C- and L-band SAR signatures of Arctic sea ice during freeze-up

Identifying sea ice types in the early stages of development from L-band SAR imagery remains an active research area during the Arctic freeze-up period. We used ScanSAR C- and L-band imagery from RADARSAT-2, ALOS PALSAR and ALOS-2 PALSAR-2, to identify ice types in the North Water Polynya (NOW) and Victoria Strait (VS) region of the Canadian Arctic. We investigated the HH-polarized microwave backscatter coefficient (sigma(0)(HH)) and its GLCM texture parameters for six ice classes and open water. We found very low sigma(0)(HH) for nilas at both C- and L-band. Although similar sigma(0)(HH) found for grey ice at both frequencies, sigma(0)(HH) decrease with increasing ice thickness at L-band from grey ice, whereas, at C-band, sigma(0)(HH) increases from grey to grey-white ice and then decreases as the ice grows. GLCM texture parameters show lower values for L-band than C-band; however, separability among classes was found only for a few selected parameters. We used the support vector machine (SVM) algorithm for ice type classification from SAR scenes using sigma(0)(HH) and GLCM texture statistics. Due to overlapping sigma(0)(HH) signatures at C-band, early-stage ice classes were substantially misclassified. L-band identified early-stage ice classes with higher accuracy compared to C-band but misclassified thicker ice types and open water. L-band alone provided very good classification results (similar to 80% accuracy) and combining L- and C-band (i.e., dual-frequency approach) further increased accuracy to >90%. C-band alone resulted in the lowest accuracy of <60%. We acknowledge that developing a universal ice classification is still a challenge and requires some manual supervision to adopt variable ice conditions into the classification method. However, a dual-frequency approach can achieve higher classification accuracy than conventionally used single-frequency approaches. This research highlights the value of upcoming L-Band SAR missions to improve sea ice classification in regions where a variety of ice types exist, including many thinner types, which are now dominating an increasingly warming Arctic.

Automated summary

This study used C-band and L-band SAR imagery to identify ice types in the Canadian Arctic and compared their features and classification accuracy. It was found that the dual-frequency approach improved classification accuracy, and the classification results of L-band alone were good.