On the estimation of spring melt in the North Water Polynya using RADARSAT-1

This paper evaluates the utility of time series RADARSAT-1 Synthetic Apertu re Radar (SAR) to detect melt onset ( MO) and pond onset (PO) in the North Water (NOW) Polynya. SAR detected MO was associated with the approach of th e daily average near surface air temperature (T-air) toward freezing, the b eginning of a daily average surplus in the net all-wave radiation flux (Q*) , and a sharp decrease in the integrated shortwave albedo (alpha) at the su rface. Relationships between microwave scattering and air, snow surface and ice surface temperature, up until MO, proved sensitive to the diurnal acqu isition times of RADARSAT-1. Time series results demonstrate that, despite its uncalibrated status, RADARSAT-1 ScanSAR data unambiguously identifies M O and PO over landfast First-Year Ice (FYI) within the NOW Polynya. Spatial ly, results suggest a significantly earlier spring melt on the Greenland co ast compared to the Ellesmere coast (10 to 15 days for regions between 77 d egreesN and 79 degreesN and up to 45 days for regions between 76 degreesN a nd 77 degreesN). The regional near-surface air temperature pattern was cons istent with the spatial pattern of a SAR detected date of MO and PO.