usjng the "best algorithm" a validation study will be conducted where independent data sets form other satellite data, airborne surveys and in situ observations are used. The sea ice ECVs will be used by the Climate Modelling User Group, established under the ESA CCI programme to validate climate models using results from all the CCI projects. Sea ice ECVs will be important for validation of climate models in the Arctic and Antarctic, where sea ice is a sensitive climate variable. Sea ice ECVs are also important for many other users groups, such as operational sea ice services, marine transportation, oil and gas exploration, marine ecosystem research, fishery management, and protection of the environment in the polar regions.