Item: Front and Internal Velocity Distribution in Powder Snow Avalanches
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Title: Front and Internal Velocity Distribution in Powder Snow Avalanches
Proceedings: International Snow Science Workshop 2016 Proceedings, Breckenridge, CO, USA
Authors:
- Jan-Thomas Fischer [ Austrian Research Centre for Forests - BFW, Innsbruck, Austria ]
- Anselm Köehler [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Andreas Kofler [ Austrian Research Centre for Forests - BFW, Innsbruck, Austria ]
- Betty Sovilla [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Jim McElwaine [ University of Durham, Durham, United Kingdom ]
Date: 2016-10-02
Abstract: Accurate velocity measurements of avalanches are essential for testing simulation tools and for performing risk mitigating studies. However, the flow of avalanches is complicated and not described by one unique velocity. In particular frontal approach velocities may not be representative for the internal flow dynamics. Furthermore measured velocities vary greatly not only with avalanche size and type but also with the instrument used. Optical methods, such as videogrammetry and photogrammetry can provide accurate measurements, but only of the outermost boundary and for large avalanches the inner core of the avalanche is nearly always concealed by a powder cloud. Radar of the appropriate wavelength can penetrate through the overlying cloud and directly measure this inner core, which is usually the most destructive part of the avalanche. In this work we investigate the velocity distribution of the inner avalanche core by combining radar data from two different systems, both installed at the Vallée de la Sionne avalanche test site, in Switzerland. Both systems operate at a frequency of 5-6 GHz which penetrates through the cloud and reflects of dense flow structures or lumps larger than around 50 mm. One radar is a phased array FMCW system, that can track fronts and internal surges with unprecedented spatial resolution but does not directly measure velocities. The other system is a pulsed Doppler system that directly measures velocity distributions in a coarse spatial resolution of around 50 m. By combining the data from both systems we can describe the velocity distribution along the length of the avalanche. Our measurements show that main material velocities in the avalanche head, can reach up to approximately two times the approach velocity.
Object ID: ISSW16_O9.04.pdf
Language of Article: English
Presenter(s):
Keywords: avalanche dynamics, radar measurement, velocity, avalanche head dynamics
Page Number(s): 218-221
Subjects: avalanche dynamics Doppler radar measurements avalanche velocity
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