Local geoid model of the Western Desert in Egypt using terrestrial gravity data and global geopotential models

Abstract

The local hybrid geoid model for the western desert in Egypt is computed by recent data, including the global geopotential models, gravimetric measurements, and a high-resolution digital topographic model. The research points out the importance of accurate local geoid computation not only as a survey datum but also to figure out the crustal structure. Detailed crustal structure patterns could reveal the origin of artesian aquifers and geothermal activities of the selected region. In this research, recent global geopotential models deduced from recent satellite missions have been used. The oases’ area of the western desert in Egypt is characterized by an irregular topographic pattern suggesting a complicated geoid model. Six recent global geopotential models (GGMs) have been evaluated for long and medium wavelengths. GGM accuracy for each model has been computed using GPS leveling data. EIGEN-6C model with spherical harmonic expansion to degree 250 gives the smallest error with a standard deviation equal to 0.019mGal. Also, a high-resolution digital topographic model with 3arcsec is used for terrain correction (Tc). The resulting geoid has been evaluated using GPS leveling in the selected region. Due to the recent geopotential models with high accuracy, the random distribution and low terrestrial gravity data have not become a problem in calculating the local geoid model.