Science Service System

Summary of Proposal MTH0123

TitleDry snow zone and accumulation mapping on polar ice sheets
Investigator Dierking, Wolfgang - Alfred Wegener Institute for Polar and Marine Research, Climate Sciences
Team Members
Dr. Dierking, Wolfgang - Alfred Wegener Institute for Polar and Marine Research, Climate Science
Dr. Rack, Wolfgang - Gateway Antarctica, Centre for Antarctic Studies and Research
Prof. Dr. Rott, Helmut - University of Innsbruck, Institute for Meteorology and Geophysics
SummaryOur proposal aims to measure the extent of the dry snow zone and its snow accumulation, as well as the temporal and spatial variability thereof. This is of relevance for the validation of present climate models, which predict significant environmental changes in polar areas, as well as for the generation of input data for numerical ice sheet models. On ice sheets, the dry snow line, which separates the percolation zone from the dry snow zone, reacts sensitively to the rising maximum summer temperatures, because a small lift of the 0C limit triggers in comparable flat terrain a large horizontal shift of the dry snow line towards the inland. We propose a combination of X- and C-Band SAR images for the ice sheet of Greenland and for key regions of the Antarctic ice sheet. SAR images will be acquired during winter, because the information of extreme melting events is preserved in the snowpack as refrozen ice lenses, which act as strong scatterers. We expect that the calibrated and normalized backscattered power is similar for both frequencies in the percolation zone, but shows significant differences in the homogenous snow pack of the dry snow zone. Such a backscattering behaviour was observed with spaceborne scatterometers for C- in combination with Ku-Band, and has to be demonstrated in combination with X-Band. The feasibility of the method will be demonstrated at a test site in Greenland (EGIG line) and Antarctica (Dronning Maud Land), where ground truth is already available and will be complemented during the course of the project. Ground truth data will also be made available by GA in the western Ross Sea region from field work within the Cryosat-2 validation activities starting in 2008/09. Building up on existing numerical models, we will study the sensitivity and robustness of our method. Data are to be acquired in full resolution and ScanSAR mode over the winter periods of several months, when the backscattering of the snowpack is stable. We expect that the sensitivity to detect the dry snow line depends on the frequency and strength of melting cycles, as well as on the slope of the terrain. The results of the signature study will be used to investigate the potential of X-band to map snow accumulation in the dry snow zone. TerraSAR-X offers for the first time the possibility to map the dry snow line of ice sheets at high spatial resolution. The International Polar Year 2007/08 (IPY) just falls within the acquisition period of TerraSAR-X, and overlaps with ESAs Cryosat mission. Internationally coordinated activities for ground truth measurements with the participation of AWI and GA are planned within the frame of IPY and the Cryosat Calibration and Validation activities. This offers the unique possibility of almost simultaneous ground truth measurements, which will serve to proof the method and as indispensable input to modelling studies. The outcome of this study will be assessments on the usefulness of TerraSAR-X for detecting the dry snow line and for estimating snow accumulation rates. Algorithms needed for these tasks will be improved/developed. Results will be reported on international conferences and in refereed international journals. For the accumulation study, funding was provided for a Ph.D. student by the German Science Foundation. Wolfgang Dierking will also directly contribute to this study. He is on a permanent position at the AWI. Wolfgang Rack will work on backscattering signature analysis of snow with low and high resolution satellite data and will provide in situ data from the Ross Sea Region. His emphasis is the investigation of the dry snow line. Wolfgang Rack is on a permanent position at GA and holds a guest contract at AWI.

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