scholarly journals The Snow-Friction of Freestyle Skis and Snowboards Predicted From Snow Physical Quantities

2021 ◽  
Vol 7 ◽  
Author(s):  
Fabian Wolfsperger ◽  
Frédéric Meyer ◽  
Matthias Gilgien
Keyword(s):  
Coefficient Of Friction ◽  
Global Navigation Satellite Systems ◽  
Multivariate Statistical ◽  
Severe Injuries ◽  
Satellite Systems ◽  
Wide Range ◽  
The Coefficient Of Friction ◽  
Snow Conditions ◽  
Global Navigation Satellite ◽  
Physical Quantities

Previous research has shown that friction between ski and snow can vary substantially due to changes in snow conditions. The variation of friction affects the speed a freestyle skier or snowboarder (athlete) reaches during the in-run of a jump. Athletes risk severe injuries if their take-off speed is not within the right margin to land in the “sweet spot” zone. To reduce the risk of injury, snow park designers and competition managers need to calculate the speed athletes reach during the in-run. However, despite multiple attempts over the last decades, to date no model can predict ski-snow friction from snow physical quantities. Hence, simulations of in-run speeds suffer from insufficient validity. For the first time, this work combines kinematic athlete data and comprehensive snow surface measurements to infer the coefficient of friction of freestyle skis and snowboards across a wide range of snow conditions. Athletes’ point mass kinematics were recorded at more than 200 straight gliding runs with differential global navigation satellite systems. The subjects’ air drag and lift were deployed from wind tunnel measurements. Along with the kinematic data and data from wind measurements, a mechanical model of the athlete was established to solve the equation of motion for the coefficient of friction between ski/snowboard and snow. The friction coefficients for ski (snowboard) ranged from 0.023 ± 0.006 (0.026 ± 0.008) to 0.139 ± 0.018 (0.143 ± 0.017) and could be explained well (Radj2 = 0.77) from the measured snow parameters using a multivariate statistical model. Our results provide a new quantitative tool for practitioners to predict the friction of skis and snowboard on snow of various conditions, which aims to increase athletes’ safety in slopestyle and big air.

scholarly journals GNSS Interference Environment in Malaysia: A Case Study

2021 ◽  
Vol 3 (1) ◽  
pp. 13-16
Author(s):  
Ooi Wei Han ◽  
Shahrizal Ide Moslin ◽  
Wan Aminullah
Keyword(s):  
Public Awareness ◽  
Essential Element ◽  
Global Navigation Satellite Systems ◽  
Space Technology ◽  
Local Study ◽  
Satellite Systems ◽  
Wide Range ◽  
Global Navigation Satellite ◽  
Significant Interference

Global Navigation Satellite Systems or GNSS is a space technology that has become an essential element nowadays for positioning, navigation & timing (PNT) with wide range of applications in many civilian sectors as well as across military. The reliability, accuracy and availability of GNSS are highly important especially for critical and precise positioning applications. However, the signals from space are weak and it can be easily blocked, disrupted or compromised by several other threats including intentional and unintentional interferences or jamming. GPS jammer is widely available off the shelf with an affordable price and capable of interfering the GPS signal, and many authorities worldwide have raised concerns and a lot of efforts and research have been put in place to reduce and mitigate the threats. In Malaysia, understanding and countering threats to GNSS/GPS based applications will be a new and unfamiliar discipline for public and organizations. This study intended to provide an overview of the GNSS interferences environment in a local study area, in terms of interference type and the number of activity pattern that were detected. A system called Detector V1 has been used in this study. The result showed that significant interference cases happened in the study area and some of the high power interferences may impact GNSS tracking and precision of the positioning output. The role objective of having this done is to create a public awareness regarding the threat of GNSS interferences to the local users. The content also includes the proposed initiative to overcome the issue.

scholarly journals Timing and Navigation in UAVs

2018 ◽  
Vol 5 (1) ◽  
pp. 17-25
Author(s):  
Karen Von Hünerbein ◽  
Werner R Lange
Keyword(s):  
Time Synchronization ◽  
Health And Safety ◽  
Test Methods ◽  
Global Navigation Satellite Systems ◽  
External Control ◽  
Satellite Systems ◽  
Environment And Health ◽  
Wide Range ◽  
Correct Function ◽  
Global Navigation Satellite

Precise timing and precise location information are provided by Global Navigation Satellite Systems (GNSS) and play a crucial role in the positioning, navigation and data acquisition of most Unmanned Aerial Vehicles (UAV). GNSS functions include the following applications in UAVs: time-stamping and geo-referencing of collected data and images, synchronization of swarm flying and follow-me flights, determination of position and attitude in-flight, flight trajectory by following a pre-defined number of waypoints, mission planning, return home automatically without external control, avoidance of obstacles and geo-fencing.  Some of these critical operations have implications for the safety of the UAV, the surrounding environment and health and safety of people, for example UAVs threatening to bring down aircrafts  at airports, which are no-fly zones for UAVs. The appropriate GNSS based function to avoid this is geo-fencing. Another example is obstacle avoidance to prevent collisions and damages both for the UAV and the obstacle, e.g. anything from a window pane, tree, human being, to a power line. In order to ensure health and safety it is thus important to ensure correct function of the navigation and the timing, under a wide variety of circumstances, and in different signal environments. There can be signal disturbances, such as obscurations by buildings or reflected GNSS signals, called multipath. The performance of timing and navigation based on GPS/GNSS can be tested and verified in a controlled and repeatable way in the laboratory with different types of test equipment. We will give an introduction to a wide range of potential threats to GNSS Positioning, navigation and timing and an overview of different test methods. In addition, we are presenting a method for time synchronization of drones to enable safe swarm and follow flights in UAVs.

Receiver Interface Requirements for Deep INS/GNSS Integration and Vector Tracking

2010 ◽  
Vol 63 (3) ◽  
pp. 471-489 ◽  
Author(s):  
Paul D Groves ◽  
Christopher J Mather
Keyword(s):  
Inertial Navigation System ◽  
Global Navigation Satellite Systems ◽  
Signal To Noise ◽  
Satellite Systems ◽  
Gnss Receiver ◽  
Wide Range ◽  
Vector Tracking ◽  
Update Rate ◽  
Global Navigation Satellite ◽  
Data Latency

Vector tracking of global navigation satellite systems (GNSS) signals and deeply integrating GNSS with an inertial navigation system (INS) improve robustness and accuracy in poor GNSS signal-to-noise environments. Both require a dedicated interface between the GNSS receiver and the navigation processor to enable the GNSS receiver to output the correlator measurements and input numerically-controlled oscillator (NCO) commands. This paper investigates the requirements for such an interface. Data latency is analysed for a range of different stand-alone GNSS vector tracking and deep INS/GNSS integration architectures. Suitable latency compensation techniques are identified. It is shown that, for the majority of applications, an NCO command update rate of 50 Hz with latency compensation and 100 Hz without is sufficient. An approach to interface standardisation which can handle a wide range of different GNSS signals and receiver designs is proposed.

Interference and Spoofing

2014 ◽  
pp. 54-83
Author(s):  
Fabio Dovis ◽  
Luciano Musumeci ◽  
Nicola Linty ◽  
Marco Pini
Keyword(s):  
Global Navigation Satellite Systems ◽  
Added Value ◽  
Positioning System ◽  
Navigation Satellite ◽  
Satellite Systems ◽  
Wide Range ◽  
Global Positioning ◽  
Military Applications ◽  
Processing Algorithms ◽  
Global Navigation Satellite

This chapter deals with one of the major concerns for reliable use of Global Navigation Satellite Systems (GNSS), providing a description of intentional and unintentional threats, such as interference, jamming, and spoofing. Despite the fact that these phenomena have been studied since the early stages of Global Positioning System (GPS), they were mainly addressed for military applications of GNSS. However, a wide range of recent civil applications related to user safety or featuring financial implications would be deeply affected by interfering or spoofing signals intentionally created. For such a reason, added value processing algorithms are being studied and designed in order to embed in the receiver an interference reporting capability so that they can monitor and possibly mitigate interference events.

scholarly journals Analytical Computation of the Spatial Resolution in GNSS-R and Experimental Validation at L1 and L5

2020 ◽  
Vol 12 (23) ◽  
pp. 3910
Author(s):  
Adriano Camps ◽  
Joan Francesc Munoz-Martin
Keyword(s):  
Spatial Resolution ◽  
Water Reservoir ◽  
Coherent Scattering ◽  
Step Function ◽  
Global Navigation Satellite Systems ◽  
Step Response ◽  
Satellite Systems ◽  
Remote Sensing Technique ◽  
Wide Range ◽  
Global Navigation Satellite

Global navigation satellite systems reflectometry (GNSS-R) is a relatively novel remote sensing technique, but it can be understood as a multi-static radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas, and even under dense vegetation show a detectable coherent component that can be separated from the incoherent component and processed accordingly. This work derives an analytical formulation of the response of a GNSS-R instrument to a step function in the reflectivity using well-known principles of electromagnetic theory. The evaluation of the spatial resolution then requires a numerical evaluation of the proposed equations, as the width of the transition depends on the reflectivity values of two regions. However, it is found that results are fairly constant over a wide range of reflectivities, and they only vary faster for very high or very low reflectivity gradients. The predicted step response is then satisfactorily compared to airborne experimental results at L1 (1575.42 MHz) and L5 (1176.45 MHz) bands, acquired over a water reservoir south of Melbourne, in terms of width and ringing, and several examples are provided when the transition occurs from land to a rough ocean surface, where the coherent scattering component is no longer dominant.

scholarly journals Slow deformation event between large intraslab earthquakes at the Tonga Trench

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yuta Mitsui ◽  
Hinako Muramatsu ◽  
Yusaku Tanaka
Keyword(s):  
Subduction Zone ◽  
Global Navigation Satellite Systems ◽  
Benioff Zone ◽  
Plate Interface ◽  
Satellite Systems ◽  
Deep Earthquakes ◽  
Wide Range ◽  
Slip Event ◽  
Deformation Event ◽  
Global Navigation Satellite

AbstractSlow deformations associated with a subducting slab can affect quasi-static displacements and seismicity over a wide range of depths. Here, we analyse the seismotectonic activities in the Tonga subduction zone, which is the world’s most active area with regard to deep earthquakes. In our study, we combine data from global navigation satellite systems with an earthquake catalogue. We focus on the deep earthquakes that are below 400 km at the lower part of the Wadati–Benioff zone. We find that trenchward transient displacements and quiescence of deep earthquakes, in terms of background seismicity, were bounded in time by large intraslab earthquakes in 2009 and 2013. This “slow deformation event” between 2009 and 2013 may have been triggered by a distant and shallow M8.1 earthquake, which implies a slow slip event at the plate interface or a temporal acceleration of the subduction of the Pacific Plate. These findings provide new insights into the relationship between shallow and deep earthquakes in the subduction zone.

Recent Trends in Interference Mitigation and Spoofing Detection

2012 ◽  
Vol 3 (3) ◽  
pp. 1-17 ◽  
Author(s):  
Fabio Dovis ◽  
Luciano Musumeci ◽  
Nicola Linty ◽  
Marco Pini
Keyword(s):  
Interference Mitigation ◽  
Global Navigation Satellite Systems ◽  
Added Value ◽  
Satellite Systems ◽  
Wide Range ◽  
Global Positioning ◽  
Military Applications ◽  
Recent Trends ◽  
Global Navigation Satellite

This paper gives a classification of intentional and unintentional threats, such as interference, jamming and spoofing, and discusses some of the recent trends concerning techniques for their detection and mitigation. Despite the fact that these phenomena have been studied since the early stages of Global Positioning System (GPS), they were mainly addressed for military applications of Global Navigation Satellite Systems (GNSS). However, a wide range of recent civil applications related to user’s safety or featuring financial implications would be deeply affected by interfering or spoofing signals intentionally created. For such a reason, added value processing algorithms are being studied and designed, in order to improve accuracy and robustness of the receiver and to assure the reliability of the estimated position and time solution.

scholarly journals Relative Positioning in Remote Areas Using a GNSS Dual Frequency Smartphone

Sensors ◽  
2021 ◽  
Vol 21 (24) ◽  
pp. 8354
Author(s):  
Américo Magalhães ◽  
Luísa Bastos ◽  
Dalmiro Maia ◽  
José Alberto Gonçalves
Keyword(s):  
Low Cost ◽  
Global Navigation Satellite Systems ◽  
Reference Station ◽  
Dual Frequency ◽  
Phase Measurements ◽  
Satellite Systems ◽  
Remote Areas ◽  
Wide Range ◽  
Innovative Capabilities ◽  
Global Navigation Satellite

The use of GPS positioning and navigation capabilities in mobile phones is present in our daily lives for more than a decade, but never with the centimeter level of precision that can actually be reached with several of the most recent smartphones. The introduction of the new GNSS systems (Global Navigation Satellite Systems), the European system Galileo, is opening new horizons in a wide range of areas that rely on precise georeferencing, namely the mass market smartphones apps. The constant growth of this market has brought new devices with innovative capabilities in hardware and software. The introduction of the Android 7 by Google, allowing access to the GNSS raw code and phase measurements, and the arrival of the new chip from Broadcom BCM47755 providing dual frequency in some smartphones came to revolutionize the positioning performance of these devices as never seen before. The Xiaomi Mi8 was the first smartphone to combine those features, and it is the device used in this work. It is well known that it is possible to obtain centimeter accuracy with this kind of device in relative static positioning mode with distances to a reference station up to a few tens of kilometers, which we also confirm in this paper. However, the main purpose of this work is to show that we can also get good positioning accuracy using long baselines. We used the ability of the Xiaomi Mi8 to get dual frequency code and phase raw measurements from the Galileo and GPS systems, to do relative static positioning in post-processing mode using wide baselines, of more than 100 km, to perform precise surveys. The results obtained were quite interesting with RMSE below 30 cm, showing that this type of smartphone can be easily used as a low-cost device, for georeferencing and mapping applications. This can be quite useful in remote areas where the CORS networks are not dense or even not available.

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