Associate professor of surveying and geodesy, Dept. of Public Works Engineering, Faculty of Engineering, Tanta University, Tanta City, Egypt
The author compares several methods to map the a priori wet tropospheric delay of GNSS signals in Egypt from the zenith direction to lower elevations.
Methods and Materials:
The author compared the following mapping techniques against ray-traced delays computed for radiosonde profiles under the assumption of spherical symmetry: Saastamoinen, Hopfield, Black, Chao, Ifadis, Herring, Niell, Moffett, Black and Eisner and UNBabc mapping functions. Radiosonde data were computed from radiosonde stations at the Egyptian stations; in the south of Egypt, near the Mediterranean Sea, and near the Red Sea over a period of 5 years (2000-2005), most of the stations launched radiosonde twice daily, every day of the year. Moreover, data is received from the Egyptian Meteorology Authority.
Results and Conclusion:
The results indicate that currently, the saastamoinen mapping function should be used for all geodetic applications in Egypt, and if necessary, the Chao and Moffett mapping functions can serve as an acceptable replacement without introducing a significant bias into the station position.
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* Address correspondence to this author at the Dept. of Public Works Engineering, Faculty of Engineering, Tanta University, Tanta City, Egypt; Tel: 040 3315860; Fax: (+20) 0403315860; E-mail: Sobhi100@yahoo.com