UAV-based thermal mapping for interpreting geomorphological processes in complex alpine environments

As a result of climate change, temperatures in the European Alps are rising twice as fast compared to the global average, leading to unprecedented glacier retreat. Deglaciating alpine landscapes are considered extremely dynamic, evolving rapidly over space and time. One of the legacies of glacial activity is buried ice, also known as legacy or dead ice, describing ice that survives in the proglacial area for years to decades after glaciers retreat due to isolation from solar radiation and thermal effects by a sediment cover. Buried ice plays an important role in alpine basins, for instance, by providing long-term water storage. It is also likely to be an important influence on geomorphic processes, such as erosion. Quantification of erosion and deposition patterns from DEMs of difference (DoDs) may be problematic if DoDs do not distinguish geomorphic change from buried ice melt out. Such distinction is commonly omitted in studies, as ground-based geophysical measurements (e.g. Electrical Resistance Tomography, ERT) may need to be applied, extremely difficult given the challenges associated with accessing steep alpine terrain and the spatially extensive areas that may need to be measured. The extent of buried ice is therefore likely to be poorly estimated.

Satellite-based thermal remote sensing may provide a solution to this problem. Indeed, as an example, Interferometric SAR may be used to detect to a very high vertical precision the surface changes that suggest buried ice. However, the spatial resolution of such data may be inefficient when the surface changes are complex. Recent developments in drones and thermal sensors include compact drones with high quality thermal sensors, such as the DJI Mavic 3T. Drones have the benefit of (1) providing a higher spatial resolution compared to satellite thermal remote sensing, and (2) covering larger areas, compared to existing methods of buried ice detection, such as ERT.

In this research, a thermal drone was tested to identify buried ice in the Turtmann basin, a rapidly deglaciating Alpine valley in the Canton of Valais (southwestern Switzerland). Areas known to contain buried ice were surveyed. The assessment of the thermal images showed high coherence between cold patches on the images with known presence of buried ice.

This study highlights the potential for thermal drones in assessing and monitoring geomorphological processes in deglaciating environments, with a specific focus on buried ice. The results provide guidelines on equipment, survey design and execution, as well as data analysis for the use of thermal drones in alpine environments. Future research could focus on identifying approaches for validating the method for surveying areas with no prior knowledge on buried ice. There is a huge potential for the use of thermal drones that is yet to be explored.