Tapping the potential of multi-temporal thermal infrared UAV over a debris-covered glacier 

Understanding the role and dynamics of debris covering alpine glaciers is complex and multi-faceted. A thin or non-continuous layer (smaller than 2cm) promotes melting, whereas a thicker layer insulates the underlying ice. The response of debris-covered glaciers to climate change is not uniform worldwide. These glaciers not only react to the changing climate, but they are also sensitive to debris-cover evolution. To date, studies analysed limited spatio-temporal data and thus do not describe multi-temporal changes in debris cover thickness. However, these strongly impact long-term glacier evolution as topography changes can lead to ice cliff formation, which is known to considerably speed up glacier melt. Multi-temporal high-resolution remote sensing offers the possibility to fill this gap and monitor changes at a small scale. In this contribution, we apply multi-temporal close-range remote sensing to a debris-covered glacier in the Swiss Alps (Zmuttgletscher, Valais, CH). We make use of Unmanned Aerial Vehicle (UAV) surveys equipped with a dual optical-thermal camera together with manual debris excavations and in-situ meteorological data in different years (2020 and 2023). The thermal surveys are calibrated using supraglacial and proglacial lake water temperatures, combined with debris surface temperature measurements. We explore the debris thickness, morphology, and topography evolution of a portion of the glacier, and discuss it in relation to glacier dynamics and debris transport. The work contributes to the understanding of glacier debris evolution, which is often neglected in debris-covered glacier models and global projections.