Abstract
Validation of recent GOCE/GRACE geopotential models over Khartoum state - SudanThis paper evaluates a number of latest releases of GOCE/GRACE global geopotential models (GGMs) using the GPS-levelling geometric geoid heights, terrestrial gravity data and existing local gravimetric models. We investigate each global model at every 5 degree of spherical harmonics. Our analysis shows that the satellite-only models derived by space-wise and time-wise approaches (SPW_R1, SPW_R2 TIM_R1 and TIM_R2), GOCO01S together with EGM08 (combined model) are very distinct and consistent to the local data, which guarantees one of them to be selected as the best of candidate models and then to be utilized in our further geoid studies. One of Satellite-only models will be employed for acquiring the long wavelength geoid component which is one of major steps in the geoid determination. EGM08 will be used to compensate and restore the missing gravity data points in the un-surveyed parts within the target area. We expect further improvements in geoid studies in Sudan due to the improved medium wavelength part of the gravity field from GOCE mission.
Highlights
As many countries Sudan lacks adequate data for compilation of high resolution geoid, there are no enough GPS-levelling points yet, and most of the existing datasets is con dential and inaccessible
This paper evaluates a number of latest releases of Gravity eld and steady-state Ocean Circulation Explorer (GOCE)/Gravity Recovery And Climate Experiment (GRACE) global geopotential models (GGMs) using the GPS-levelling geometric geoid heights, terrestrial gravity data and existing local gravimetric models
Histograms of the differences between the terrestrial free air gravity and free air gravity derived from both EGM08 and EIGEN-GL04C are shown in Figures ??a and ??b
Summary
As many countries Sudan lacks adequate data for compilation of high resolution geoid, there are no enough GPS-levelling points yet, and most of the existing datasets is con dential and inaccessible. Salih (1983 and 1985) computed the geoid in Sudan using astrogeodetic and Satellite methods. During the computation process of the rst gravimetric geoid model for Sudan, the only existing reliable satellite only geopotential. The KTH method is based on combining the terrestrial gravity and GGM data by using the modi ed Stokes formula in least-squares sense (Sjóberg 1984, 1991, 2003a and 2003b). KTH-SDG08 was evaluated using 19 GPS-levelling points, showing a standard deviation (STD) of differences between the gravimetric and geometric geoid heights of about 0.3 m after applying 7-parameter model. The GGMs will be evaluated against the local gravity grid of Sudan
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