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Estimating the equilibrium line of Devon Ice Cap, Nunavut, from RADARSAT-1 ScanSAR wide imagery

C-band synthetic aperture radar (SAR) imagery from RADARSAT-1 is used to estimate the equilibrium line of Devon Ice Cap, Nunavut, over 3 years (2004–2006). The equilibrium line is determined from the interpretation of radar glacier zones and the transient snow line (TSL). Winter SAR data cannot be used to accurately estimate the equilibrium line because the firn line obscures the end-of-summer TSL, and accumulated superimposed ice cannot be identified. A methodology to estimate the equilibrium line from frequent summer SAR acquisitions is proposed. The TSL is tracked through the ablation season, and the equilibrium line is estimated as being equal to its maximum elevation. The summer SAR data are compared with near-surface air temperatures, QuikSCAT backscatter, optical imagery, and in situ mass balance measurements. The summer SAR-derived equilibrium line altitude (ELA) is always estimated as being above the in situ measured ELA because accumulated superimposed ice cannot be identified. Uncertainty in the equilibrium line estimation is reduced where slopes face the radar look direction. The summer SAR data provide a more accurate estimation of the equilibrium line than winter data, and the estimated equilibrium line can be used to infer relative changes in net balance between years.