Snow sports & applications ¶

This study investigates how landing stability on slopestyle jumps is affected by jump design and the athletes' aerial maneuvers, in World Cup skiers and snowboarders. The data were recorded on rollover jumps from a World Cup Slopestyle competition using a geodetic video method, allowing for a reconstruction of the athletes' center of mass trajectories in 3D-space and calculation of equivalent fall height (EFH). Aerial maneuvers and landing stability were assessed by human raters. A generalized estimating equations method with binary logistic regression was performed to investigate how aerial maneuvers and EFH impact landing stability (surrogate measure of potential injury risk). EFH increased the log odds for unstable landings for both skiers and snowboarders. Although five aerial maneuver factors affected landing stability for snowboarders (angular velocity, rotational axis, number of rotations, with interaction effects between multiaxial maneuvers and frontside rotation or switch landing), skiers landing stability was only affected by the number of rotations. This, along with the way skiers and snowboarders are attached to their equipment and their ability to compensate for instability in the landing, may explain why snowboarders show unstable landings more often than skiers. On this study's rollover jumps with generally low EFH, landing stability was regulated by both EFH and aerial maneuvers. As maneuver complexity and EFH have an influence on both performance and landing stability, it appears important that course builders emphasize the construction of safe jumps and athletes generate a good understanding of potential injury risk and performance reward when jumping.

Glide-snow avalanches are a growing problem in alpine regions, driven by a warming climate
exacerbating extreme snow fall events and rapid warming periods. Glide-snow avalanches are problematic
given their unpredictability. Glide-snow cracks open in the snowpack presenting a threat to transport routes
and ski areas. The time of glide-snow avalanche release can be hours, days or weeks after crack opening.
With growing understanding of the mechanisms driving the formation and release of glide-snow avalanches,
it has been identified that interfacial water accumulation at the snow-ground boundary can reduce bonding
friction and drive glide-snow activity.

Wieviel Schnee aus 1 m³ Wasser entsteht ist bei der Beschneiung eine entscheidende Größe. Die Annahme eines realistischen Wertes dieses sogenannten Wasser-Schnee Faktors ist wichtig, um die Produktivität eines Schneeerzeugers sowie den Energieverbrauch (kWh) pro Kubikmeter Schnee korrekt zu bestimmen. Das SLF in Davos führte zu diesen Kennzahlen Studien durch, die bezüglich Planung von Beschneiungsanlagen zu verblüffenden Ergebnissen führen.

Quantifying the density (ρ) and liquid water content (LWC) of snow is crucial for any physical process in the snowpack. A widely used method to measure those quantities involves a ca-pacitance sensor that subjects the snow to an electrical field, an idea first introduced by Denoth (1989). While this dielectric measurement principle is known to be well-working from yearlong use of Denoth prototype sensors, such instruments are not yet commercially available. To this end, we developed a new ρ and LWC sensor with the goal of producing a small batch series in the near future. The sensor is a single coplanar capacitor integrated onto a printed circuit board that measures the relative permit-tivity (ε) of snow. We evaluated the sensor in the field through 13 dry and wet snow profiles and com-pared ε-values obtained from the new sensor with those measured with a Denoth prototype. An addi-tional validation was carried out in the cold lab on homogenous dry and wet snow samples. Field meas-urements deviated on average by 9.7 % (RMSE) and lab measurements by 2.9 % (RMSE) from the reference values. A comparison of the snow density, retrieved from ε using the Denoth inversion, with densities from volume weighing revealed an average deviation of 62 kg m-3 (19.7 %). The new sensor provides a reliable instrument to replace the established, but no longer available Denoth sensors. The accuracy of the new (and likewise the old) sensor may be improved if a better inversion model was available. A thorough understanding of the uncertainties in the dielectric calibration and uncertainties of the empirical permittivity parameterization relating ε, ρ and LWC may therefore lead to improved estimates in the future using the same device.

Objectives: Design parameters and landing impacts for selected snow park jumps in Switzerland were compared with the parameters recommended to increase the jumps’ safety by the Swiss Council for Accident Prevention (BFU). High impact zones were identified to help snow park shapers optimize the design of their jumps. A rough estimate of the influence of snow hardness on landing impacts was also provided.
Design: During the 2020/2021 winter season three-dimensional geometries of 23 jumps were captured using differential global navigation satellite system and terrestrial laser scanning. A point mass model was used to numerically calculate trajectories. The equivalent fall height (eFH) was used to quantify landing impacts and an empiric snow-deformation function was applied to take the effect of snow hardness into consideration. Workshops were held to discuss results and transfer findings.
Methods: 2D-profiles of the jumps were estimated by projecting the captured 3D position data onto the longitudinal cross-section plane. Table and landing geometry were smoothed and interpolated to a spatial resolution of 0.1 ​m, while the kicker was fitted with a 2nd order polynomial. Trajectories were numerically calculated for take-off speeds from 6 to 17.6 ​m ​s⁻¹ including aerodynamic forces using the Runge-Kutta method. The calculated eFH at the landing points were used to divide the landing into low-impact, medium-impact, and high-impact zones.
Results: Medium sized jumps had a low-impact zone of sufficient length (>6 ​m) and eFH smaller than 1.5 ​m throughout the entire table meeting the BFU recommendations. Nevertheless, critical eFH larger than 1.5 ​m, were obtained when take-off speeds increased by only 1.14 ​m ​s⁻¹. Large jumps had low-impact zone lengths in accord with the recommendations (>9 ​m), but high eFH (2.3–3.4 ​m) occurred for table landings. 10 of the 13 XL-jumps had long low-impact zones of approximately 12–15 ​m. Besides the risk of high impact landings towards the end of the landing area, as found similarly for the smaller jumps, portions of XL-jumps had very high eFH (2.6–4.6 ​m) for table landings.
Conclusions: The study confirmed the existing BFU recommendations of size categories, design parameters and landing impacts limits as prevalent and practicable and provided knowledge for future safety recommendations. Modifying table geometries and taking measures to limit the in-run speeds would help reduce landing impacts, and the hazard due to hard snow conditions should also be considered.