Comparison of ERS-SAR Backscattering Coefficients with In Situ Measurements of the Geometrical Structure of the Sea-Ice Surface in Antarctica

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C. Haas, Q. Liu, T. Martin and E. Augstein	*	Alfred-Wegener-Institute for Polar and Marine Research, P.O. Box 12 01 61, D-27515 Bremerhaven, Germany tmartin@awi-bremerhaven.de http://www.awi-bremerhaven.de
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Abstract

The surface morphology of sea ice results from the deformation due to atmospheric and oceanic sea ice forcing. The geometrical structure of the ice covered surface determines the hydrodynamic roughness (form drag) of the air-sea interface and thus influences the interactions between atmosphere, ice and ocean. The deformation of sea ice presents also an archive of the history of its development. Present numerical sea ice models predict among others the ice drift and some characteristics of deformation, which may be related to the ice roughness. For this purpose certain transfer functions may be derived with the aid of satellite remote sensing techniques, which provide information on the geometrical conditions of the sea ice. Within the frame work of the German research programme 'Remote sensing of sea-ice properties and processes' geometric sea-ice surface characteristics are determined from ERS SAR and radar altimeter measurements. Ground-truth data for intercomparison are obtained from helicopter laser altimeter profiling and from thickness measurements with an electromagnetic device as well as from drill holes. The SAR backscatter coefficients are correlated with these data, acquired in the Bellingshausen and Amundsen Seas in February 1994 during an expedition of RV Polarstern. In a first step two significantly different sea-ice regimes are identified: The ice in the central Bellingshausen Sea was moderately deformed with mean thicknesses of 1 to 1.2 m, while the mean ice thickness in the Amundsen Sea ranged from 2 to 3 m. The average ridge height and the average spacing between ridges (cut-off height 0.8 m) were found to be 1.06 m and 207 m in the Bellingshausen Sea and 1.17 m and 47 m in the Amundsen Sea, respect