Remote sensing of avalanches in northern Norway using Synthetic Aperture Radar

We present results from using synthetic aperture radar data (SAR) to analyse three avalanches in the county of Troms in northern Norway during the late snow season 2013. During a persistent polar low pressure activity at the end of March and the beginning of April 2013, inducing high precipitation 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 evacuations. 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 compared 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 delineated avalanches and outlines derived from optical data.