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Authors: Abdallah, Ashraf
Title: Precise point positioning for kinematic applications to improve hydrographic survey
Issue Date: 2016 Dissertation 152
Abstract: Recently, there is an increasing interest to obtain cost-effective and accurate coordinates using the technique of GNSS Precise Point Positioning (PPP). This technique is mainly based on utilizing just one dual frequency GNSS instrument. The hydrography has the main interest in the field of positioning using the GNSS technique. The precise hydrographic surveying causes a better estimation for the bathymetric survey, which provides a vital estimation for the level of the bed of water resource and detects soil sedimentations and obstacles. The current study investigates the performance of the kinematic PPP solution using Bernese GNSS software from two sides. The first side relates to the effective parameters that affect the PPP solution, and the second side to its performance for the hydrographic applications. The accuracy of the PPP solution is affected by the interval of the satellite clocks, especially, for the high rate kinematic data. There are a lot of studies concerning the impact of the satellite clocks on the static PPP solution. On the other hand, few studies regarding real kinematic measurements are published. Therefore, the current study focuses on this impact on the kinematic measurements and improves the estimated accuracy using Bernese GNSS solution. In order to evaluate this parameter, the final satellite clocks from CODE (Centre of Orbit Determination in Europe) with an interval of 30 s and 5 s have been investigated. Regarding this impact, two groups have been processed. Each group includes static data and kinematic hydrographic measurements. The first observation group had a sampling rate of 5 s. The first data set is based on four CORS (Continuously Operating Reference Station) stations showing with satellite clocks of CODE/5 s, a mean RMS error of 1.30 cm, 1.70 cm, and 3.35 cm for the East, North, and height, respectively. This solution provided better accuracy of 70% than that obtained from the default solution using CODE/30 s. In comparison with the adapted solution from Bernese for CODE/30 s, the solution of CODE/5 s achieved a better solution of 25% in the East, 40% in the North, and 12% in the height. Regarding the hydrographic measurements that were observed on the River Rhine, Germany, the solution showed for the satellite clocks of CODE/5 s, a mean root mean square (RMS) error of 4.73 cm, 3.90 cm, and 6.77 cm for the East, North, and height directions, respectively. In comparison with the default solution of CODE/30 s, the solution of CODE/5 s provided an improvement of 50% in the horizontal and 70% in the height. In comparison with the modified solution of CODE/30 s, the solution of CODE/5 s delivered 25% improvement in the horizontal component and 45% in the height. The second observation group had a sampling rate of 1 s. The first data set of four CORS stations obtained consequently a mean RMS error of 2.43 cm, 2.15 cm, and 6.10 cm for the East, North, and height. The default solution from Bernese GNSS software of CODE/30 s provided very high errors; therefore, the modified solution of CODE/30 s was considered. The solution of CODE/5 s provided an improvement of 10% compared to CODE/30 s. Furthermore, for the second data set of the hydrographic data that was measured on the River Nile, Egypt, the solution achieved a mean RMS error of 2 cm to 3 cm in the horizontal component, and 5 cm for the height component. This solution provided a better solution compared to the solution obtained from CODE/30s with a percentage of 15%, 40%, and 35% for the East, North, and height directions, respectively. A further parameter which is affecting the PPP solution is the zenith troposphere delay (ZTD). Three troposphere models have been investigated: the NIELL model, the Vienna Mapping Function (VMF1) model and the Global Mapping Function (GMF) model. 45 global IGS’s stations have been investigated. These stations cover different climates over the world. The results showed that the variation in the estimated height between the models is in the level of sub-mm to 1 mm; only for the Antarctica region, the NMF showed a worse solution than others. In addition, the real hydrographic measurements do not provide a significant coordinate solution difference between the three models. Since the water level is theoretically stable for the shallow water resources, the PPP estimation approach can be extended to enhance the obtained positions. The approach is based on constraining of the height for the hydrographic measurements by a specified standard deviation. The first solution was established using the assumption of the stable water level. The procedure is applied for a hydrographic trajectory that was observed on the Rhine River. The solution did not achieve any improvement due to the high variation of height during measurement. The solution is extended by considering a piecewise stability of the water level. Three hydrographic trajectories that provided without constraining a RMS2D position of 7 cm to 10 cm were processed concerning this concept. Two trajectories were observed on the Rhine River and one trajectory was surveyed on the Nile River. The trajectories were divided into different sessions; each session had a mean height, a standard deviation (σ), and a number of epochs (t). After applying the height constraining with the concept of piecewise stability of water level for these trajectories, the achieved RMS2D position after height constraining was 4.7 cm to 8 cm. This means that the RMS2D position is improved by 16% to 35%.
Appears in Collections:06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

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