Determination and validation of the Turkish Geoid Model-2020 (TG-20)

A new hybrid geoid model for Turkey entitled Turkish Geoid Model-2020 (TG-20) has been determined and validated using historical and recently acquired terrestrial gravity and GPS/levelling data as well as the latest global geopotential and digital elevation models. Highly qualified new gravity data have enabled us to detect and correct some gross errors such as datum inconsistencies in the historical gravity data sets. The Least-Squares Modification of Stokes' formula with the Additive Corrections Method has been applied to compute gravimetric geoid model. Transformation to hybrid model has been carried out via 4-parameter fit to homogenously distributed historical GPS/levelling data. Quality assessment of the fit residuals has let us to find out some unrevealed outlying data in the historical GPS/levelling data set, which had already been utilised in the previous geoid model computations. Validation of the TG-20 over the seven different new GPS/levelling profiles has suggested standard deviations ranging between 1.2 and 6.3 cm, that is at least twice more accurate than the previous official geoid model. The results reveal that the recent measurement campaigns and the latest global models bring about a significant and substantial amount of improvement in computing and validating a high quality national geoid model.