Monitoring the Terra Nova Bay polynya by MODIS ice surface temperature imagery during winter 2010 and 2011

Polynyas occur in remote, mostly inaccessible, places of the Arctic and Antarctic. Hence, remote sensing is essential for monitoring their dynamics. On regional scales, passive microwave (PM) radiometers provide useful information about their extent because they are available on a daily basis and do not depend on daylight and penetrate perfectly through clouds. Nonetheless, the coarse resolution of PM radiometers does not allow an accurate discrimination of open water and thin ice from thick ice. Synthetic radar aperture (SAR) sensors provide a better spatial resolution (up to few tents of meters) but present a lower data acquisition frequency. Despite their sensitivity to the presence of clouds, thermal infrared (TIR) Moderate Resolution Imaging Spectroradiometers (MODIS) operate at large swath widths providing high spatial resolution images (typically 1 Km) several times per day. Many studies already demonstrated their usefulness for the retrieval of polynyas size and thin ice thickness. In this study, we deal with MODIS observation of a frequently occurring coastal polynya in the Terra Nova Bay (TNB), located in the western Ross Sea (Antarctica). We examine the TNB polynya evolution during the freezing seasons (April to October) 2010 and 2011 using a new methodology that combines a sequence of MODIS swath-based scenes (level-1b products). Not-informative cloudy scenes have been completely discarded from our analyses Clear-sky and fog-contaminated scenes have been analysed in order to extract the polynya area, thus having a revisit time of few hours in absence of thick clouds. Results have been validated through the comparison with a huge set of ENVISAT ASAR images. The good agreement with high resolution ASAR information demonstrated the potential of this tool for the continuous monitoring of the polynya extent. A comparison with TNB polynya extent estimations retrieved by other MODIS and PM based tools has also been carried out for freezing season 2010 and 2011, and differences discussed. Finally, wind speeds and directions measured by automatic weather stations located along the TNB coast, have been used to identify katabatic events to be compared with the polynya dynamics during the study period.