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This paper tests dedicating GPS as a leveling tool at a leveling line at the Northwestern part of Lake Nasser. The selected region has both geological and geodetic of interests. Test has been made by determining orthometric height from GPS height utilizing different geoid models. A total of 3 different gravimetric geoids: EGM96, EGM08 and local one...
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Citations
... is an adequate method for determining the height difference. This method has been increasingly used since the late nineties of the last century, where the satellite based Global Positioning System (GPS) has enrich the geodesy and surveying fields by a practical, economic and accurate tool for 3-D positioning determination (Alnaggar and Dawod, 1999;El-Ashquer et. al., 2010;El Shouny et al., 2017). After collecting the 3D points, an interpolation technique can be used to generate the digital terrain model (DTM) surface to represent the terrain topography of the concerned area. ...
... To generate a DTM for the coastal area, a set of kinematic GPS points will be collected and adjusted to the local vertical datum. This technique is applicable for such areas, as illustrated in Alnaggar and Dawod (1999), El-Ashquer et al. (2010) andEl Shouny et al. (2017). The collected points, then, will be interpolated using an appropriate interpolation technique. ...
ABSTRACT
Coastal zones are the most influenced areas by global sea level rising. One of the important coastal zones in Egypt is the Red Sea. Red Sea coastal area is an attractive touristic area, which still under development. For the high value of such areas, the position of the set-back construction line is required for well planning and development. This position influenced greatly by the position of the shoreline at the maximum retreating. This paper introduces an automatic approach for determining the shoreline at the maximum retreating. This approach depends on three types of information; 1) the location of the current shoreline, 2) the mean higher high-water level (MHHWL), and 3) the topography of the coastal area.
A study area North of Hurghada, is selected to apply the introduced approach. The shoreline is extracted out of Landsat-8 images based on a combination of three factors; a modified normal difference water index, the reflectance values of the water bodies in specific bands within the shortwave infra-red spectrum, and the relation of the reflectance values of water bodies in the Green, Red, NIR, and SWIR bands. The higher high-water level is determined from near tidal gauge station that has collected data each 30 minutes since 2008, and the topography of the coastal area is determined by the Kinematic GPS technique. The extracted shoreline was assessed by comparing it to actual shoreline traced on the ground. The results show that the accuracy of the extracted shoreline is within 15m of the actual shoreline.
... Accordingly, the transformation of the ellipsoidal height to an accurate orthometric height has become a concern for many geodesists. This transformation is mainly based on the basic relationship between ellipsoidal heights, ℎ, and orthometric heights, í µí°», as follows ( Figure 1) (El-Ashquer, 2010). ℎ = í µí°» + í µí± (1) where: ...
... In addition, the computation of geoidal height, N, which is known by geoid determination, gives rise to further systematic errors due to the neglect of short wavelength of the local gravity field. The short wavelengths of the gravity field can be deduced from local gravity data and terrain models (El-Ashquer, 2010). ...
The main objective of this study is to examine the concept and techniques of involving geoid in GPS height
observation to be detected as a leveling tool. The paper extends to the relationship between the obtained heights
and the use of the modern global geoid model EGM2008 available for the study area (Hilla, central Iraq). The
present analysis was carried 22 points observed by GPS and level devices available in the study area. Evaluation
by comparisons of geoid heights computed from the model with those available GPS leveling stations of the study
area were determined. Then, the standard deviations are calculated as an indicator for the accuracy of the US
website OPUS for the study area. Most accurate results of GPS data are obtained using the static method in
geodetic works after being processed through the US website OPUS. The results accuracy of the data observed
by GPS after processing by EGM2008 model is within the range ± 0.041 m. Finally, as an evaluation, it can be
stated from results of the computed geoid accuracy is acceptable and the present geoid model EGM2008 is
considered as the optimal geoid so far for the study area.
... e achieved accuracy made GPS a valuable leveling tool, is increased when using free air gravity data with high resolution local geoid model for the studied region. A much lower accuracy is obtained, when using global models, but still applicable for some cases. However, it is clear that EGM2008 model has a great advantage compared with EGM96 model (El-Ashquer. et al., 2010). 92 Because of the non-well distributed orthometric benchmarks in the studied area, GPS can be dedicated as a height control. However, heights from GPS can be converted to orthometric height only if we have an accurate local geoid in the studied region. Global geoid models can give the geoid heights in many regions, but these models ign ...
A Thesis
Submitted in Fulfillment of the Requirements to
Faculty of Engineering, Zagazig University
for the Degree of Master of Science in
Construction Eng. and Utilities
Different approaches were used in the analysis and computation the geoid model, such as GPS/Leveling, Bouguer and Free air anomalies.
The present analysis was carried on 21 gravity stations and 22 points observed by a GPS and level devices available in the study area. Due to the lack of precision of the satellite data (DTED90, DEM90, and DEM30), so
they cannot be relied in calculating terrain correction or the residual terrain model. Consequently, topographic maps were used to provide an accurate RTM for the study area. Hammer chart was used for the computation of
terrain correction precisely. The attained results of the DTED90 with or
without the addition of the undulation value showed the most precise model achieving the best accuracy within the area.
The accuracy of geoid was also estimated by comparing the GPS/leveling method with the geoid undulation EGM2008 model for the study area. The results revealed accuracy within ± 0.034 m for the geoid undulation.
As well as, this study stated the effect of gravity on the values of geoid undulation data. Bouguer and Free air anomaly values of the study area were compiled from the observed gravity database after processing. The residuals of both Bouguer and Free air anomalies were determined. The Remove – Compute – Restore (RCR) techniques were used to compute the gravimetric geoid undulation. The attained accuracies for both anomalies were around ± 0.019 m and ± 0.024 m, respectively. Thus, better results are achieved using Free air anomaly in calculation of the gravitational geoid as it is closer to the undulation accuracy extracted from the GPS/leveling method ± 0.034 m.
Due to the importance of the subject and for the lack of such studies in Iraq, this research attempts to determine the accuracy of the geoid based on the available GPS and gravity data for the study area (Hilla, Iraq). To assess the geoid model accuracy, undulation measurements for terrestrial points in the area are compared with the undulation values resulted from the global model. Then, the standard deviations are determined which will be the indicator for the accuracy of the global model. The present analysis was carried on 21 gravity stations and 22 points observed by a GPS and level devices available in the study area.
