[1] A statistical analysis was performed for nearly simultaneously acquired C band synthetic aperture radar (SAR) images and ice freeboard statistics. The data analyzed were collected during a CryoSat calibration-validation campaign in March 2005 in the Baltic Sea. The 3-D ice freeboard topography along transects with a total length about 150 km and width of 300 m was constructed from cross-track scanning airborne laser scanner measurements. The SAR image data set consisted of two nearly coincident Envisat Advanced Synthetic Aperture Radar alternating polarization precision and image mode precision images at HH polarization with their incidence angle ranges deviating about 20°. The data set represents primarily low-salinity thin first year ice with high ice concentration and thin snow cover under cold weather conditions. The variance of the mean freeboard increased with increasing mean freeboard with the chosen window size (300 m) up to the mean freeboard of 15 cm. This multiplicative character of sea ice cover forms the basis by which we can expect that the C band backscattering coefficient response, which depends only on the ice surface roughness and the top part of ice medium, can provide information on the sea ice thickness. A nonlinear regression model with three control variables, the backscattering coefficient, the dominant thickness of the level ice which has deformed, and a variable accounting the effect of the SAR incidence angle, was established to predict the variation of the ice freeboard. The applied Bayesian approach also provided means to estimate the uncertainty range for the model fitting and the model predictions. The modeled predictions were mostly in good agreement with the measured values. The predictions for three different test lines accounted for 67%-85% of the measured freeboard variance in 300 m scale. In cold conditions with thin snow cover it was possible to estimate the degree of ice deformation and ice thickness quantitatively from C band SAR images.Citation: Similä, M., M. Mäkynen, and I. Heiler (2010), Comparison between C band synthetic aperture radar and 3-D laser scanner statistics for the
Melt pond coverage of sea ice in the High Arctic was observed for a period of 28 days: from 24 June to 21 July 2007. Pond fractions were computed from digital photographs automatically obtained with a camera and computer unit mounted in the mast of the drifting polar schooner Tara. The area visible in the series of images corresponds to approximately 6400 m 2 on the ice. By applying iterative image classification methods, the images were partitioned into melt ponds and other surface types, such as ice or snow. The percentage of melt ponds could be calculated for 22 out of 28 days. Six days were omitted from the analysis because of weather conditions causing poor visibility. Melt pond coverage was seen to rise rapidly shortly after the melt ponds started forming: between 24 and 30 June 2007 the pond fraction increased from 3 to 14%. After the first rapid growth period, the pond fraction increased more gradually, reaching 15% at the end of the data collection period (21 July 2007). Estimated with additional data, the maximum melt pond coverage was reached in mid-August, and totalled 32-42%. Melt onset date and the initial rapid melt pond growth agree well with previous research, but the areal pond coverage appears surprisingly high for the latitude (88°N). Direct comparison with previously observed melt pond coverage is rendered difficult by scarce observations of pond coverage sufficiently high up in the Arctic.
Melt pond coverage of sea ice in the High Arctic was observed for a period of 28 days: from 24 June to 21 July 2007. Pond fractions were computed from digital photographs automatically obtained with a camera and computer unit mounted in the mast of the drifting polar schooner Tara. The area visible in the series of images corresponds to approximately 6400 m 2 on the ice. By applying iterative image classification methods, the images were partitioned into melt ponds and other surface types, such as ice or snow. The percentage of melt ponds could be calculated for 22 out of 28 days. Six days were omitted from the analysis because of weather conditions causing poor visibility. Melt pond coverage was seen to rise rapidly shortly after the melt ponds started forming: between 24 and 30 June 2007 the pond fraction increased from 3 to 14%. After the first rapid growth period, the pond fraction increased more gradually, reaching 15% at the end of the data collection period (21 July 2007). Estimated with additional data, the maximum melt pond coverage was reached in mid-August, and totalled 32-42%. Melt onset date and the initial rapid melt pond growth agree well with previous research, but the areal pond coverage appears surprisingly high for the latitude (88°N). Direct comparison with previously observed melt pond coverage is rendered difficult by scarce observations of pond coverage sufficiently high up in the Arctic.
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