Space Missions for the Retrieval of Accumulation Rates in Polar Regions

Wolfgang.Dierking [ at ]


Recently the actual contribution of the ice sheets to sea level rise, and the interaction of ice sheets with the surrounding seas, has become an important issue in polar research. To determine the effects of the net mass flux from Greenland and Antarctica to the surrounding ocean, accurate data on mass gain (caused by accumulation of snow over the ice sheets and ice shelves) and mass loss (due to melting and iceberg calving) are required. The main factor of uncertainty arises from the difficulty to correctly determine snow accumulation over large areas. Work from various authors demonstrates a potential for mapping snow accumulation based on data from microwave radiometers, scatterometers, altimeters, and SAR systems (including INSAR and polarimetric SAR). These instruments cover a frequency range from about 1 to 40 GHz. Radar altimeters such as ASIRAS/Cryosat seem to be useful to map the upper annual layer(s) in the percolation and dry snow zone, provided the layers are thick enough (and accumulation rates correspondingly high) to be resolved in the measured radar signals. For the dry snow zone, empirical relationships were presented that relate brightness temperatures or radar intensities to accumulation rates. Another approach is to combine a model of firn structure with a scattering model for accumulation rate retrieval. Here, various problems exist, ranging from a realistic representation of the firn structure to an adequate simulation of the interactions between microwaves and the medium firn. The signal sensitivity to varying accumulation rates is only sufficient at low values of accumulation, and the results are integrals over a depth determined by the microwave frequency and environmental conditions. Field data for validation are sparse and often limited to small depths only. The main conclusion for ice sheets from the work presented so far is that no single sensor and retrieval approach can be regarded optimal for the retrieval of accumulation rates. The need to gather information on accumulation rates over the ice sheets is an excellent example for the need to combine different sensors, field measurements and modelling approaches, hence to interpret the term “mission concept” in a broad sense. In our presentation, we will sketch different approaches for accumulation rate retrieval and try to assess which combinations are most promising, including recently presented ideas for new satellite missions.

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Dierking, W. , Linow, S. and Rack, W. (2014): Space Missions for the Retrieval of Accumulation Rates in Polar Regions , Workshop on Novel Mission Concepts for Snow and Cryosphere Research .

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