Remote Sensing of Avalanches in Northern Norway Using Synthetic Aperture Radar

We present results from using synthetic aperture radar data (SAR) to analyse three ava- lanches in the county of Troms in northern Norway during the late snow season 2013. During a persis- tent polar low pressure activity at the end of March and the beginning of April 2013, inducing high pre- cipitation rates in combination with high wind speeds, an extensive avalanche cycle took place in that area. Several avalanches released naturally causing fatalities, road closures and community evacua- tions. The main goal of our study was to investigate whether high resolution SAR could be used for detecting avalanche debris in the run-out zones. For validation purposes we used, among others, a high resolution camera operated on an Unmanned Airborne Vehicle (UAV) to acquire very accurate ortho-photos of the avalanches. The UAV-maps were of unprecedented resolution (~5 cm). The result of the analysis of the high resolution Radarsat-2 image showed that avalanches could be identified visually due to the high contrast between low radar backscatter from unperturbed snow and high backscatter (caused by increased surface roughness/snow mass) of the avalanche debris in the avalanche run-out zones. In order to assess the accuracy, the avalanche delineations were com- pared with results from UAV photos and photographs taken during helicopter reconnaissance flights right after the events. In two of three cases, a good correspondence was found between SAR deline- ated avalanches and outlines derived from optical data.