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A laser profiler mounted on a helicopter was used to measure the surface topography of sea ice in the Weddell Sea. The measurements were carried out during the cruise Antarktis X/4 of R/V Polarstern as part of the Winter Weddell Gyre Study 1992 (WWGS′92). The total length of the measured surface profiles amounts to 793 km. The observed mean ridge heights and mean ridge spacings are fairly well correlated. Therefore the ridging intensity R1, which is the ratio of ridge height and spacing, was used as a quantitative classifier in order to arrange the laser data into different groups. At a cutoff height of 0.8 m the average ridge height and spacing are 1.16 m and 160 m at the lowermost range of ridging intensities (R1<0.02), 1.2 m and 50 m at the intermediate range (0.020.04), respectively. The best fits to the observed ridge height distributions are achieved by negative exponentials, at lower ridging intensities as a function of ridge height, at the regime of highest ridging intensity as a function of the ridge height squared. The distributions of ridge spacing are well described by a lognormal distribution function. A simple model is used to estimate the average thickness hd* and the areal fraction of ridged ice from the laser data. The values of hd* range from 3.1m with an areal coverage of 5% at the lowermost range of R1 to 3.7 m with an areal coverage of 31% at the uppermost range. If the ridged ice is distributed as a uniform layer over a unit area, the corresponding effective thickness values are 0.14 m and 1.16 m, respectively. Mean ridge heights and spacings are determined for different cutoff heights in order to enable comparisons to other measurements. The effect of ridges on the surface stress over the ice is estimated using the drag partition theory, which is applicable to the regime of lowest ridging intensity. The contribution of ice ridge form drag to the total wind drag for an average ridging intensity of = 0.007 and a cutoff height of 0.8 m is about 35 to 40% at neutral stability. If it is assumed that the aerodynamic roughness length z0 of the intervening ice surface varies between 3.3×10−4 m and 5.5×10−4 m, the drag coefficient Cdn ranges from 2.08×10−3 to 2.24×10−3 at a reference height of 10 m.

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Abstract. Quantitative parameters characterizing the sea ice surface topography are needed in geophysical investigations such as studies on atmosphere-ice interactions or sea ice mechanics. Recently, the use of space-borne single-pass interferometric synthetic aperture radar (InSAR) for retrieving the ice surface topography has attracted notice among geophysicists. In this paper the potential of InSAR measurements is examined for several satellite configurations and radar frequencies, considering statistics of heights and widths of ice ridges as well as possible magnitudes of ice drift. It is shown that, theoretically, surface height variations can be retrieved with relative errors ≤ 0.5 m. In practice, however, the sea ice drift and open water leads may contribute significantly to the measured interferometric phase. Another essential factor is the dependence of the achievable interferometric baseline on the satellite orbit configurations. Possibilities to assess the influence of different factors on the measurement accuracy are demonstrated: signal-to-noise ratio, presence of a snow layer, and the penetration depth into the ice. Practical examples of sea surface height retrievals from bistatic SAR images collected during the TanDEM-X Science Phase are presented.