High resolution radar imaging of snow avalanches

Abstract

Snow avalanches are a complex type of gravity driven mass-movement phenomena and can exhibit very different flow dynamics. They may flow as a dilute and fast powder snow avalanche, or cohesive snow may cause a dense and slow gliding motion. The current knowledge and understanding of the processes involved are partly limited due to the lack of high-resolution spatial measurements of full-scale avalanches. The diversity of avalanches is known from point measurements and deposits, but only radar can connect those observation spatially.

This thesis explores the newly developed radar sensor GEODAR. The radar signal can penetrate a powder cloud and measures reflections from the underlying denser flow structures. GEODAR allows us to track the evolution of flow features such as surges, flow regimes and transitions between them in time and space. In three chapters, I present interpretation of the GEODAR data and add greatly to the understanding of dynamic processes in snow avalanches.

In particular, I identify typical avalanche signatures in the radar data and classify the variety of avalanches in terms of seven flow regimes. I investigate in detail the influence of surges on the intermittent regime which is uniquely found in large powder snow avalanches. And in a third study, I analyse transitions between cold and warm flow regimes and explain the occurrence with the temperature of the snow cover.