The paper studies the relationship between the ambient temperature change and the horizontal displacements on control points of the Dnieper Hydroelectric Station dam from 2016 to 2020. A specially developed software product analyzed the GNSS time series of measurements pre-processed by the GeoMoS system to determine the parameters of seasonal displacements and their relationship with seasonal changes in air temperature. The research established that the influence of ambient temperature in the absence of significant changes in the water level in the upper reservoir determines the cyclicity of dam deformations. It is established that the projections of velocity vectors of reference points in the ETRF-2014 system for the studied period do not exceed the absolute value of 3 mm/month. The directions of the horizontal displacement vectors in the first half of each year are opposite to the directions recorded in the second half. In the first half of the year, the dam’s body shifts towards the reservoir, while in the second half year period, it shifts-backwards. According to the three-year GNSS monitoring of the Dnieper Hydroelectric Station dam, the amplitude of semi-annual horizontal oscillations of the control points relative to the dam axis is from -9.5 to +8 mm. In winter and summer, the horizontal displacements increase from the edges of the dam to its central part, and the amplitudes of the horizontal displacements move vice versa. The obtained data establish a linear analytical relationship between the average temperature and the horizontal displacements of the GNSS control points.

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The aim of this work is to study the zenith tropospheric delay components fluctuations according to the atmospheric sounding data and analytical model in selected period and accuracy assessment of Saastamoinen model. Methodology. The main methods for calculation ZTD are atmospheric sounding and using analytical models. To study ZTD components we use atmospheric sounding data conducted at 4 Ukrainian upper air stations (Kyiv, Kharkiv, Lviv, Odesa) with 24 hours frequency, as well as near-surface atmospheric variables provided by weather stations with 3 hours frequency in the period from January 1 to December 31, 2019. ZTD components were calculated by integration using sounding data, and using Saastamoinen’s formulas. Based on the calculated data, created graphs comparing the values of sounding and model. Calculated the standard error of Saastamoinen model. Results. Compared ZTD components at points, located in different climatic zones, using the atmospheric pressure reduced to sea level. Both ZDD and ZWD are the largest at Odesa station. Annual fluctuation of ZDD are 8–20 mm and ZWD fluctuations are 75–95 mm. The daily amplitudes of ZDD are 5–6 mm in summer and 12–13 mm in winter. The daily amplitudes of ZWD are 20–30 mm in summer and 6–8 mm in winter. The standard error of Saastamoinen’s model is 7 mm for ZDD and 22 mm for ZWD. Scientific novelty and practical significance in that the study can improve accuracy and evaluate the feasibility of using different methods for calculating ZTD, see the dynamic of change ZDD and ZWD and their behavior over a long period. The results can be used for further studies of ZTD and improving the accuracy of satellite observations.

The aim of this work is to study the fluctuations of the components of the zenith tropospheric delay during the annual period according to the ground meteorological measurements in Ukraine. Methodolodgy. The surface values of meteorological values at the stations: Lviv, Kyiv, Kharkiv and Odesa, obtained in 2019 with an interval of 3 hours were used for the research. A total amount of 2020 measurements at each of the stations has been presented. The calculation of the components of the zenith tropospheric delay was performed according to the Saastamoinen formula. According to the calculated values of the components, graphs of changes in the dry and wet components of the zenith tropospheric delay for each of the stations during constructed. Subsequently, the monthly average and annual average values of the components were calculated and compared with each other. Results. Based on studies of changes in delay values at four Ukrainian meteorological stations for the period of 2019, it was found that the monthly average values of ZHD component are higher at stations whose altitude is lower. The wet component of ZWD during the year acquires the biggest values in summer. Annual fluctuations of the dry component of ZHD have a much smaller amplitude than the wet ZWD. The amplitude of the change in the total delay is determined by the amplitude of the change of the wet component, which at different stations is almost two times bigger than the amplitude of the change of the dry component, although ZWD is only up to 10% of ZTD. Thus, the variations in the total tropospheric delay, which indirectly reflects the weather and climatic processes due to variations in the wet component. Scientific novelty and practical significance consist in identifying the features of the annual change in the components of tropospheric delay at stations in different climatic and weather conditions. The performed research can be used in the tasks of monitoring of large hydraulic structures by GNSS methods to create regional models of the atmosphere and further studies of tropospheric delay, as they relate to its changes in space and time.

The aim of this work is to evaluate the accuracy of determining the wet component of zenith tropospheric delay (ZTD) from GNSS-measurements and the accuracy of determining the hydrostatic component according to the Saastamoinen model in comparison with the radio sounding data as well. Zenith tropospheric delay is determined mainly by two methods - traditional, using radio sounding or using atmospheric models, such as the Saastamoinen model, and the method of GNSS measurements. Determination of the hydrostatic component of the zenith tropospheric delay was performed by radio sounding data obtained at the aerological station Praha-Libus in 2011-2013 and in 2018. Data were processed for the middle decades of January and July of each year at 0h o’clock of the Universal Time. The wet component was calculated from GNSS observations. By a significant number of radio soundings at the Praha-Libus aerological station, hydrostatic and wet components of zenith tropospheric delay (ZTD) and the same number of ZTD values derived for the corresponding time intervals from GNSS measurements at the GOPE reference station were determined. The values of the wet component of ZTD were determined and compared with the corresponding data obtained from radio soundings. We found that the error of the hydrostatic component in winter does not exceed 10 mm in absolute value, and in summer it is approximately 1.5 times smaller. This is due to differences in the stratification of the troposphere and lower stratosphere in winter and summer. As for the wet component of ZTD, its errors do not exceed: in winter 15 mm, in summer – 35 mm. The resulting differences in summer have a negative sign, indicating a systematic shift, and in winter – both negative and positive. Today, there are many studies aimed at improving the accuracy of determining zenith tropospheric delay by both Ukrainian and foreign authors, but the problem of the accuracy of the hydrostatic component remains open. The study provides recommendations for further research to improve the accuracy of zenith tropospheric delay.