Research on three-dimensional position determination using GPS L1-C1 and Galileo E1-C1 observations

In recent years, parallel to the developments in satellite technology, it has become possible to determine low-cost, high-accuracy and real-time positioning with a single receiver, especially for navigational purposes. No GNSS reference station data is needed in this method, which is called single point positioning or absolute positioning, and point coordinates can be determined with high accuracy in both real-time and post-processing. Within the context of this thesis, a software named KTUN_HRT has been prepared for single point (absolute) positioning with code measurements. In this software, 3D point positioning accuracies have been investigated by Least Squares Method (LSM) using C1 code observations of GPS and Galileo satellite system, atmospheric correction models (ionosphere and troposphere), broadcast and precise ephemeris information. Also, a user-friendly interface has been designed and thus users have the opportunity to perform the computation scenarious depending on their preferences. In the numerical application part of the thesis, different computation scenarious were created using 24-hour observation data of 5 IGS stations on April, 22nd and 23rd 2021. The results obtained were compared with the results obtained using "Trimble CenterPoint RTX Post-Processing Service" and "AUSPOS", which are online GNSS data evaluation services. According to the aforementioned results, there is not much difference between Galileo and GPS solutions made using broadcast ephemerides, in other words, it remains within ± 1-3 meters accuracy limits. On the other hand, especially in the data dated April 22nd, Galileo+precise ephemeris solutions yielded more accurate results than GPS+precise ephemeris solutions. Besides, it was seen that the results obtained with RTX and AUSPOS, which are accepted as correct because they use multi-frequency and phase measurement data, are compatible with KTUN_HRT GPS results. As a result, it has been confirmed by RTX and AUSPOS solutions that the KTUN_HRT software, which was prepared within the context of this thesis study, can be used reliably for single point positioning applications.