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الجمعة، 24 نوفمبر 2017

Toward a Centimeter-Geoid Model for Engineering Surveying in Egypt: Status and Projected Activities


Toward a Centimeter-Geoid Model for Engineering Surveying in Egypt: Status and Projected Activities 

Gomaa M. Dawod*, Magdy M. Hosny 

Survey Research Institute, National Water Research Center, 308 Al-Ahram St., Talbiam Giza 12111, Egypt

Journal of Scientific and Engineering Research 312 Journal of Scientific and Engineering Research , 2017, 4(10):312-319 
Available online www.jsaer.com 
Research Article ISSN: 2394-2630 CODEN(USA): JSERBR


Abstract 

  With the broad spread of Global Navigation Satellite Systems (GNSS) utilization in geomatics and engineering surveying in Egypt in the last two decades, a precise geoid model becomes an essential demand. This paper investigates the possibilities of using global or local geoid models for height conversion in engineering activities. It has been found that most Global Geopotential Models (GGMs) could not depict the gravitational field over Egypt with a precision level less than 0.20 meter. On the other hand, recent available local geoid models still suffer from several factors and their accuracy still in the range of 0.10-0.15 meters. Precise surveying projects necessitate a more-accurate geoid model. As a result, the Survey Research Institute (SRI) has initiated a national collaborative effort to develop a centimeter-level hybrid geoid model for Egypt. So, three new geodetic networks; namely GNSS, levelling, and gravity, will be established on a national basis with first-order geodetic specifications and a reasonable grid spacing. The project aims to develop a national geoid model with a few-centimeter accuracy in the first phase, which can be modified later to achieve the one-centimeter accuracy level. Status of geodetic infrastructures and geoid modelling in Egypt, along with the projected geospatial activities are presented in details in this paper. 


Keywords: GNSS Surveying, Gravity, Levelling, Geoid, Egypt

5. Conclusions 

  In engineering surveying, the transformation of GNSS-based geodetic heights to the MSL-based orthometric heights requires a precise geoid model. On a national basis over Egypt, the most available geoid models produce an accuracy levels of 0.10-0.15 m. On the other hand, the utilization of GGM models gives errors in the order of more than 0.20 m. That accuracy is, by default, not appropriate for engineering activities. The main reason behind this situation is the lack of precise and homogeneously-distributed geodetic database over the country. Based on several workshops organized by SRI, it has been found that the optimum strategy is the unification and integration of all available resources and capabilities in carrying out a national project for developing a geoid model for Egypt. In this paper, the proposal is discussed in details including the strategy and technical procedures for conducting that effort. The anticipated project intends to develop a national geoid model with a few-centimeter accuracy in the first phase, which can be modified later to achieve the one-centimeter accuracy level. From an economic perspective, a national geoid model will broaden the utilization of GNSS positioning techniques in engineering applications in Egypt, and significantly decrease their costs compared with the time-consuming and expensive terrestrial surveying methods.

References

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