Analysis of ablation areas in Antarctica through remote sensing

The PhD thesis intends to study and map those areas in Antarctica involved in surficial ablation processes linked to the wind action (wind-scouring phenomenon, i.e., erosion and sublimation of snow and ice for the effect of katabatic winds). In fact, Antarctica shows a meanly positive mass balance and the analysis of ablation areas, which can show near-zero or negative surface mass balance in the case of glazed snow and blue ice respectively, becomes fundamental since an eventual expansion would have consequences also on continental mass balance, leading to effects on sea-level rise. To glazed snow and blue ice, the study of snow megadunes is added, since these landforms are associated to the presence of glazed snow (characterizing their leeward flanks) and they present m/km variations leading to impacts on snow accumulation processes. All these surfaces and landforms optically behave differently to surrounding snow, the main surface of Antarctica, showing a lower albedo and so can be investigated from the space. Therefore, remote sensing, i.e., the study of globes through satellite imagery, has a key role in this research project and allows mapping and temporal-spatial analyses of these areas. Albedo was analysed using both already available data of Moderate Resolution Imaging Spectroradiometer (MODIS) and data that needed different calibration steps, i.e., Landsat-mission imagery. In the second case, a new model for its calculation was validated for broadband albedo and is under evaluation for narrowband albedo. MODIS was used for determining blue ice optical properties, which show an albedo of 0.50-0.70 and Landsat instead was applied in snow-glazed analyses, as its higher spatial resolution allowed to detect the slightly lower albedo that these surfaces have in respect to surrounding snow (maximum -0.04 in near-infrared wavelengths). Additionally, the other investigated meteorological parameters were wind, which can be studied using reanalysis atmospheric models or using a model derived from sastrugi (peculiar landforms parallel to prevailing wind direction) and thermal brightness temperature (from Landsat 8 TIRS). The use of these parameters allowed the automatic mapping of both glazed snow and blue ice, leading to their spatial and temporal analyses. Finally, the morphological analyses of megadunes provided the most relevant results of the thesis, confirming through a comparison of in-situ GPS/GPR measurements (It-ITASE traverse of 1999) and remote data (REMA DEM), their “antidunal” formation and allowing to precisely quantify their migration. These results were furtherly supported through an analysis of feature tracking on Landsat and Sentinel-2 images, which provided analogous results. In conclusion, this PhD thesis provides new and significant information about the ablation areas in Antarctica, as well as confirms and quantifies what was previously hypothesized. This information will be of fundamental importance for surface mass balance studies and for a better understanding of the role of Antarctica on the global climatic system.