engleski

High Resolution Geoid Modelling of Croatia

The importance of the geoid surface was revealed along with the evolution of the Global Navigation Satellite Systems in the middle of 21st century. They have enabled the three dimensional positioning at every point around the globe. The only deficiency was that the generated height dimension was related to the reference ellipsoid. In order to transform the ellipsoidal height to the orthometric ones, the development of geoid model computation techniques was rampant. Today, the geoid surface can be determined with the centimeter accuracy. One of the main challenges in the physical geodesy today is achieving the millimeter geoid. Large efforts are being put in the determination of a millimeter geoid surface with the intention to define vertical datum regarding the geoid model in the near future. The biggest obstacle on that path is the lack of the terrestrial gravity data. Therefore, this thesis comprehended the examination of the optimal density of the terrestrial gravimetric data distribution in order to determine the geoid of millimeter accuracy. The study resulted with the optimal data density of $1$ point per square kilometer or higher, also showing that the determination of the millimeter geoid model is no longer a theory, but it can be achieved with that number of terrestrial data available. The geoid computed for this purpose was determined on the smaller area, resulting with the internal accuracy of +/- 9 mm and absolutely validated with the RMS of +/- 1 cm, which confirmed one of the hypothesis set for this PhD. Furthermore, the core of this study was the determination of the improved geoid model for the whole Croatian area. Taking into consideration the new methodology applied for the first time to the Croatian area, the improved geoid model was determined for the Croatian territory, with the RMS of $\pm3.9 \, cm$ for the internal control, and the RMS of $\pm4.7 \, cm$ for the absolute external accuracy assessment. The established geoid surface is determined in ultra high resolution of $30x30$ arc seconds, which corresponds to the resolution of less then $1 \, km$ in reality. With that resolution, it is the most detailed geoid model ever determined for the area of Croatia.

geoid; vertical datum; ellipsoid; terrestrial gravity data; accuracy; high resolution

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