The importance of reference stations geometry and distance to rover in GNSS Network-RTK system

Global Navigation Satellite Systems (GNSS) have taken their place in our daily lives by providing fast, economical and reliable positioning services. Network RTK, which is one of the GNSS positioning methods, provides real-time, high quality, efficient and powerful results. The distance dependent errors introduced by the classical RTK technique have been largely eliminated with the Network-RTK technique, and the determination of the 3D real-time coordinates of the rover receivers with an accuracy of 2-6 cm in the Network-RTK technique has become a standard practice today. These accuracies are achieved by interpolating the atmospheric parameters obtained from the Network RTK reference stations located approximately 40–80 km around the rover receiver point, as in the example of the TUSAGA-Aktif (Türkiye) network. As a result, the standard deviations of the calculated rover coordinates are highly dependent on the geometry of the Network-RTK reference stations and the distance between the rover receiver and the reference stations. Therefore, the accuracy of a rover coordinate within, for example, 10 km from the reference station will be different from the accuracy of a rover coordinate within, for example, 150 km from the reference station, depending on these parameters. In order to determine these distance dependent accuracies, some criteria are needed. The concept of IDOP (Interpolative Dilution Of Precision) as a unitless quantity can be used. On the other hand, the accuracy of the rover coordinates in network RTK measurements also depends on the geometry of the surrounding reference stations (used to calculate the rover coordinates). The IDOP concept is used in the OPUS-RS network-RTK software in the USA, and it is evaluated that there is not enough work on reference station geometry and IDOP concept in Türkiye. For the above mentioned reasons, this thesis will investigate the effect of both the geometry of the reference stations and the IDOP concept on the real-time determination of the rover receiver coordinates via TUSAGA-Aktif.