Assessment of surface melt with (In)SAR on Blue Ice Areas at the King Baudouin Ice Shelf

Abstract

Blue ice areas, are areas in Antarctica where, either due to local heat sources (areas with lower albedo and thus more absorption of shortwave radiation - i.e. Nunataks) or high windspeed, all the snow is melted or eroded away and the underlying (blue) ice is visible. This occurs often around the grounding line between the ice sheet and ice shelf. At this grounding line area, a micro climate exists above the blue ice, which increase surface melt, due to a combination of decreased albedo and warming due to the mixing of cold and warm air. Detection of surface melt on this blue ice is important because this warmer surface melt water results in the increase of hydrofracturing and as a result, the decrease of ice shelf stability. Radar imagery above snow areas is a effective method to detect surface melt, which also ensures a continuous data record. Above blue ice, this is continuous data record of surface melt is also desired, but not done yet and therefore the focus of this thesis is surface melt detection on blue ice with radar imagery. By using the method of Hui et al., 2014 to classify blue ice areas, it is shown that the blue ice area extent (non-stable blue ice) is increasing over the years in the peak of the melt season. However, the extent is slightly decreasing during the non-melt season (stable blue ice). The data of Sentinel-1B is used during the austral summer of 2017/2018, to detectsurface melt on blue ice. This is done via interferometry (and the corresponding coherence) and with the backscatter coefficient. Coherence turns out the be an unreliable method to detect surface melt, since the influence of wind and precipitation on the decrease of coherence is dominant. Thus, surface melt detection via this method is difficult. Backscatter showed some potential to detect surface melt on blue ice, but due to the larger standard deviation than the actual decrease of backscatter (assumed due to surface melt), a clear distinction between blue ice and surface melt can not be made. Melt features, such as rivers, lakes and ponds are detectable with the backscatter, due to their distinctive shape. Since these melt features are linked to surface melt, backscatter can indirectly be used to detect surface melt on blue ice.Applied Earth Science