INFLUENCE OF THE I95-INDEX AND LOCAL PARAMETERS ON THE ACCURACY OF GNSS POSITIONING

Abstract

Although originally developed for military purposes, Global Navigation Satellite Systems have become indispensable for an ever-growing range of civil and scientific applications such as cartography, cadastral and land information systems, transport systems, precision agriculture, self-driving vehicles, rescue missions, etc. The accuracy of positioning by means of GNSS, however, is affected by atmospheric distortions of the GNSS signals as well as by the characteristics of the receiver (e.g. number of channels, firmware, etc.), local external influences (e.g. reflective surfaces, obstructions, electromagnetic distortions, etc.), and the system used to correct these distortions (e.g. SBAS, RTK, RTK-network, post-processing, etc.). Hence, to predict the accuracy of the positioning, it is important to understand the degree of robustness of the system (receiver and method) in terms of the degree in which it is affected by ionospheric conditions and local external influences. For this research the system consisted of a Septentrio ALTUS NR3 GNSS receiver in combination with the Flemish RTK-network FLEPOS, Belgium. To assess the accuracy and its variations, measurements in varying external circumstances, were performed according to the of ISO 17123-8 standard during the period November 2021 - April 2022. The results show that the system is very robust for the influence of the I95 index and the location specific parameters: proximity of high voltage cables and windmills. However, the distance to the nearest reference station and the number of visible satellites can affect the precision. Further research is necessary to assess the influence of other parameters.