Validation of ice edges derived from SSM/I data using ERS-SAR images

For the monitoring of sea ice commonly the 19 and 37 GHz channels of the SSM/I (Special Sensor Microwave/Imager) are used. The low spatial resolution of these channels in the order of 50/spl times/50 km/sup 2/ affects the spatial accuracy of the ice edge defined by the 15% ice concentration isoline. For the determination of a higher resolved ice edge, an ice edge detection algorithm (IED) was developed using the information of the 85 GHz channels with a resolution in the order of 15/spl times/15 km/sup 2/. The influence of weather effects on the 85 GHz signal is reduced by combining it with information of the 37 GHz channels. The Validation of IED ice edge locations using ERS-1/2 synthetic aperture radar (SAR) images shows that the accuracy is better than 10 km. Two typical situations are considered in detail. If the MIZ consists of a diffuse sea ice distribution with a weak ice concentration gradient, the IED detects the ice edge between the 45% and 75% isolines depending on ice conditions. If the MIZ consists of a compact ice field sharply separated from open water, the IED is able to detect the ice edge correctly but its location is close to the 30% isoline. In both cases the IED provides a reliable estimate of the borderline of compact sea ice which can serve as a definition of the ice edge.