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The maintenance of a modern vertical reference system in Bulgaria, aligned with the European Vertical Reference System (EVRS) standards, is directly dependent on the precise knowledge of the Earth's gravity field. The research presented in this paper is motivated by the 5th cycle of the 1st order National Leveling Network (NLN) re-measurement, initiated in 2021, which involves complex observations across 55 leveling lines. The primary objective of this study is to evaluate the extent to which existing gravity reso...

This paper is focused on the verification of two quasi-geoid models for the territory of Bulgaria (the model integrated into the Geodesy, Cartography and Cadastre Agency (GCCA) official product for the transformation of geodetic data and a model derived using the GNSS/levelling method) through direct geodetic measurements. The study was developed in the framework of the current 5th cycle of the 1st Order National Levelling Network (NLN), conducted in accordance with the requirements of the new 2021 Instruction [1]...