Goal. The development of conceptual frameworks and proposals to optimize the geometry of Dnister PSPP control GNSS network and to identify ways to improve the accuracy of GNSS measurements. Methodology. To select optimal geometric deployment of new and to clarify the position of existing points of Dnister PSPP control GNSS network it was developed a special methodology of optimizing the geometric configuration of the network. It foresees detecting of points position at which the value of optimization criteria will be minimal. As optimization criterion it was used the determinant of covariance matrix. Results. A methodology for optimizing the geometric network configuration using mathematical modeling was devised. As a result of the in-field inspection of points as well as detailed analysis conducted and processed measurements there were highlighted three key challenging groups of points of Dnister PSPP control GNSS network: points with poor reception of satellite signal; points centered using a tripod; points damaged during construction works. In order to improve rigidity and accuracy of Dnister PSPP control GNSS network it is necessary: to exclude the application of 4 GNSS measuring points (Portal-2, Nyzhniy, OZS-1-1 and OZS-23-2); to strengthen 4 points (GZ-10, GZ-11A, GZ-11B and GZ-12) with joint satellite angular and linear measurements; to replace 4 existing points (PP-221, PP-100, Obryv and OGZ-1) and set new 4 points

(GZ-21, GZ-22, GZ-23 and GZ-24). To install the new points four areas were determined and they need monitoring. Optimization of Dnister PSPP control GNSS network using the devised methodology resulted in improved accuracy (by 8.3-10.0 %) depending on the amount of used GNSS receivers. Scientific novelty and practical significance. A new methodology of optimizing the geometric network configuration using mathematical modeling is proposed. Using this methodology Dnister PSPP control GNSS network was optimized. The methodology can also be applied to optimize other geodetic monitoring networks.

- 1. Bisovetskiy Yu., Tretyak K., Shchuchik E. Avtomatizatsiya geodezicheskikh nablyudeniy za gidro-tekhnicheskimi sooruzheniyami gidroelektrostantsiy Ukrgidroenergo [Automation of geodetic observations of hydraulic structures of "Ukrhydroenergo" hydroelectric power stations], Gіdroenergetika Ukraїni [Hydropower of Ukraine], 2011, no. 2, pp. 45–51.

2. Galaganov O., Guseva T., Labuntsova L. Geodina¬mіchniy monіtoring іz zastosuvannyam suputnikovikh tekhnologіy deyakikh rayonіv AYES [Geodynamic monitoring using satellite technology some nuclear areas], Zbіrnik materіalіv IKh-go mіzhnarodnogo naukovo-tekhnіchnogo simpozіumu "Geoіnformatsіyniy monіtoring navkolishnogo seredovishcha [Proceedings of the IX-th International scientific and technical symposium "Geoinformation monitoring of environment], 2004, pp. 46–48.

3. Duma M., Savchin I. Optimіzatsіya konfіguratsіi ta rozmіshchennya punktіv opornoї GNSS-merezhі Dnіstrovskoї GAYeS [Optimizing configuration and placement of items GNSS reference network Dniester PSP], Mіzhnarodna Naukovo-Tyekhnіchna Konfyeryentsіya Molodikh Vchyenikh "GeoTerrace-2016" [Conf. proc. International Scientific Conference of Young Scientists "GeoTerrace-2016"], 2016, pp. 68–71.

4. Savchyn І. Optimіzatsіya aktivnikh geodezichnikh merezh monіtoringu іnzhenernikh sporud gіdroelektrostantsіy [Optimization of active geo¬detic monitoring networks Hydropower engineering structures]. Associate Professorship Thesis, Lviv Polytechnic National University, Lviv, Ukraine, 2015.

5. Sіdorov І., Perіy S., Sarnavskiy V. Viznachennya rukhіv zemnoї poverkhnі v rayonі Dnіstrovskoї GAYES suputnikovimi ta nazemnimi metodami [Determination of the earth surface movements in areas оf Dniester GNSS using satellite and ground geodetic methods], Geodynamics, 2015, no. 2(19), pp. 15–25.

6. Tretyak K., Sidorov I. Optymizacija pobudovy geodezychnoi' merezhi Dnistrovs'koi' GAES suputnykovymy radionavigacijnymy tehnologijamy [Optimization of building geodetic network of the Dniester HPPS satellite radio navigation technologies]. Suchasni dosjagnennja geodezychnoi' nauky ta vyrobnyctva [Modern achievements in geodetic science and industry]. Lviv: Lviv Polytechnic Publishing House, 2005, pp. 207–219.

7. Tretyak K., Sіdorov I. Sumіsne opratsyuvannya suputnikovikh і nazemnikh geodezichnikh vimіrіv visokotochnoї merezhі budіvnitstva Dnіstrovskoї GAYES [Co-processing of satellite and ground-based measurements of high precision geodetic network construction of the Dniester PSP], Vіsnik geodezії ta kartografії [Journal of Geodesy and Cartography], 2012, no. 3(78), pp. 6–9.

8. Tretyak K. Planuvannya ta optimіzatsіya GPS – vimіrіv u geodezichnikh merezhakh [Planning and optimization of GPS – measurements in geodetic networks], Vіsnik geodezії ta kartografії [Journal of Geodesy and Cartography], 2000, no. 3(18), pp. 7–13.

9. Al-Zubaidy R., Mahdi H.A., Hanooka H.S., Optimized Zero And First Order Design Of Micro Geodetic Networks, Journal of Engineering Sciences, 2012, vol.18, no.12, December, рр. 1344–1364.

10. Amiri-Simkooei A. Analytical first-order-design of geodetic networks. Iranian journal of engineering sciences, 2007, no. 1(1), pp. 1–14.

11. Amiri-Simkooei A. Strategy for designing geodetic network with high reliability and geometrical strength. Journal of surveying engineering, 2001, pp. 104–117.

12. Ayan T. Optimization of Geodetic Networks, Associate Professorship Thesis, Istanbul Technical University, Istanbul, Turkey, 1981. Berne´ J., Baselga S. First-order design of geodetic networks using the simulated annealing method. Journal of Geodesy, 2004, no. 78, pp. 47–54.

13. Liu H., He C., Zhang A., Liu H-x. GPS Technology Used in Three Gorges Reservoir Landslide Defor¬ma¬tion Monitoring. Journal of Yangtze River Scien¬tific Research Institute, 2008, no. 25, pp. 33–35.

14. Grafarend E. Optimization of geodetic networks. Bolletino di Geodesia a Science Affini, 1974, no. 33, pp. 351–406.