الفهرس 
The GeoidOnly 14 pages are availabe for public view
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Abstract
The thesis attempts to find out an optimum combination of gravity field wavelengths in the geoid determination process for Egypt in the framework of the remove-restore technique. Different approaches for such a combination of the wavelengths exist. The modified Stokes kernel with different approaches and least square modification of Stokes’ formula have been suggested to possibly combine the local data signals with the global geopotential earth models. The window technique (Abd-Elmotaal and K htreiber 2003) has been suggested to get rid of the double consideration of the topographic-isostatic masses within the data window. These techniques have been used in determining a gravimetric geoid for Egypt.
A wide comparison between modified Stokes’ kernel with different approaches, least square modification of Stokes’ formula and window techniques have been carried out within this investigation in the framework of the geoid computation. The comparison is made on different levels. The contribution of the reference field on gravity anomalies, the contribution of the topography and its compensating masses on gravity anomalies, the residual gravity anomalies after the remove step, the contribution of the reference field on geoid undulation, the contribution of the topography and its compensating masses on geoid undulation, gravity contribution on geoid undulation, and the required computing time for the gravity contribution. The computed geoids have been compared to the GPS/levelling derived geoid. Finally, all the computed geoids have been fitted to the available GPS/levelling stations using a third order surface polynomial. The obtained results proved that the reduced gravity anomalies using the window remove-restore technique are the smoothest (have the smallest standard deviation), un-biased and have the smallest range. This property makes the window reduced anomalies suit best for interpolation and other geodetic purposes. The statistics of the absolute geoid differences between the computed geoids within the current investigation and the GPS/leveling derived geoid proved that the un-modified Stokes geoid has the worst differences to the GPS/levelling derived geoid. This confirms that using the classical un-modified Stokes kernel in the remove-restore technique implies a wrong combination of the gravity field wavelengths. The results shows that either using the window remove-restore technique or the modified Stokes kernel gives better differences to the GPS/levelling derived geoid (in terms of the standard deviation difference). The statistics of the remaining residual at the GPS stations shows that the window technique gives the best precise geoid (internal precision) in terms of both standard deviation and range. It is recommended to use the window remove-restore technique in determining the gravimetric geoid for Egypt as it can correctly handle the combination of the geoid wavelengths in an unambiguous way.