Classification of ice properties in the Arctic during freeze-up using ERS-1 SAR and SSM/I

We have studied the ice concentration derived from ERS-1 SAR and SSM/I during the freezeup period of the Arctic-91 expedition. During this complex period we have examples of melting conditions and new ice formation with frost flowers. The ice concentration from the SAR was derived by an averaging method and a segmentation method, and was compared with the SSM/I ice concentration (NASA team algorithm) and ship observations. It was found that the SSM/I values may underestimate the ice concentration by up to 25% compared with the (local) ship observations. ERS-1 SAR images may overestimate the ice concentration. The SAR classification results were also compared with helicopter video observations and it was found that the segmentation method differs up to 10% in the classification results after a period of frost flower formation. Reasons for these discrepancies are discussed. It is concluded that it is important to compare results from different sensors and different methods in combination with temporal sequences and meteorological information and to use only the consistent results.