ASSESSMENT OF ACCURACY OF RTK MEASUREMENTS USING VARIOUS COMBINATIONS OF GNSS

In the present paper attempt was done to examine the impact of the number of observed satellites, from various Global Navigation Satellite Systems (GNSS) on the results of measurements performed using RTK technique (Real Time Kinematic). The research was performed in static mode at four stations with the use of various combinations of four currently available systems: GPS, GLONASS, BDS and GALILEO. The coexistence of four different independent Global Navigation Satellite Systems gives the user wide possibilities of use Multi-GNSS applications if only the receiver of satellite signals has the technical capabilities. Using the Multi-GNSS increases the number of observed satellites, which results in the increase in the number of observed signals and frequencies. In turn, the increase in the number of observed signals and frequencies (observation) has a direct impact on the growth of availability and range of the used measurement method, it also gives a chance, that the results will be characterized by higher reliability and accuracy. However, for this to be possible, the user must be equipped with a dual-system receiver, and Multi-GNSS applications must properly take into account in solving inter alia, aspects such as, different reference systems, different time systems, different satellite orbits for each of the used systems. Only then measurements using satellites from various positioning and navigation systems will give better results in comparison to a situation when only one GPS system is used. In the work multiple, daily research measurements using multi-satellite receivers, Trimble R10 GNSS System, were made in four combinations: GPS, GPS+GLONASS, GPS+GLONASS+BDS, GPS+GLONASS+BDS+GALILEO. To compare the accuracy of position determination in various combinations, from the coordinates obtained from the measurements the coordinates of the reference checkpoint were subtracted. On this basis it has been shown empirically, that a greater number of observed satellites can significantly improve the accuracy and reliability of satellite measurements. It has been proven also, that it also affects the improvement of the observation conditions defined by DOP parameters (Dilution of Precision). The research has shown that the increase of the number of the observed satellites under certain conditions can lead to the reduction in errors of determined coordinates up to about 30%.