Research on tropospheric effect calculation models in GNSS positioning

Global Navigation Satellite System (GNSS) is the highest accuracy positioning and navigation system ever developed. However, as in every system, GNSS also has some weaknesses. In other words, there are some random errors and biases (systematic effects) that affect the results obtained with GNSS. Although these errors do not cause a significant problem in some GNSS applications, it should be modeled very well, especially in scientific studies that require high accuracy. These biases and errors may be cassified as those originating at the satellites and at the receiver systems and those caused by the measurement environment (signal propagation, multipath, etc.). One of these signal propagation errors is the tropospheric delay effect. This effect cannot be eliminated by using multi-frequency receivers as in the case of the ionospheric delay effect, but it can be eliminated with some algorithms and models. Especially in recent years, tropospheric model algorithms have been developed that provide solutions at elevation angles of 10 degrees and less. Within the scope of this thesis, tropospheric models which are being widely used in GNSS processing softwares, were examined and the mathematical algorithms of these models were adapted on the MATLAB (R2020a) platform. With the written software, a user-friendly interface has been designed, and users are provided with the opportunity to make any calculations they wish with a large number of calculation scenarios. In the numerical application part of the thesis, data sets of 17 TUSAGA-Aktif (CORS-TR) stations dated February 10, 2020 were used. According to the results obtained, it was determined that the Niell and VMF models gave the most appropriate results in scientific studies that require high accuracy, while the use of traditional Saastamoinen and Hopfield models is sufficient for applications that do not require high accuracy (e.g. for military, navigation and positioning purposes with single frequency receivers).