A gravimetric geoid for Egypt derived by FFT technique - EGGG2000

A set of all currently available free-air gravity anomalies in Egypt represents the gravimetric data set for this investigation. In the framework of the well-known remove-restore technique, a set of 30" x 30" and 3' x 3' Digital Height Models are used for computing the effect of the topography and its compensation on the gravity anomalies and on the geoid undulations (the indirect effect). The commonly used Airy-Heiskanen isostatic hypothesis is applied. The EGM96 global geopotential earth model is used for computing the effect of the reference field. A gravimetric geoid is computed for Egypt using Stokes' integral in the frequency domain by the multi-band spherical FFT technique. The computed geoid is compared with the geoid derived from the available GPS and levelling benchmarks in the data window. Removing a Kriging (collocation) trend function from the computed FFT geoid gives very good geoid precision for Egypt (about 2.5 cm). The external accuracy of the geoid in this case would be in the order of three decimetres.