Egyptian Geoid Using Best Estimated Response of the Earth’s Crust due to Topographic Loads

Abstract

In this paper, the Egyptian gravimetric geoid is computed using the best estimated response of the earth’s crust due to the topographic loads. It has been proved that both the inverse isostasy approach and the direct isostasy approach (with Kelvin function $\mathop{\mathrm{kei}}\nolimits x$) give practically the same response of the earth’s crust due to topographic loads. The window remove-restore technique (Abd-Elmotaal and Kühtreiber, J Geod 77(1–2):77–85, 2003) has been used to avoid the double consideration of some of the topographic-isostatic masses in the neighbourhood of the computational point. The tailored geopotential model EGTGM2014 (Abd-Elmotaal, Egyptian geoid using ultra high-degree tailored geopotential model. Proceedings of the 25th international federation of surveyors FIG congress, 2014) has been used for the long wavelength contributions of the earth’s gravity field. The gravimetric geoid is computed for Egypt using Stokes’ integral in the frequency domain by 1-D FFT technique. For the sake of comparison, another geoid for Egypt using EGM2008 and Airy floating hypothesis has been computed. The computed geoids are scaled/fitted to the GPS-levelling derived geoid. The internal precision of the computed geoids is almost the same and it is at the level of 3 cm. The external accuracy of the geoid computed by the best estimated response of the earth’s crust is better by 4 dm.