High resolution observations of the Terra Nova Bay polynya using COSMO-SkyMed X-SAR and other satellite imagery

摘要

In this study we analysed a combination of high and coarse resolution X-band COSMO-SkyMed Synthetic Aperture Radar (SAR) scenes collected during two periods in July and September 2011 over the Terra Nova Bay (Antarctica). High resolution (5m per pixel) and lower resolution SAR (100m) acquired over intervals of the order of minutes provided both, fine details and a full large-scale view of the polynya. The analysis was supported by several Ice Surface Temperature (IST) maps per day obtained from the thermal band of Moderate Resolution Imaging Spectroradiometer (MODIS) and some additional C-band Envisat Advanced SAR (ASAR) scenes available during the July period. The dataset revealed two major openings around 2000km~2 occurred in the July period and one opening around 2500km~2 in the September period. The SAR analysis revealed that the polynya area is clearly distinguished from the sea ice pack offshore during the growing and closing phase. During the opening phase, the open polynya area was characterized by newly formed frazil ice organized as ice streaks parallel to the wind direction and separated by a distance of between 300 and 800m. Waves of length between 30 and 70m were noted on the streaks of frazil ice and on the frazil and grease ice accumulated at the polynya border. The early stage of the growing phase was indicated by the uniform distance of the ice streaks near the border of the polynya, while convergence was an indication that the wind was slowing down and that the growing phase was at a late stage. The closing phase was characterized by the progressive freezing of the open polynya area from the downwind border toward the coast. The results of this analysis suggest that the detection of the polynya area from thermal infrared or microwave temperatures is more effective during the growing phase, when large areas of unfrozen water are present within the polynya, than during the closing phase when large areas of thin sea-ice prevail.