Abstract
In sport science, Global Navigation Satellite Systems (GNSS) are frequently applied to capture athletes' position, velocity and acceleration. Application of GNSS includes a large range of different GNSS technologies and methods. To date no study has comprehensively compared the different GNSS methods applied. Therefore, the aim of the current study was to investigate the effect of differential and non-differential solutions, different satellite systems and different GNSS signal frequencies on position accuracy. Twelve alpine ski racers were equipped with high-end GNSS devices while performing runs on a giant slalom course. The skiers' GNSS antenna positions were calculated in three satellite signal obstruction conditions using five different GNSS methods. The GNSS antenna positions were compared to a video-based photogrammetric reference system over one turn and against the most valid GNSS method over the entire run. Furthermore, the time for acquisitioning differential GNSS solutions was assessed for four differential methods. The only GNSS method that consistently yielded sub-decimetre position accuracy in typical alpine skiing conditions was a differential method using American (GPS) and Russian (GLONASS) satellite systems and the satellite signal frequencies L1 and L2. Under conditions of minimal satellite signal obstruction, valid results were also achieved when either the satellite system GLONASS or the frequency L2 was dropped from the best configuration. All other methods failed to fulfill the accuracy requirements needed to detect relevant differences in the kinematics of alpine skiers, even in conditions favorable for GNSS measurements. The methods with good positioning accuracy had also the shortest times to compute differential solutions. This paper highlights the importance to choose appropriate methods to meet the accuracy requirements for sport applications.
Highlights
The goal of this study is to investigate which
The antenna was mounted on the helmet and connected to a receiver, which was carried in a cushioned backpack
The current study produced the following main findings: (1) For the periods when solutions were computed the spatial differences were smallest for method A, followed by C, B, D and E; (2) The period of time for which no differential solution could be computed was shortest for method A and increased for methods B, C and D respectively; (3) Methods A, B and C were approximately accurate for the 10° condition; (4) Time to fix integer ambiguities was shortest for method A followed by methods C, B and D
Summary
Global Navigation Satellite Systems (GNSS) are frequently applied to capture athletes’position, velocity and acceleration (PVA) in team sports [1,2] and individual sports, such as running/locomotion [3,4,5,6,7,8,9,10,11,12,13,14,15], orienteering [16], sailing/rowing [17], ski jumping [18], cross country skiing [19,20,21], snowboarding [22,23], and alpine skiing [24,25,26,27,28,29,30,31]In the sport of competitive alpine skiing, there are three main demands on a valid and practicable measurement system for capturing skiers’ kinematics: (1) it has to fulfill high accuracy standards in order to detect the small but substantial differences between athletes’ trajectories [32,33]; (2) it should cause minimal interference with the athletes’ competitive skiing [34]; (3) it should allow the largest possible capture volumes in order to be able to analyze entire competitions and/or training runs.In order to meet these requirements, to date a number of different methods have been suggested: non-differential GNSS methods [31,35], real-time differential GNSS methods [25,36,37] and post-processed, differential GNSS methods [30,38]. In the sport of competitive alpine skiing, there are three main demands on a valid and practicable measurement system for capturing skiers’ kinematics: (1) it has to fulfill high accuracy standards in order to detect the small but substantial differences between athletes’ trajectories [32,33]; (2) it should cause minimal interference with the athletes’ competitive skiing [34]; (3) it should allow the largest possible capture volumes in order to be able to analyze entire competitions and/or training runs. Some differential methods use the L1 frequency only [28], while others use frequencies L1 and L2 [25,30]. Despite the large number of GNSS applications in alpine skiing and sports in general, no study has ever comprehensively compared the available GNSS methods with respect to position accuracy. The magnitude of position accuracy of the applied methods is largely unknown. Signal obstruction can lead to partial or total loss of satellite signals and loss of differential solutions
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