Author: Zachary Keskinen

Detecting Avalanches from Space: When can we use Sentinel-1 imagery for debris identification?

Can we detect avalanche debris from space? Snow avalanche records have historically come from field observations and consequently been spatially and temporally limited. Remotely sensed avalanche observations show promise in providing more complete databases of avalanche observations. Sentinel-1 is a synthetic aperture radar (SAR) satellite that provides 10-meter resolution and has proven ability in identifying avalanche debris. (https://sentinel.esa.int/web/sentinel/missions/sentinel-1) As a SAR satellite Sentinel-1 can penetrate clouds and is unaffected by darkness. This allows for avalanche detections during storms and polar darkness. Previous research has focused on exploring automated detection methods, and mapping major avalanche cycles (https://www.mdpi.com/2072-4292/11/23/2863). An unexplored question is the primary controls on when an avalanche is detectable in Sentinel-1 imagery. Previous studies have shown a clear size constraint where the spatial resolution of Sentinel-1 is insufficient to resolve the avalanche debris (https://nhess.copernicus.org/articles/20/1783/2020/). This study explores not only this size controls on detections, but also avalanche type, local incidence angle, meteorological factors, and topographic effects. Methods Records of field observed avalanches from the Utah Department of Transportation and Bridger-Teton Avalanche Center provided locations, dates, and information on avalanches (Figure 1). Reported avalanches had a mean destructive size of 2.39 (standard deviation of 0.76) and were 93.5% dry, 93.3% slabs, and about half came from the Bridger-Teton dataset. Sentinel-1 intensity image pairs with the same orbital geometry were downloaded from prior to the avalanche cycle (reference image) and following the cycle (activity image). Changes in Sentinel-1 images were used to manually detect avalanche debris based on significant (2+dB) increase in backscatter in the track or runout of avalanche paths. Figure 2 shows a pair of intensity Sentinel-1 images with annotated criteria for detection. Potential controlling factors (type of avalanche, trigger, d-size, meteorological history (PRISM) and topographic effects) were extracted for each avalanche. Results 4 major avalanche cycles were manually detected

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