____________________________________________________________________________________________ Investigating the Precision of Recent Global Geoid Models and Global Digital Elevation Models for Geoid Modelling in Egypt Essam M. Al-Krargy, Magdy M. Hosny, and Gomaa M. Dawod Regional Conference on Surveying & Development Sharm El-Sheikh, Egypt, 3-6 October 2015 1 Investigating the Precision of Recent Global Geoid Models and Global Digital Elevation Models for Geoid Modelling in Egypt Essam M. Al-Krargy, Magdy M. Hosny, and Gomaa M. Dawod Survey Research Institute National Water Research Center, Egypt essamalkrargy@yahoo.com Abstract A national geoid model is crucial for a wide range of surveying and civil engineering applications worldwide, with Egypt being of no exception. Although there are many researchers attempted to develop a national Egyptian geoid model, the limitations of available geodetic data sized the precision of such models. In order to increase the accuracy of a geoid model, a precise Global Geopotential Model (GGM) along with a precise Digital Elevation Model (DEM) is needed. This papers aims to quantify the precision of most-recent released GGM and global DEM models based on a precise local geodetic dataset (gravity and GPS/Levelling data) covers the Egyptian territories. The attained results show that, out of seven investigated recent GGMs, the EGM2008 is the most precise global models over Egypt, that produces a mean standard deviation of geoid undulation differences equals ± 0.23 meter over observed 1074 GPS/Levelling stations. Additionally, the EGM2008 model gives a mean standard deviation of gravity differences that equals ± 25.1 mGal when examined over 941 observed gravity points. Furthermore, it has been shown that the SRTM3 DEM produces a mean standard deviation of ± 4.3 meter when compared over 1227 points of observed orthometric heights. Consequently, it is recommended to apply these two specific models in the undergoing development of a national geoid model of Egypt. Keywords: Geoid, Gravity, GPS, GGM, DEM, Egypt 1. Introduction A precise geoid model constitutes one of the most challenging research subjects of geodesy, particularly since 1980s. Geoid modelling deal with the determination of geoid undulations between the geodetic heights obtained from the Global Navigation Satellite Systems (GNSS) techniques and the orthometric heights, or levels, relative to the Mean Sea Level (MSL). Thus, geoid models are crucial for the utilization of GNSS (particularly the Global Positioning System: GPS) in civil engineering projects. Over the last two decades, national precise geoids have been developed all over the world, e.g. in Indonesia (Pahlevi et al. 2015), Uganda (Ssengendo et al. 2015), Korea (Lee and Kim, 2012), New Zealand (Classens et al. 2011), Sudan (Abdalla and Fairhead, 2011), and Italy (Corchete 2011). In Egypt, since the development of the first pioneer national-scale geoid (Alnaggar 1986), several geoid researches have been carried out. For example, Dawod (1998) has developed a national geoid model based on the data of the Egyptian National Standardization Network of 1997 (ENGSN97) along with GPS/levelling data. Saad and Dawod (2002) have developed a national geoid model