This study examines the effect of baseline length on accuracy and precision in Network Real-Time Kinematic (NRTK) positioning and develops an experimental mathematical model to express this effect. The study also measures the performances of the Flaechen Korrektur Parameter (FKP) and Virtual Reference Stations (VRS) methods at different baseline lengths. The study makes use of the stations that form two Continuously Operating Reference Station (CORS) networks, one of which is local and the other national. Calculations were made to perform various geodetic operations, such as datum transformations between the two networks, identifications of positional velocities, and epoch shifting. BERNESE (v5.2) software was used to identify coordinate values assumed to be true based on International GNSS Service (IGS) products. No significant changes were observed in the RMSE values in baseline lengths of up to 40 km. In contrast, an average linear correlation of 69.2% was determined between precision and baseline length. Measurements were evaluated and tested using the variance model created as a function of the baseline length, in line with the aims of the study, and the results were found to be consistent. Moreover, in an examination of the Root Mean Square Error (RMSE) and precision values of the FKP and VRS measurements, no significant differences were observed. The mean differences were at the millimetre level.

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In this paper, to investigate the usability of Continuously Operating Reference Stations managed by the Istanbul Water and Sewerage Administration (ISKI CORS) for weather prediction studies, the effects of altitude and distance on Zenith Tropospheric Delay (ZTD) and Integrated Water Vapour (IWV) estimations were analysed. Within the scope of this study, the authors determined accuracies of ZTD and IWV values-based on the selected reference stations and analysed them for altitude and distance factors. GnSmart software is used for ZTD estimation as this software broadcasts CORS correction and GNSS Analysis and Positioning Software (GAPS) is used for IWV estimation. In this study, a single reference station was used to test the accuracy of ZTD and IWV values obtained from local ISKI CORS network stations (TUZL station for ZTD values and radiosonde station numbered 17064 for IWV values). The determined RMSE values could not reach the ZTD and IWV precision standards of the World Meteorology Organization (WMO). One reason for this is that a single station is selected as a reference. In short, the authors express that the ZTD and IWV values of ISKI CORS stations are not similar, but there is a significant difference between them. It was also understood that a single radiosonde station is not sufficient to determine the IWV values of the stations in the local ISKI CORS network, and the GNSS IWV values obtained from the stations can be meaningful.

The geometric design of the Continuously Operating Reference Station (CORS) network is one of the most critical factors that impact accuracy, precision, and Time to Fix Ambiguity (TTFA) performance. In this study, the authors investigate the subject of geometric design by using both local ISKI CORS and national CORS-Turkey (CORS-TR) networks, and they redesign the ISKI CORS network by increasing interstation distances. For three systems, real-time Virtual Reference Station (VRS) solutions have been obtained and tested with Analysis of Variance (ANOVA). As a result, the 8-station ISKI CORS provides the most accurate results in the vertical component. In contrast, for TTFA performance, the CORS-TR network shows worse outcomes than the others. Due to the increase in the interstation distances, the increase in the base length caused worse results in FIX solution ratios for redesigned ISKI CORS. In summary, the authors have stated that the 8-station ISKI CORS network performs better, especially regarding vertical accuracy. Furthermore, the authors state that the TTFA performance and FIX solution ratios are high, and the ISKI CORS geometric design is optimal.

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