scholarly journals Estimation of Avalanche Development and Frontal Velocities Based on the Spectrogram of the Seismic Signals Generated at the Vallée de la Sionne Test Site

Geosciences ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 113 ◽  
Author(s):  
Emma Suriñach ◽  
Elsa Leticia Flores-Márquez ◽  
Pere Roig-Lafon ◽  
Glòria Furdada ◽  
Mar Tapia
Keyword(s):  
Doppler Radar ◽  
Test Site ◽  
Polar Coordinates ◽  
Measured Signal ◽  
Seismic Signals ◽  
Snow Avalanches ◽  
Signal Onset ◽  
Theoretical Function ◽  
Wet Snow ◽  
Radar Measurements

The changes in the seismic signals generated by avalanches recorded at three sites along a path at the Vallée de la Sionne (VdlS) experimental site are presented. We discuss and correlate the differences in the duration, signal amplitudes, and frequency content of the sections (Signal ONset (ON), Signal Body (SBO), and Signal TAil and Signal ENd STA-SEN) of the spectrograms with the evolution of the powder, transitional and wet snow avalanches along a path. The development of the avalanche front was quantified using the exponential function in time F (t) = K’ exp (β t) fitted to the shape of the signal ONset (SON section of the spectrogram. The speed of the avalanche front is contained in β. To this end, a new method was developed. The three seismic components were converted into one seismic component (FS), when expressing the vector in polar coordinates. We linked the theoretical function of the shape of the FS-SON section of the spectrogram to the numerical coefficients of its shape after considering the spectrogram as an image. This allowed us to obtain the coefficients K’ and β. For this purpose, the Hough Transform (HT) was applied to the image. The values of the resulting coefficients K’ and β are included in different ranges in accordance with the three types of avalanche. Curves created with these coefficients enable us to estimate the development of the different avalanche types along the path. Our results show the feasibility of classifying the type of avalanche through these coefficients. Average speeds of the avalanches approaching the recording sites were estimated. The speed values of wet and transitional avalanches are consistent with those derived from GEODAR (GEOphysical Doppler radAR) measurements, when available. The absence of agreement in the speed values obtained from seismic signals and GEODAR measurements for powder snow avalanches indicates, for this type of avalanche, a different source of the measured signal. Hence, the use of the two measuring systems proves to be complementary.

scholarly journals Measured shear rates in large dry and wet snow avalanches

2009 ◽  
Vol 55 (190) ◽  
pp. 327-338 ◽  
Author(s):  
Martin Kern ◽  
Perry Bartelt ◽  
Betty Sovilla ◽  
Othmar Buser
Keyword(s):  
Optical Sensors ◽  
Test Site ◽  
Snow Avalanches ◽  
Coherent Signals ◽  
Mean Velocity ◽  
Shear Rates ◽  
Wet Snow ◽  
The Mean ◽  
Time Lagged ◽  
Real Scale

AbstractWe present estimates of internal shear rates of real-scale avalanches that are based on velocity measurements. Optical velocity sensors installed on the instrument pylon at the Swiss Vallée de la Sionne test site are used to measure flow velocities at different flow heights of three large dry and wet snow avalanches. Possible sources of error in the correlation analysis of the time-lagged reflectivity signals measured by optical sensors are identified for real-size avalanches. These include spurious velocities due to noise and elongated peaks. An appropriate choice of the correlation length is essential for obtaining good velocity estimates. Placing restrictions on the maximum possible accelerations in the flow improves the analysis of the measured data. Coherent signals are found only in the dense flowing cores. We observe the evolution of shear rates at different depths between the front and tail of the flowing avalanche. At the front, large shear rates are found throughout the depth; at the tail, plug flows overriding highly sheared layers near the bottom of the flow are observed. The measured velocities change strongly with height above the ground and fluctuations around the measured mean velocity can be identified. We find that the dense flows are laminar, undergoing a transition from supercritical to subcritical flow behaviour from the head to the tail. Furthermore, we provide real-scale experimental evidence that the mean shear rate and the magnitude of velocity fluctuations increase with the mean discharge.

Comparison of the application of the Hough Transform method (characterization of the SON section in seismic spectrograms) at two different sites (VdlS and Ryggfonn) to study the evolution of avalanches.

2020 ◽  
Author(s):  
Emma Suriñach ◽  
Elsa Leticia Flores-Márquez
Keyword(s):  
Data Processing ◽  
Hough Transform ◽  
Seismic Signals ◽  
Snow Avalanches ◽  
Experimental Site ◽  
Transform Method ◽  
Wet Snow ◽  
Topographic Characteristics ◽  
A Site

<p>Recently, a method applying the Hough Transform was used to obtain the numerical parameters of the shape of the SON section of the spectrograms  of the seismic signals generated by snow avalanches at the experimental site of Vallée de la Sion (VdlS, Valais, Switzerland) (SFL, Davos). The avalanches were of different size and type (powder-snow, transitional and wet-snow) descending along the same path and recorded at two different locations 690 m of distance between them on the path. This helped us to estimate the evolution of the avalanche speed along the path from the starting zone to the run-out zone. We obtained different spectrogram definition parameters according to the type of avalanche.</p><p>We apply the same methodology to the seismic signals generated by avalanches at the Ryggfonn experimental site (NGI, Oslo). The avalanches were dry/mixed and dry/dense and occurred in the period (2004-2008). They were recorded in a site along the path. The instrumental conditions, characteristics of the raw data, and the data processing were like those of VdLS. However, the topographic characteristics of the site were different. At the Ryggfonn site, the distance between the starting zone and the sensor was 1640 m (985 in VdlS) and the vertical drop was 800 m (700 m in VdLS).</p><p>We present and compare the results obtained to validate a possible application of the method used to VdlS to other places and topographic conditions.</p><p>This research was funded by the CHARMA (CGL2013–40828–R) and the PROMONTEC projects (CGL2017-84720-R) of the Spanish Ministry of Economy, Industry and Competitiveness (MINEICO-FEDER) and RISKNAT group (2014GR/1243).</p>

scholarly journals The Coplane Analysis Technique for Three-Dimensional Wind Retrieval Using the HIWRAP Airborne Doppler Radar

2015 ◽  
Vol 54 (3) ◽  
pp. 605-623 ◽  
Author(s):  
Anthony C. Didlake ◽  
Gerald M. Heymsfield ◽  
Lin Tian ◽  
Stephen R. Guimond
Keyword(s):  
Global Optimization ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Optimization Method ◽  
Vertical Wind ◽  
Wind Component ◽  
Global Optimization Method ◽  
Analysis Technique ◽  
Radar Measurements ◽  
Cross Track

AbstractThe coplane analysis technique for mapping the three-dimensional wind field of precipitating systems is applied to the NASA High-Altitude Wind and Rain Airborne Profiler (HIWRAP). HIWRAP is a dual-frequency Doppler radar system with two downward-pointing and conically scanning beams. The coplane technique interpolates radar measurements onto a natural coordinate frame, directly solves for two wind components, and integrates the mass continuity equation to retrieve the unobserved third wind component. This technique is tested using a model simulation of a hurricane and compared with a global optimization retrieval. The coplane method produced lower errors for the cross-track and vertical wind components, while the global optimization method produced lower errors for the along-track wind component. Cross-track and vertical wind errors were dependent upon the accuracy of the estimated boundary condition winds near the surface and at nadir, which were derived by making certain assumptions about the vertical velocity field. The coplane technique was then applied successfully to HIWRAP observations of Hurricane Ingrid (2013). Unlike the global optimization method, the coplane analysis allows for a transparent connection between the radar observations and specific analysis results. With this ability, small-scale features can be analyzed more adequately and erroneous radar measurements can be identified more easily.

Numerical simulations of wet snow avalanches: interplay between cohesion and friction

2021 ◽  
Author(s):  
Guillaume Chambon ◽  
Thierry Faug ◽  
Mohamed Naaim
Keyword(s):  
Numerical Simulations ◽  
Flow Regimes ◽  
Liquid Water Content ◽  
Snow Avalanches ◽  
Shallow Flow ◽  
Distinctive Features ◽  
Wide Range ◽  
Wet Snow ◽  
Sensitivity Studies ◽  
Avalanche Flow

<p>Wet snow avalanches present distinctive features such as unusual trajectories, peculiar deposit shapes, and a rheological behavior displaying a combination of granular and pasty features depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) flow regimes can also occur during a single avalanche flow. In an attempt to account for this complexity, we report on numerical simulations of avalanches using a frictional-cohesive rheology implemented in a depth-averaged shallow-flow model. Through extensive sensitivity studies on synthetic and real topographies, we show that cohesion plays a key role to enrich the physics of the simulated flows, and to represent realistic avalanche behaviors. First, when coupled to a proper treatment of the yielding criterion, cohesion provides a way to define objective stopping criteria for the flow, independently of the issues incurred by artificial diffusion of the numerical scheme. Second, and more importantly, the interplay between cohesion and friction gives raise to a variety of nontrivial physical effects affecting the dynamics of the avalanches and the morphology of the deposits. The relative weights of frictional and cohesive contributions to the overall stress are investigated as a function of space and time during the propagation, and related to the formation of specific features such as lateral levées, hydraulic jumps, etc. This study represents a first step towards robust avalanches simulations, spanning the wide range of possible flow regimes, through shallow-flow approaches. Future improvements involving more refined cohesion parameterizations will be discussed.</p>

NSSL Dual-Doppler Radar Measurements in Tornadic Storms: a Preview

1975 ◽  
Vol 56 (5) ◽  
pp. 524-526 ◽  
Author(s):  
Rodger A. Brown ◽  
Donald W. Burgess ◽  
John K. Carter ◽  
Leslie R. Lemon ◽  
Dale Sirmans
Keyword(s):  
Doppler Radar ◽  
Radar Measurements ◽  
Tornadic Storms ◽  
Dual Doppler Radar

scholarly journals Modelling the system behaviour of wet snow avalanches using an expert system approach for risk management on high alpine traffic roads

2005 ◽  
Vol 5 (6) ◽  
pp. 821-832 ◽  
Author(s):  
A. Zischg ◽  
S. Fuchs ◽  
M. Keiler ◽  
G. Meißl
Keyword(s):  
Risk Management ◽  
Fuzzy Logic ◽  
Expert System ◽  
Temporal Variability ◽  
Hazard Index ◽  
Rule Base ◽  
Spatial And Temporal Variability ◽  
Snow Avalanches ◽  
System Behaviour ◽  
Wet Snow

Abstract. The presented approach describes a model for a rule-based expert system calculating the temporal variability of the release of wet snow avalanches, using the assumption of avalanche triggering without the loading of new snow. The knowledge base of the model is created by using investigations on the system behaviour of wet snow avalanches in the Italian Ortles Alps, and is represented by a fuzzy logic rule-base. Input parameters of the expert system are numerical and linguistic variables, measurable meteorological and topographical factors and observable characteristics of the snow cover. Output of the inference method is the quantified release disposition for wet snow avalanches. Combining topographical parameters and the spatial interpolation of the calculated release disposition a hazard index map is dynamically generated. Furthermore, the spatial and temporal variability of damage potential on roads exposed to wet snow avalanches can be quantified, expressed by the number of persons at risk. The application of the rule base to the available data in the study area generated plausible results. The study demonstrates the potential for the application of expert systems and fuzzy logic in the field of natural hazard monitoring and risk management.

Side-looking ADCP and Doppler radar measurements across a coastal front

2000 ◽  
Vol 25 (4) ◽  
pp. 423-429 ◽  
Author(s):  
C.L. Trump ◽  
N. Allan ◽  
G.O. Marmorino
Keyword(s):  
Doppler Radar ◽  
Radar Measurements ◽  
Coastal Front

scholarly journals Snow Level Characteristics and Impacts of a Spring Typhoon-originating Atmospheric River in the Sierra Nevada, USA

2018 ◽  
Author(s):  
Benjamin Hatchett
Keyword(s):  
Sierra Nevada ◽  
Debris Flows ◽  
Heavy Precipitation ◽  
Extratropical Cyclone ◽  
Snow Avalanches ◽  
Northeast Pacific ◽  
Atmospheric River ◽  
Super Typhoon ◽  
Wet Snow

On 5-7 April 2018 a landfalling atmospheric river resulted in widespread heavy precipitation in the Sierra Nevada of California and Nevada. Observed snow levels during this event were among the highest snow levels recorded since observations began in 2002 and exceeded 2.75 km for 31 hours in the northern Sierra Nevada and 3.75 km for 12 hours in the southern Sierra Nevada. The anomalously high snow levels and over 80 mm of precipitation caused flooding, debris flows, and wet snow avalanches in the upper elevations of the Sierra Nevada. The origin of this atmospheric river was super typhoon Jelawat, whose moisture remnants were entrained and maintained by an extratropical cyclone in the northeast Pacific. This event was notable due to its April occurrence, as six other typhoon remnants that caused heavy precipitation with high snow levels (mean = 2.92 km) in the northern Sierra Nevada all occurred during October.

scholarly journals Anisotropy of seasonal snow measured by polarimetric phase differences in radar time series

2015 ◽  
Vol 9 (6) ◽  
pp. 6061-6123 ◽  
Author(s):  
S. Leinss ◽  
H. Löwe ◽  
M. Proksch ◽  
J. Lemmetyinen ◽  
A. Wiesmann ◽  
...  
Keyword(s):  
Computer Tomography ◽  
Test Site ◽  
Snow Pack ◽  
Vertical Temperature ◽  
Structural Anisotropy ◽  
Radar Measurements ◽  
Natural Snow ◽  
The Town ◽  
Phase Differences

Abstract. Snow settles under the force of gravity and recrystallizes by vertical temperature gradients. Both effects are assumed to form oriented ice crystals which induce an anisotropy in mechanical, thermal, and dielectric properties of the snow pack. On microscopic scales, the anisotropy could be hitherto determined only from stereology or computer tomography of samples taken from snow pits. In this paper we present an alternative method and show how the anisotropy of a natural snow pack can be observed contact- and destruction-free with polarimetric radar measurements. The copolar phase differences (CPD) of polarized microwaves transmitted through dry snow were analyzed for four winter seasons (2009–2013) from the SnowScat Instrument, installed at a test site near the town of Sodankylä, Finnland. An electrodynamic model was established based on anisotropic optics and on Maxwell–Garnett-type mixing formulas to provide a link between the structural anisotropy and the measured CPD. The anisotropy values derived from the CPD were compared with in-situ anisotropy measurements obtained by computer tomography. In addition, we show that the CPD measurements obtained from SnowScat show the same temporal evolution as space-borne CPD measurements from the satellite TerraSAR-X. The presented dataset provides a valuable basis for the future development of snow models capable of including the anisotropic structure of snow.

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