Validity and reliability of a radio positioning system for tracking athletes in indoor and outdoor team sports.

Radio-frequency local positioning systems (LPS) have the potential to provide accurate location information about sport players for performance analysis, making available for study the emergent nature of interpersonal coordination and collective decision-making behaviour among players in both indoor and outdoor sports. However, no available publications have validated the performance of LPS for indoor sports. The objective of this study was to validate the performance of an LPS in an indoor venue and to compare it to performance observed in an outdoor venue using static and dynamic measurements. Our results showed that the absolute positioning errors obtained from the static measurements of the LPS were comparable for both indoor and outdoor venues, with mean errors of 12.1 cm outdoors and 11.9 cm indoors. From the dynamic measurements, we analysed the relative position error and the distance estimation performance of the system. The 90th-percentile relative position errors were 28 cm for the indoor venue versus 18 cm for the outdoor venue. On average, the LPS overestimated the distance travelled, and the performance was similar for both indoor and outdoor venues. On a linear course, the mean errors of the distance estimates were 2.2% of the total distance indoors and 1.3% outdoors, and on a nonlinear course, they were 2.7% indoors and 3.2% outdoors.

Single- and double-difference algorithms for position and time-delay calibration of transducer-elements in a sparse array.

A method for the calibration of the position and time delay of transducer elements in a large, sparse array used for underwater, high-resolution, ultrasound imaging has been described in a previous work. This algorithm is based on the direct algorithm used in the global positioning system (GPS), but the wave propagation speed is treated as one of the to-be-calibrated parameters. In this article, the performance of two other commonly used GPS algorithms, namely the single-difference algorithm and the double-difference algorithm, is evaluated. The calibration of the propagation speed also is integrated into these two algorithms. Furthermore, a novel, least-squares method is proposed to calibrate the time delay associated with each transducer element for these two algorithms. The performances of these algorithms are theoretically analyzed and evaluated using numerical analysis and simulation study. The performance of the direct algorithm, the single-difference algorithm, and the double-difference algorithm is compared. It was found that the single-difference algorithm has the best performance among the three algorithms for the current application, and it is capable of calibrating the position and time delay of transducer elements to an accuracy of one-tenth of a wavelength.

Comparison of Organic Compound Compositions in the Emissions Inventory and Ambient Data for the Lower Fraser Valley.

Weimin Jiang (corresponding author) is a research associate at the Institute for Chemical Process and Environmental Technology, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6; phone: (613) 998-3992; e-mail: weimin.jiang@nrc.ca. Don Singleton and Mark Hedley are research officers at the Institute for Chemical Process and Environmental Technology, National Research Council, Canada. Non-methane organic compound (NMOC) composition in an episode-specific emissions inventory is systematically compared with the average summer ambient NMOC composition in the Lower Fraser Valley (LFV) of British Columbia, Canada. The comparison is made on the basis of NMOC classes, carbon numbers of species and classes, and individual chemical species. The composition of species present in the inventory but not measured in the atmosphere is also presented. It is found that the ambient and emissions inventory compositions are in reasonable agreement, with a few exceptions. Because of the similarity in the compositions, the emissions profile in the LFV can be used to approximate the ambient NMOC profile in photochemical modeling of the region. A similar validation procedure would be required in other regions.Discrepancies exist between the emissions inventory and the ambient data for the biogenic compounds isoprene.