Henryk Jafernik, Janusz Ćwiklak, Kamil Krasuski and Jarosław Kozuba
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Chalermchon Satirapod, Punlop Payakleard, Wim J.F. Simons and Somchai Kriengkraiwasin
Since its introduction in 1990s, the GPS Precise Point Positioning (PPP) technique has been widely used for many high precision positioning applications such as the study of tectonic plate motion, establishment of national and regional reference frames and so on. Among the GPS PPP software packages, the GIPSY-OASIS II software package is the one of the most popular software package used by many research institutes worldwide. The processing of GPS data with the GIPSY-OASIS II software requires three main steps. The first step is to compute a daily GPS solution for each station and the second step is to combine daily GPS solutions into a multi-day averaged solution. The final step is to transform these multi-day averaged solutions into the International Terrestrial Reference Frame (ITRF) coordinate solution and this step generally requires the use of available International GNSS service (IGS) stations to compute the required transformation parameters. In order to obtain high precision ITRF coordinate solutions, an investigation on a selection of IGS stations used for aligning the multi-day averaged solution into ITRF is therefore needed. This study aims to investigate the effect of number of IGS stations used for aligning the multi-day averaged solutions into the final ITRF coordinate solution in Thai region. Data from two different GPS campaigns (with epochs before and after the 2004 Sumatra- Andaman earthquake) measured by the Royal Thai Survey Department (RTSD) were used in this investigation. By varying the number of IGS station used in the alignment step, results indicate that the use of at least 16 IGS stations in the alignment process can produce reliable and accurate ITRF solutions especially those impacted by the large earthquake.
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Geng, J., Teferle, F. N., Meng, X., and Dodson, A. H. (2010). Towards PPP-RTK: ambiguity resolution in real-time precise point positioning, Advances in Space Research, 47, 1664-1673.
Hadas T., and Bosy J. (2014). IGS RTS precise orbits and clocks verification and quality degradation over time, GPS Solutions, 19(1), 93-105
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Geng J., Teferle F.N., Shi C., Meng X., Dodson A.H., Liu J., (2009). Ambiguity
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Emad El Manaily, Mahmoud Abd Rabbou, Adel El-Shazly and Moustafa Baraka
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Hernández-Pajares et al. (2009), “The IGS VTEC maps: a reliable source of ionospheric information since 1998”. Journal of Geodesy, Volume 83, Issue 3-4, PP 263-275, March 2009. https://doi.org/10.1007/s00190-008-0266-1
Héroux, P., Y. Gao, J. Kouba, F. Lahaye, Y.Mireault, P. Collins, K. Macleod, P. Tétreault, and K. Chen (2004). “Products and Applications
Tropospheric delay is the second major source of error after the ionospheric delay for satellite navigation systems. The transmitted signal could face a delay caused by the troposphere of over 2m at zenith and 20m at lower satellite elevation angles of 10 degrees and below. Positioning errors of 10m or greater can result from the inaccurate mitigation of the tropospheric delay. Many techniques are available for tropospheric delay mitigation consisting of surface meteorological models and global empirical models. Surface meteorological models need surface meteorological data to give high accuracy mitigation while the global empirical models need not. Several hybrid neutral atmosphere delay models have been developed by (University of New Brunswick, Canada) UNB researchers over the past decade or so. The most widely applicable current version is UNB3m, which uses the Saastamoinen zenith delays, Niell mapping functions, and a look-up table with annual mean and amplitude for temperature, pressure, and water vapour pressure varying with respect to latitude and height. This paper presents an assessment study of the behaviour of the UNB3m model compared with highly accurate IGS-tropospheric estimation for three different (latitude/height) IGS stations. The study was performed over four nonconsecutive weeks on different seasons over one year (October 2014 to July 2015). It can be concluded that using UNB3m model gives tropospheric delay correction accuracy of 0.050m in average for low latitude regions in all seasons. The model's accuracy is about 0.075m for medium latitude regions, while its highest accuracy is about 0.014m for high latitude regions.
Ray J. R. (2009). On the precision and accuracy of IGS orbits, J. Geod. , doi: 10.1007/s00190-008-0237-6, 83, 277-287.
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Gross R. S. (2007). Combinations of Earth orientation measurements: SPACE2006, COMB2006, and POLE2006, JPL Pub. 07-5 , Jet