الفهرس 
Semi-Dynamic Datums
Assessment of Di?erent Approaches of Dynamic/Static Datum Transformation in EgyptOnly 14 pages are availabe for public view
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Abstract
In this work, two critical geodetic issues in Egypt were discussed. Firstly, the dynamic nature of International Terrestrial Reference Frame (ITRF) as a geodetic datum, while the main Global Posi- tioning System (GPS) network in Egypt is tied to a static datum is considered a critical geodetic issue. Tying any derived ITRF coordinates to the Egyptian network cannot be directly applied due to the effect of the tectonic plate motion, in addition to the datum definition change from one ITRF realization to another. The simplest solution is neglecting the effect of the datum def- inition change and using a Plate Motion Model (PMM) for the backward propagation of coordinates until the specified epoch of the static datum. However, the most opportune solution is apply- ing the 14-parameter datum transformation. In this study, a new set of 14 parameters was derived to describe the transformation process of the African plate in a better way. Assessment the qual- ity of both solutions based on recent Global Navigation Satellite System (GNSS) observations, for 4 stations from the Egyptian network, was presented. In addition, 5 different PMM(s) were used to assess the compatibility of the recent PMM(s) with the
actual plate motion in Egypt. This study showed that using the derived parameters in the 14-parameter model gives the best results. In addition, using APKIM2005D or ITRF2008-PMM as the adopted PMM gives the best results, while using NNR- MORVEL56 gives the worst results. For the horizontal compo- nent differences, the 14-parameter model with the derived param- eters approach can reach 1.3cm with Root Mean Square (RMS) 3.1cm in case of using APKIM2005D and 1cm with RMS 2.3cm in case of using ITRF2008-PMM. On the other hand, for the ver- tical component differences, they ranged from 0.8cm to 10.9cm with RMS 8.6cm. Generally, using the derived parameters in the 14-parameter transformation model adopting APKIM2005D or ITRF2008-PMM as the used PMM can be applied to any re- cently derived coordinates, tied to the latest ITRF realization, to tie them to the Egyptian static datum.
Secondly, in another context, an approach of tying new sta- tions to the Egyptian Continuous Operating Reference Stations (CORS) network using International GNSS Service (IGS) sta- tions and PMM(s) was assessed. A new continuous operating station at Faculty of Engineering, Ain Shams University was used in this study. Tying this station to the Egyptian CORS network was performed using GNSS observations for five stations from the Egyptian CORS network, obtained from the Egyptian Sur- vey Authority (ESA), and the resulted solutions were used as the reference in the assessment process. Four days in June 2017 were used. In addition, 24 hours observation periods and 4 hours ob-
servation periods (day and night) were evaluated. The quality of using this approach was assessed using 5 different PMM(s). The results showed that all PMM(s) give, almost, the same horizon- tal component accuracy with differences within few millimeters and only NNR-MORVEL56 deviates away from the other mod- els by almost 1cm. Considering the 4 PMM(s) that give almost the same results, the resulted mean horizontal differences ranged from 1.9cm to 2.3cm, from 2.4cm to 3.1cm and from 2cm to 2.1cm in case of using 24h, 4h (day hours) and 4h (night hours) obser- vation periods, respectively. Regarding the vertical component differences, the mean differences were 5cm, 5.4cm and 7.4cm in case of using 24h, 4h (day hours) and 4h (night hours) obser- vation periods, respectively. Generally, using this approach in tying new stations to the Egyptian CORS network can achieve very promising results and help to avoid many administrative restrictions and additional costs. Also, the 4 hours observation periods can achieve promising results which make it applicable to the different surveying works performed in Egypt.