Setting a speed trap for an avalanche
Snow avalanches and currents of gas and rock released by volcanic eruptions cause significant loss of life around the world. Understanding the dynamics of these flows is complex because the majority of the mass is in a thin granular layer that is often hidden by a cloud of suspended material. To determine the flow speed of the dense part of an avalanche, a new instrument has been developed and installed at a test site in Vallée de la Sionne in Switzerland. The results are being used to improve computer models for flow dynamics and therefore improve risk zoning in mountain areas.
The radar instrument is based on an FMCW phased array radar. The radar is mounted in an avalanche bunker and looks up the path. It has an operating frequency of 5.3GHz, which is a long enough wavelength to pass through the powder cloud and obtain an image of the denser layers of flowing snow beneath. The range of the instrument is over 2000m and the instrument extracts flow data from every 0.75m along the avalanche path 50 times a second, forming an animated record of the sub-surface flow of an avalanche event. The data produced provides real field data from natural and triggered avalanche events to unrivalled detail, helping to inform the flow laws and to better predict and accommodate such avalanche events in the future.