# The Science Of Determination The Figure Of The Earth

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CHAPTER 1 INTRODUCTION 1.1 Research Background: Geodesy is considered, according to Bruns (1878) and Helmert (1884), as the science of determination the figure of the earth as well as its gravitational field. This covers the basic general form of the earth as a flattened rotational ellipsoid and the visible topographic surface resulted from gravitational attraction of uneven inner masses. Thus, physical and geometric aspects are inseparably correlated (Moritz 2015). In geodesy, the figure of the earth refers to the figure extracted physically or mathematically from the true surface of the earth (Moritz 1990). This includes the geoid and the reference ellipsoid along with the normal ellipsoid. While the geoid can be interpreted as the physical figure of the earth, the reference ellipsoid can be considered as the mathematical figure of the earth, and the normal ellipsoid can be considered as the mathematical and physical figure of the earth. However, the reference ellipsoid and the normal ellipsoid are a close approximation of the geoid. Hence, the figure of the earth studied in geodesy mainly refers to the figure of the geoid (Lu et al. 2014). Geoid is defined as an equipotential surface of the earth 's gravity potential, where the mean surface of the oceans particularly forms a part (Hofmann-Wellenhof and Moritz 2005). On oceans, the geoid agrees with the mean sea surface, more precisely, with a calm ocean surface subjected only to the force of gravity, which is assumed