ALL EYES ON GLACIERS: REMOTE SENSING OF THE CRYOSPHERE

Remote sensing has become an invaluable tool for glaciologists. The keys to its success are the ability to repeatedly monitor small to large, often inaccessible areas and quickly process data through the integration in geographical information system (GIS) environments. From aerial photography in the early days, remote sensing has evolved owing to the ever-increasing input of large amounts of data from satellite platforms, while traditional photogrammetric techniques are now experiencing a renaissance thanks to the growing importance of UAVs and terrestrial photography. This Ph.D. thesis explores remote sensing applications for cryospheric monitoring and is aimed at improving our understanding of processes of glacier retreat, energy budget, mass balance and dynamics and of snow cover variability, using a variety of sensors (optical and thermal cameras, laser scanners) and platforms, including satellites, planes and unmanned aerial vehicles (UAVs). Each chapter of the thesis presents a case study: • The creation of an inventory of glaciers and potentially dangerous glacial lakes of the Central Karakorum National Park, Pakistan (Chapter 3) using Landsat satellite data. Both glaciers and lakes are very important to monitor as they are both a source of water and a potential hazard in the area. • The analysis of thickness changes and hazards related to the downwasting and collapse of Forni Glacier, a large glacier in the Italian Alps, through a combination of approaches, i.e. Laser scanner, UAV and terrestrial photogrammetry (Chapter 4). • The spatial distribution of glacier albedo (Chapter 5), important to estimate ice and snow melt for a large valley glacier in the Italian Alps (Forni Glacier) validating a pre-existing methodology using Landsat satellite data • The evolution of glacier albedo through time (chapter 6) for a selection of glaciers in the Italian Alps, Ortles-Cevedale group, extending the approach described in chapter 5, to understand the extent of glacier darkening and the potential causes. • The evolution of supraglacial debris cover for a selection of glaciers in the Italian Alps, Ortles-Cevedale group (chapter 7) using aerial orthoimagery. This analysis is fundamental to model the melt of debris covered glaciers and understand their evolution. • The structural evolution of the glacier tongue of a large valley glacier (Forni Glacier) using aerial and UAV imagery, to investigate the changes in glacier dynamics over time (Chapter 8). • The analysis of multiannual variability of snow cover in a large river basin of Central Asia (Upper Irtysh, Kazakhstan) and the relationship between snow cover depletion and atmospheric circulation indices using MODIS satellite data (Chapter 9), to provide useful tools for flood forecasting. The key findings from Chapters 4 to 8 permit to assess the evolution of a wide glacier area of the Italian Alps, highlighting the increase in supraglacial debris cover and related decrease in glacier albedo, increased rates of glacier downwasting and structural collapse, increasing the potential for glacier hazards. The analysis of glacier hazards was also an important part of the CKNP study, including an assessment of the current state of glaciers and glacial lakes. The focus on snow cover variability in Central Asia shows instead the importance of atmospheric circulation and the possibility of long-term forecasts using widely available teleconnection indices. Most relevant processes in the cryosphere were touched upon in this thesis, from accumulation processes (i.e. snow cover), to melt (including albedo and debris cover which influence it) and structural characteristics. Furthermore, while the case studies can be read as independent units, all the methodologies presented here transcend the single example and are widely applicable to different glaciers or areas. In particular, glacier albedo or debris cover maps are an essential input to improve glacier melt models, and could be used in the CKNP to model melt more accurately. Glacier mass balance and dynamics could also be monitored more accurately and at unprecedented spatial resolution using UAVs.