Classification of Baltic Sea ice types by airborne multifrequency microwave radiometer

An airborne multifrequency radiometer (24, 34, 48, and 94 GHz, vertical polarization) was used to investigate the behavior of the brightness temperature of different sea ice types in the Gulf of Bothnia (Baltic Sea). The measurements and the main results of the analysis are presented. The measurements were made in dry and wet conditions (air temperature above and below 0/spl deg/C). The angle of incidence was 45/spl deg/ in all measurements. The following topics are evaluated: a) frequency dependency of the brightness temperature of different ice types, b) the capability of the multifrequency radiometer to classify ice types for winter navigation purposes, and c) the optimum measurement frequencies for mapping sea ice. The weather conditions had a significant impact on the radiometric signatures of some ice types (snow-covered compact pack ice and frost-covered new ice); the impact was the highest at 94 GHz. In all cases the overall classification accuracy was around 90% (the kappa coefficient was from 0.86 to 0.96) when the optimum channel combination (24/34 GHz and 94 GHz) was used.