The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne

Köhler, Anselm; McElwaine, J. N.; Sovilla, Betty; Ash, Matthew; Brennan, Paul V.

doi:10.1002/2016jf003887

Cited by 38 publications

(101 citation statements)

References 36 publications

(51 reference statements)

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“…The original map is obtained from the Swiss Geoportal () in Swiss coordinate system CH1903 (SRID 21781). Figure reproduced from Köhler et al ().…”

Section: Methods and Datamentioning

confidence: 97%

“…The base band frequency is 5.3 GHz, and the corresponding wave length of around 57 mm is roughly the minimal object size providing reflection. Therefore, GEODAR only sees the denser flow structures below the dilute powder cloud (Köhler et al, ). A key feature of GEODAR is that it records the full chirp signal as a raw time domain signal.…”

Section: Methods and Datamentioning

confidence: 99%

“…Zero intensity corresponds to the background signal. Positive values quantify the reflection properties of the flow surface and dielectric changes throughout the flow height (Köhler et al, ). The avalanche front gives normally the strongest signal, and it appears as a strong step change in the range‐time diagram.…”

Section: Methods and Datamentioning

confidence: 99%

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GEODAR Data and the Flow Regimes of Snow Avalanches

Köhler

McElwaine

Sovilla³

2018

JGR Earth Surface

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GEOphysical flow dynamics using pulsed Doppler radAR (GEODAR), a custom radar system, images avalanches over the entire slope with high spatial and temporal resolution at the experimental test site Vallée de la Sionne in Switzerland. Between winter seasons 2009/2010 and 2014/2015, data have been acquired from 77 avalanches. These data sets describe a wide variety of avalanches, which we classify in terms of seven flow regimes and combinations thereof. These flow regimes expand on previous classifications, with four identifiable dense flow regimes (where interaction between granules and with the flow bed dominates dynamics) and two different dilute flow regimes (where interaction between snow particles and the air becomes dominant). There is a further regime identified where snow balls simply roll down the mountain. A cold dense regime and a warm shear regime behave like noncohesive granular flows with velocity shear throughout the flow. A sliding slab regime and a warm plug regime occur when cohesion dominates and causes the flow units to act as solid‐like objects sliding on a thin shear zone. An intermittent regime connects the cold dense regime with the suspension regime and is characterized by highly fluctuating density and surging activity. GEODAR enables localization of these flow regimes and transitions between them in time and space. We discuss flow regime transitions in terms of snow properties, topography, speed, and size of the avalanches. This paper also serves as a reference for the data set which is made publicly available and should prove to be an invaluable resource for the development of physically based avalanche models.

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“…The original map is obtained from the Swiss Geoportal () in Swiss coordinate system CH1903 (SRID 21781). Figure reproduced from Köhler et al ().…”

Section: Methods and Datamentioning

confidence: 97%

Section: Methods and Datamentioning

confidence: 99%

See 1 more Smart Citation

GEODAR Data and the Flow Regimes of Snow Avalanches

Köhler

McElwaine

Sovilla³

2018

JGR Earth Surface

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“…Therefore,to show the functionality and the capability of the proposed phased array antenna to produce high resolution image of the snow avalanche, the preliminary results from the large avalanche which was artificially triggered triggered on 18th of January 2016 is presented. The data processing steps which include chirp extraction, spectrum calculation and moving target identification (MTI) are described in detail in [24]. The MTI is shown in dB normalized to the MTI background.…”

Section: A Full-scale Avalanche Resultsmentioning

confidence: 99%

Overlapped Phased Array Antenna for Avalanche Radar

Tanha

Brennan

Ash

et al. 2017

IEEE Trans. Antennas Propagat.

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract-Snow avalanche is a natural phenomenon, which annually causes infrastructure damage and leads to human casualties in many countries all over the world. As a result, a detailed hazard mapping is required to be able to understand the avalanche risk levels. Also, the scarcity of the areas suitable for constructing infrastructures in the mountains places a high premium on providing high precision hazard mapping. This paper presents the design and development of an advanced phased array antenna for an FMCW radar to produce a high resolution image of snow avalanche in range and cross-range. The proposed antenna is a 16-element fully populated phased array with ±14 • azimuth beamwidth and ±22.5 • fixed elevation angle. The designed phased array antenna has 14.4dBi gain and -20.3dB sidelobe level. In this design Subarraying overlapping technique has been used to eliminate undesirable grating lobes by means of spatial anti-alias filtering. A phased array power divider is proposed to allow tapering of the amplitude of the elements to achieve low sidelobe level.

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“…The lower left panel shows a detail of the frontal dynamics of a large powder snow avalanche released at Vallée de la Sionne in 2017 (Photo: Yann Gross). The lower middle panel shows a detail of the avalanche frontal region measured with GEODAR in 2015 (Köhler et al, ). Both pictures show a complex surging activity in the avalanche frontal zone.…”

Section: Introductionmentioning

confidence: 99%

The Intermittency Regions of Powder Snow Avalanches

Sovilla¹,

McElwaine

Köhler³

2018

JGR Earth Surface

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Powder snow avalanches are typically composed of several regions characterized by different flow regimes. These include a turbulent suspension cloud of fine particles, a dense basal flow, and an intermittency frontal region, which is characterized by large fluctuations in impact pressure, air pressure, velocity, and density, but whose origin remains unknown. In order to describe the physical processes governing the intermittency region, we present data from four large powder snow avalanches measured at the Vallée de la Sionne test site in Switzerland, which show that the intermittency is caused by mesoscale coherent structures. These structures have a length of 3–14 m and a height of 10 m or more. The structures can have velocities as much as 60% larger than the avalanche front speed and are characterized by an air/particle mixture whose average density can be as high as 20 kg/m3. This average density increases the drag on large granules by a factor of up to 20 compared to pure air, so that each structure can maintain denser snow clusters and single snow granules in suspension for several seconds. The intermittency region has importance for the dynamics of an avalanche, as it provides an efficient mechanism for moving snow from the dense layer to the powder cloud, but also for risk assessment, as it can cause large forces at large heights above the basal dense layer.

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The dynamics of surges in the 3 February 2015 avalanches in Vallée de la Sionne

Cited by 38 publications

References 36 publications

GEODAR Data and the Flow Regimes of Snow Avalanches

GEODAR Data and the Flow Regimes of Snow Avalanches

Overlapped Phased Array Antenna for Avalanche Radar

The Intermittency Regions of Powder Snow Avalanches

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