Abstract
The determination of geoid models with great precision (centimeter) was always at the center of interest in geodesy research [1] [2]. One of the most used methods to calculate the geoid model is the method called Remove-Compute-Restore (R-C-R). This method applies the stokes’ integral formula by the use of short, medium and long wavelength information via the three main stages R-C-R. The GravSoft software implemented by [3] was used for this study. Geodetic heights, a digital terrain model (SRTM) and leveled GPS points were used as inputs. The geoid modeling was carried out on the North region of Tunisia (Grand Tunis and Bizerte) on an area of 83 × 83 km. The accuracy of the quasi-geoid provisional reached 3.1 cm.
Highlights
The most accurate approximation of the actual shape of the earth is the geoid
-The calculation is made by assimilating the geoids to a plane passing closer to the points of support and by calculating the distance between the searched point and the plan modeling the geoids. 28 points of the place on all Tunisia are used as points of support what gave a maximum error of 45 cm on the point of Gsar Ghilene and a standard deviation of 22 cm on the 28 points
As mentioned in the general process of the R-C-R method (Figure 5), the gravimetric anomalies used in the calculation are the free air anomalies, their determination is ensured by a translation of the Somigliana and free air formulas described above which give the value of g0 and the value of the anomalies
Summary
The most accurate approximation of the actual shape of the earth is the geoid. It is so called equipotential surface of gravity field [4]. It is affected by hollows and bumps, it is completely irregular. We can imagine it as being the average level of the oceans and its imaginary extension under the continents. The geoid, whose mathematical definition is relatively complex, is not very easy to use. Its use was mainly reserved for research on vertical references and mean sea level [5] [6]. The precision is estimated at 17.5 cm/100 km. In 2004, establishment of a local geoids model over the Tunis area by adjusting the global model EGM96 to GPS-derived leveling points, this model had a standard deviation of 10 cm. -The calculation is made by assimilating the geoids to a plane passing closer to the points of support and by calculating the distance between the searched point and the plan modeling the geoids. 28 points of the place on all Tunisia are used as points of support what gave a maximum error of 45 cm on the point of Gsar Ghilene and a standard deviation of 22 cm on the 28 points
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