Fitting gravimetric local and global quasi-geoids to GPS leveling data : The role of geoid quasi-geoid variations

Abstract EN

The Global Positioning System (GPS) has been extensively utilized in surveying and mapping applications worldwide and in Egypt, which results in a crucial need for precise geoid models.

Traditionally, global and local gravimetric quasi-geoid models are determined and, then, fitted to GPS / leveling data.

In the context of precise geoid determination, a quasi-geoid determination has to be converted to a geoid model prior to fitting process.

Neglecting such a transforming process leads to the absorption of these effects in the fitting residuals that, hence, may produce misleading results and interpretations.

The geoid / quasi-geoid separations in Egypt have been computed and found to range from –0.074 m to 0.367 m, with an average of 0.060 m.

Additionally, when the quasi-geoid to geoid conversion is performed, it has been found that the undulation of the EIGEN-CG01C global quasi-geoid model when compared to true undulations of HARN stations, have been decreased, in the mean sense, from 0.52 m to 0.46 m.

That means an average improvement of accuracy of about 11 %.

Based on the obtained results, it can be concluded that the conversion of the quasi-geoid to the geoid is quite significant and it should be a regular step in precise geoid determination in Egypt.