Investigation of the effect of global geoid models on the results in determining local geoid with DFHRS approach

Nowadays, with the significant developments and advancements in GNSS technology, location accuracy has increased significantly. However, since the height measured by GNSS cannot be used directly in practice, the importance of the required geoid height accuracy is constantly increasing. For this reason, an attempt was made to meet this need with the local geoid determination method using the DFHRS approach. The DFHRS approach aims to solve the geoid height by evaluating the geometric and physical observation components together by ensuring the continuity of the polynomials within the finite elements between the parts. GNSS/Leveling data were used for geometric observations, and 4 different global geopotential models in the DFHRS database were used for physical observations. As the study area, the city center of Konya province and its surroundings were designed in 2x2, 5x5 and 10x10 km grid intervals and were divided into four separate sub-regions in the south-north and west-east directions. Thus, 48 different improved local geoid models were produced for the study area with the DFHRS approach. The results of the produced models were compared with the GNSS/Levelling geoid and subjected to model selection criteria and the best model was tried to be determined. In this sense, the improved local geoid model named 5X5EIGEN04DB, with a 5x5 grid space, segmented east-west direction and using the EIGEN04 global geopotential model, was determined as the best model with an RMSE value of ±1.93 cm. Using this model, geoid height was estimated for the study area at 500 m intervals through DFHRS software, and a geoid map was created, which users can switch from ellipsoid height to orthometric height.