الفهرس 
Chapter One: IntroductionOnly 14 pages are availabe for public view
 |  | from | 240 |  |  |
| | | from | 240 | | |
Abstract
Recently, the concern in studying and defining local and regional geoid models worldwide has been wholly increased, as being necessary for height datum transformations. The broad spread of global navigation satellite systems in Egypt necessitates the development of a precise national geoid model in order to convert the ellipsoid-based geodetic heights into the MSL-based elevations. The current research aims to generate a new local geoid model for Egypt with high accuracy. The utilized datasets (containing 1010 terrestrial gravity stations, 1399 orthometric height points, and 941 GPS/levelling points) are the most-recent and most-accurate geodetic databases in Egypt for the time being, in terms of number, distribution, and precision, and they are utilized in geoid modelling for the first time. National geoid modelling requires the utilization of both Global Geopotential Models (GGMs) representing the long wavelength of the gravitational field of the Earth, and Digital Elevation Models (DEMs) used in topographic effects computations. Accordingly, several GGMs and DEMs have been investigated in order to judge their performance level of precision over Egypt. It has been found that the EGM2008 is the most precise GGM model in representing the gravity field of Egypt in terms of free-air gravity anomalies and geoidal undulations too. In addition, it has been found that the SRTM is the best global DEM representing the Egyptian topography. Utilizing the least-squares collocation geoid modelling method, the present study has developed two geoid models: the first model (named SRIGEOID16- 1) is based on all available refined terrestrial gravity measurements; and the second model (called SRI-GEOID16-2) relies on data from NGSBN-77 and ENGSN-97 networks only. For both models, the available GPS/levelling dataset has been incorporated along with the application of the EGM2008 GGM. It has been found that the actual accuracy level of SRI-GEOID16-1 geoid model, when compared to independent GPS/Levelling measurements, is 18.4 cm. On the other hand, the actual accuracy level of the SRI-GEOID16-2 geoid model found to be 12.5 cm. Moreover, the achieved findings conclude that SRI-GEOID16-2 geoid model is more accurate than its preceding, SRI-GEOID16-1, by almost 32 %. These enhancements are attributed principally to the exclusion of the nonprecise second-order gravity measurements. Additionally, SRI-GEOID16-2 geoid is found to be more accurate by almost 47% than the global EGM2008 model. That is accredited, as expected, to the incorporation of precise local geodetic datasets. Therefore, it can be concluded that the novel developed SRIGEOID16-2 geoid is the most accurate geoid model for Egypt for the time being. Indeed, there are no available published geoid models in Egypt that have reached such an accuracy level ( 13 cm) nationwide. Therefore, that innovative geoid model is recommended to be utilized in surveying, mapping, water resources management, and all other civil engineering activities in Egypt.