Flowing from release to runout: High-resolution radar measurements of snow avalanches

8 S.

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200212316

ISSW 2024: Proceedings of the International Snow Science Workshop 2024 Tromsø, Norway (2024) , 8 S.

Radar technology is indispensable in the context of snow avalanche monitoring. Practitioners rely on the capabilities of related real-time detection systems while scientists use radar for high resolution measurements. In combination with other measurement systems, radar provides an important reference: For example, neither in-flow nor single point measurements can be solely used to interpret the avalanche flow evolution in a holistic view without the reference that radar systems provide. Radar data yield a multitude of details from release to avalanche flow and final deposition. Today, this information is rarely used in practice as the processing requires manual steps but is invaluable from a scientific point of view. We present radar data of the newly developed frequency modulated radar mGEODAR, which is deployed at the Nordkette test-site above Innsbruck, Austria, and recorded data on nearly 200 avalanches since 2021. The avalanches range from very small to large size and corresponding flow regimes are mostly dry-dense with the largest ones reaching the transition towards powder snow avalanche flow. During the release, the radar’s high spatial and temporal resolution allows us to infere weak layer crack propagation speeds in the context of snow slab avalanche initiation after an artificial trigger. We obtained crack propagation speeds in the up-slope and downslope directions up to 100m/s, which is in line with the recent literature values measured from camera-based full-scale slab avalanches and numerical modeling of propagation saw tests. During the flow phase, we track the evolution of the avalanche front velocity that typically reaches up to 30m/s, and show the application of the front data for avalanche flow model evaluation. Especially during the deposition, the radar signatures allow
to distinguish the stopping behavior and to differentiate between cold and warm flow regimes. The presented
radar datasets provide a valuable source for future research covering the improvement of automatic and
machine learning supported classification, filtering and spectral processing, as well as snow and avalanche
science related research questions regarding the avalanche flow evolution and dependence on weather and
snowpack patterns.
Keywords: Avalanche dynamics, radar measurements, weak layer crack propagation speed, front velocity