Sosonka I. Analysis and quality estimation of coordinate time series of Ukrainian reference GNSS-stations

Long-term time series of GNSS-stations have been widely used to monitor Earth's movements (eg, plate tectonics, sea level changes, pole motion studies, etc.). We can detect a linear or nonlinear trend, annual and semi-annual signals, gaps, and measurement noise in the time series of coordinates. Most analysis methods are focused on identifying annual signals, analyzing time series gaps, and finally estimating reliable rates of reference station coordinates changes, as they must be stable for several decades, which requires reliable methods for observing and processing data and understanding basic dynamic processes. Depending on the nature of the signal and other factors that cause time series changes, specific methods are needed to distinguish between signals from tectonic movement and other non-tectonic signals, such as seasonal changes. These methods can be used both for visual interpretation and pre-processing of time series, and statistical analysis for their accuracy and the need to take into account a number of systematic errors sources. Visual interpretation and pre-processing of the obtained time series of coordinates includes detection and removal of offsets and random errors, noise characteristics, assessment of the trend and seasonal changes, as well as analysis of residual errors. Regarding statistical analysis on the need to take into account a number of systematic errors sources, it is possible to use a wide range of mathematical approaches. One of them is the Non-classical error theory of measurement (NETM). It is defined as a modern theory of mathematical processing of time series data with a sufficiently large sample size (more than 500) because it is known that with multiple GNSS-measurements, the fundamental principles of Classical error theory of measurement (CETM) cease to be representative. Thus, the main attention of this dissertation is focused on conducting research of time series for qualitative assessment of the accuracy of determining the coordinates and assessing the suitability of Ukrainian GNSS-stations for geodynamic researches.