SSM/I sea ice remote sensing for mesoscale ocean-atmosphere interaction analysis

Two algorithms have been used in a hybrid scheme in order to obtain sea ice concentration maps at 12 km resolution from Special Sensor Microwave Imager (SSM/I) data. One algorithm is based on the 85 GHz polarization difference. The second algorithm is the NASA Team algorithm using the 19 and 37 GHz SSM/I channels. Using 85 GHz SSM/I data allows a significant resolution improvement compared to 19 GHz SSM/I data. This. however, requires careful consideration of the larger atmospheric opacity affecting SSM/I measurements at 85 GHz (weather influence) which can lead to incorrect sea ice concentration estimates particularly over open water. Our scheme combines the high spatial resolution achieved with the 85 GHz channels with the almost weather-independently NTA-based decision whether the data points belong to the ice-free ocean or to the ice-covered area. Reference 85 GHz brightness temperatures (tie points) have been estimated using a statistical linear regression method with the aid of independent sea ice concentration reference data. These were derived from aircraft dual-polarized passive microwave measurements at 19 and 37 GHz and optical line scanner images. The evaluation of 30 days of SSM/I data comparing the NTA and 85 GHz ice concentrations indicates a good agreement and a strong linear relationship. ERS-2 SAR and SSM/I data were used to analyze the evolution of the Storfjorden Polynya and the MIZ in the Fram Strait. Two different numerical atmospheric models were used to analyze the effect of a resolution improvement from 50 to 12 km of the sea ice concentration data prescribed to model the atmospheric boundary layer (ABL). It was found that the representation of the MIZ substantially influences the modelled ABL temperatures. Temperature profiles obtained with the model using the high resolution sea ice concentration data agree significantly better with the profiles measured by the aircraft.