SAR OBSERVATIONS OF ARCTIC FREEZE-UP COMPARED TO SSM I DURING ARCTIC-91/

Ice concentration in the Arctic derived from ERS-1 Synthetic Aperture Radar (SAR) and Special Scanning Microwave/Imager (SSM/I) images are c ompared. The satellite data are compared to video images and in situ m easurements. The data were acquired during the freeze-up period of the ARCTIC'91 expedition. The studied areas were characterized by melting conditions and new ice formation with frost flowers. The ERS-1 SAR im ages are classified by a local averaging method and a segmentation met hod. Parameters for the methods are derived from the backscattering di stributions. Temporal sequences and meteorological information are use d for consistent results. Ice concentration derived from SAR are compa red with the SSM/I ice concentration (NASA team algorithm) and ship ob servations. SSM/I may underestimate the ice concentration by 20 per ce nt due to thin ice formation and melting conditions while SAR may over estimate. However, by using the SAR estimate of the different ice clas ses we believe it is possible to increase the accuracy of the NASA tea m algorithm. We conclude that it is important to compare results from different sensors and methods.