科研之友
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摘要
Sudan is characterized by vast area with flat terrains in most of the country's regions and therefore the existence of a high-resolution geoid model is considered very important especially with the widespread of the GPS technology in the country. A few studies were previously conducted to compute a geoid model for Sudan, the current study is the second of its kind to compute the Sudanese geoid model by means of gravimetric method. In this study, a new gravimetric geoid model (KTH-SDG08) is computed for Sudan, we apply the method developed at the Royal Institute of Technology (KTH) Stockholm-Sweden. The method utilizes the least-squares modification (LSM) of Stokes formula providing three stochastic solutions (biased, unbiased and optimum). The three solutions are quite similar however in this study we select the optimum solution which provides the best agreement with GPS-levelling data. The modified Stokes formula combines the regional terrestrial gravity data together with the long-wavelength gravity information from a global gravitational model (GGM). We use two sets of regional gravity data: the first set is provided by the GETECH, the points of this set cover discretely some parts of Sudan while the rest of the country's area are still not covered, the second set was provided by BGI contains a few points scattered over the neighbouring countries. Both datasets (GETECH and BGI) are unified together into one dataset and evaluated by Cross validation technique. Due to the lack of gravity observations we construct our final grid for geoid computation with spatial resolution of 5 x 5 arc-min. The long-wavelength contribution is donated by two geopotential models, EIGEN-GRACE02S satellite-only model is employed in the modified Stokes formula whereas the EIGEN-GL04C combined model is used to enrich the local gravity coverage over the areas with missing data. The Digital Elevation Model (DEM), SRTM generated by NASA and the National Imagery and Mapping Agency (NIMA) is used to compute topography effects on the geoid. Four additive corrections are computed over the entire target area and applied to the approximate geoid heights obtaining the final geoid solution. The new Sudanese gravimetric geoid model KTH-SDG08 is computed on a 5 x 5 arc-min geographical grid over the computation area bounded by the parallels of 4 and 23 arc-deg northern latitude, and the meridians of 22 and 38 arc-deg of eastern longitude. The gravimetric geoid is validated using GPS-levelling information at 19 points distributed over the whole country. The results show that the standard deviation (STD) of differences between the gravimetric and geometric geoid heights at 19 GPS-levelling points is about 0.3 m.
- 出版日期2011-6
