Tracking Snow Avalanches: Integrating Field Observations and Satellite-Derived Indicators

Abstract. In this study, we integrated information from the French avalanche database, high-resolution digital elevation models (DEMs), and Sentinel-1 SAR images to model avalanche extents for events occurring across three distinct time periods in three French massifs. The modelled avalanche extents were compared with manually delineated polygons mapped over SAR RGB composites generated using the principles applied in colour-based change-detection algorithms. The comparison revealed strong correspondence between the two independent approaches, with IoU values ranging from 0.42 to 0.47 and F1 scores from 0.58 to 0.63 across the different massifs. We further analyzed the distribution of SAR backscatter values in pre- and post-event images across different zones of the avalanche paths. The results indicated that a fixed 3 dB threshold would most likely be insufficient to capture the full avalanche extent, as some zones showed backscatter increases of less than 3 dB in post-event SAR imagery. As a result, a multi-threshold approach based on different avalanche zones is recommended. Finally, we assessed the potential of Sentinel-2 optical imagery to detect surface changes and characterize the physical behaviour of avalanche-affected paths following intense avalanche events. However, the results were inconsistent, showing the expected trends in one study area but nearly opposite patterns in the other, suggesting that integrating optical data for automated avalanche mapping may not always be reliable.