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Radar backscatter analysis and change detection
Snow avalanche detection from the change in SAR backscatter coefficient based on two satellite images taken before and after the release.
Utilizing the change in SAR backscatter coefficient over time, snow avalanches can be detected on daily basis in Norway (Figure 2). These daily detections are used by the Norwegian Avalanche Forecasting Service hosted by the Norwegian Water and Energy Resource Directorate (NVE) (www.satskred.nve.no) in their avalanche forecasting work.
The presence of wet snow can be important during several avalanche hazards (e.g. normal snow avalanches, slush avalanches, landslides). NORCE has a long history of using SAR to detect wet snow and has developed operational processing chains. A current focus is on long term mapping of wet snow on Svalbard related to rain-on-snow events and avalanche hazards. Snow depth or Snow Water Equivalent (SWE) are important parameters for snow avalanche release. NORCE has several projects where we focus on these parameters both with satellite and airborne radars.
NORCE has developed a Ground Penetrating Radar (GPR) that can be flown on drones (Figure 3). It is capable of measuring snow depth and layering valuable for avalanche hazard assessment. The GPR can be used to measure snow water equivalent (SWE), detect people buried in avalanches and study the soil properties by analyzing the differential wave penetration.
Ground Penetrating Radar mounted on drone for the measurement of snow properties and depth.
Radar backscatter is sensitive to Soil Moisture Content (SMC) and can be derived from SAR images. NORCE has an ongoing project where we try to establish several methods to derive SMC. Both relative methods (scaling backscatter) and absolute methods where we invert physical models for backscatter are considered.
Monitoring of hazards related to dams and water reservoirs can be done using SAR to measure lake extent and level. Monitoring of glacier limited lakes and outbursts (for example Jökullaup) can also be done. NORCE has long term expertise in flood monitoring using SAR. Floods can in some cases be a consequence of avalanche release (e.g. rock avalanches or avalanches that are released in rivers and cause river outburst).
SAR backscatter is to some extent sensitive to freezing/thawing of the top layer of the soil, which is especially important in the dynamics of permafrost areas and can play a role in avalanche release. NORCE has also tested out several methods to study the quick clay avalanche in Gjerdrum 2020. Slush avalanches have also been studied, but only large avalanches are detectable.
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