@article{MAKHILLJEAS201813215443,
    title = {Comparison of Geoid Undulation Values Using Different Global
Geopotential Models over Egypt},
    journal = {Journal of Engineering and Applied Sciences},
    volume = {13},
    number = {2},
    pages = {441-451},
    year = {2018},
    issn = {1816-949x},
    doi = {jeasci.2018.441.451},
    url = {https://makhillpublications.co/view-article.php?issn=1816-949x&doi=jeasci.2018.441.451},
    author = {Tarek M.},
    keywords = {Geoid,undulation,GGM,ellipsoidal heights,orthometric heights,Egypt},
    abstract = {While the most challenge research scopes of geodesy/surveying science are to identify the highly
accurate three-Dimensional (3D) coordinates (φ, λ, h/H), the vertical positioning (h/H) are the most crucial for
many applications in civil engineering projects. These projects require to convert the Ellipsoidal height (h)
[observed by the Global Positioning System (GPS)] to orthometric Height (H) [observed by traditional field
survey techniques such as spirit levelling]. The difference between the ellipsoidal height (h) and orthometric
Height (H) called the geoid undulation or geoidal height (N). The Global Geopotential Model (GGM) is a model
that is being represented by the spherical harmonic coefficient that defines the potential of gravitational in the
spectral domain. Lately several GGM have been developed based on the accurate data collected by the different
satellite missions. Due to the importance of Egypt location, there are many efforts for applying (as international
projects) and/or modifying (as researches studies) several of these GGMs. Also, since, Egypt has area up to
one million km<sup>2</sup> and due to the limited input data for different GGMs, therefore ,the accuracy of the GGMs are
low. So, it&#146;s expected that the undulation values (N) will be different when using different GGMs. This paper
aim to study the relation between the undulation values (N) using most common eight GGMs. The study will
be on regular points distribution (346 point) between latitudes &phi; [22&deg;N, 31&deg;N] and between longitudes &lambda;
[26&deg;E, 36&deg;E] which cover whole Egypt territories. Generally, the maximum (N) value reach 21.47 m at [29.5&deg;N,
33.5&deg;E], the minimum value reach 7.23 m at [22.5&deg;N, 36&deg;E], the maximum difference of N calculated using deferent
GGM reach 6.08 m at [28.5&deg; N, 34&deg;E] and the minimum difference reach 0.36 m at [26&deg;N, 27&deg;E].}
    }