Construction of large hydropower complex is accompanied by a signifi cant technological impact on the environment. Large volumes of soil are redistributed, groundwater regime varies, there is the risk of deformation of the earth surface. One of the main methods of monitoring this dangerous phenomenon is the application of GNSS technology. The implementation of this method without a loss of coordinate accuracy depends on the conditions of horizon openness on the point of observations and the absence of objects causing multibeam eff ect, what is not always possible. This condition is not implemented on all points. Conducting high accuracy linear and angular observations in a complex with GNSS measurements will allow provide the necessary accuracy for the determination of the coordinates and their displacements. Main Research of the Problem

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The main directions and results of the activity of the famous talented scientist and teacher of the Lviv Geodetic School, professor A.L. Ostrovsky. On January 19, 2023, the Lviv geodetic community honored the 100th anniversary of the birth of Ostrovsky Apollinariy Lvovich – an outstanding scientist, professor, teacher known in Ukraine and abroad. Professor A. L. Ostrovsky published more than 200 scientific works, dozens of methodical developments in geodesy, topography; instrument science, he owns 11 copyright certificates and inventions. The birth of the Lviv School of Refraction is connected with the then professors of the Lviv Polytechnic Institute A. D. Motornyy and M. K. Mygal, and the first studies of the influence of atmospheric refraction on geodetic measurements were initiated by A. L. Ostrovsky To a large extent, the success in this work was brought about by the scientific activity of the employees of the branch research laboratory, which was managed by Apollinariy Lvovych in 1979–2006. This is how the Lviv Geodetic School of Refraction, known in the scientific world, was created. For many years, Prof. A. L. Ostrovsky headed the regional specialized Council for the defense of doctoral theses in geodesy, actively worked in the Educational and Methodological Council of the Ministry of Education and Culture of Ukraine, in the editorial boards of all scientific journals on geodesy and engineering geodesy published in Ukraine, and was the first editor-in-chief of the scientific journal Geodynamics. He was the scientific supervisor of almost 30 applicants who worked on candidate and doctoral theses. Among the pupils and students of Prof. A. L. Ostrovsky was an academician of the National Academy of Sciences of Ukraine Ya.S. Yatskiv, more than ten leading geodesist professors, many heads of geodetic enterprises and institutions in Ukraine and abroad. The fruitful scientific, pedagogical and professional activity of Prof. A. L. Ostrovsky brought him well-deserved respect in the scientific world and geodetic production, and was awarded high titles – Honored Worker of Science and Technology of Ukraine, “Honorary Surveyor of the USSR”, “Honorary Surveyor of Ukraine”, awarded with the Order of Merit III degree, and many honorary awards and medals. Professor A. L. Ostrovsky was a scholarship recipient of the President of Ukraine. Evidence of the unparalleled authority and deep respect on the part of the scientific geodetic community for A.L. Ostrovsky is the fact that he was elected as the head and honorary chairman of the organizing committee of the International Scientific and Technical Symposium “Geodetic Environmental Monitoring: GPS and GIS Technologies”, which has been held annually for many years worked in Alushta (Crimea).