On the estimation of spring melt in the North Water polynya using RADARSAT‐1

Abstract This paper evaluates the utility of time series RADARSAT‐1 Synthetic Aperture 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 the daily average near‐surface air temperature (Tair) toward freezing, the beginning of a daily average surplus in the net all‐wave radiation flux (Q*), and a sharp decrease in the integrated shortwave albedo (α) at the surface. Relationships between microwave scattering and air, snow surface and ice surface temperature, up until MO, proved sensitive to the diurnal acquisition times of RADARSAT‐1. Time series results demonstrate that, despite its ‘uncalibrated’ status, RADARSAT‐1 ScanSAR data unambiguously identifies MO and PO over landfast First‐Year Ice (FYI) within the NOW Polynya. Spatially, results suggest a significantly earlier spring melt on the Greenland coast compared to the Ellesmere coast (10 to 15 days for regions between 77°N and 79°N and up to 45 days for regions between 76°N and 77°N). The regional near‐surface air temperature pattern was consistent with the spatial pattern of a SAR detected date of MO and PO.