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    An Evaluation of Recent Global Geopotential Models for Strip Area Project in Turkey
    (Univ Nacional De Colombia, 2016) Doganalp, Serkan
    The aim of this study is to present the evaluations based on comparisons of geoid heights that are computed from several global geopotential models (GGMs) and the GNSS/levelling data. In this application framework, differences between geoid heights obtained by GGMs and GNSS/levelling were computed. Then, the availability of geoid heights calculated by GGMs for engineering applications were investigated. The Konya-Polatli (Ankara) Express Train Project as a strip area project was chosen as the study area. The length of the project is approximately 210 km and consists of 110 benchmarks that belong to the Turkish National Triangulation Network. In this study a total of 69 GGMs were compared. In order to examine more detail, these models were classified as three groups based on CHAMP, GRACE and GOCE. Each group was evaluated separately and the results were obtained. According to results, the best five models were detected for geoid height differences (NGNSS/lev-Nggm) in terms of standard deviation. These are EIGEN-6c4, EIGEN-GRACE01s, EGM2008, EIGEN-6c3stat and EIGEN-6c2, respectively. Also, geoid heights were obtained using different parametric models. These parametric models were used in order to minimize the impact of the terms of bias, tilt etc. Generally, three, four, five and seven parametric models are used for the least-squares adjustment of the geoid height differences in the literature. Therefore, in this study the geoid heights were calculated for such different parametric models. After the geoid height values were computed from the parametric models, the best global geopotential models in terms of standard deviation were obtained as EIGEN-6c2, EIGEN-6c3stat, EGM2008, EIGEN-6c4 and EIGEN-GRACE01s, respectively.
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    An Evaluation of Recent Global Geopotential Models for Strip Area Project in Turkey
    (Univ Nacional De Colombia, 2016) Doganalp, Serkan
    The aim of this study is to present the evaluations based on comparisons of geoid heights that are computed from several global geopotential models (GGMs) and the GNSS/levelling data. In this application framework, differences between geoid heights obtained by GGMs and GNSS/levelling were computed. Then, the availability of geoid heights calculated by GGMs for engineering applications were investigated. The Konya-Polatli (Ankara) Express Train Project as a strip area project was chosen as the study area. The length of the project is approximately 210 km and consists of 110 benchmarks that belong to the Turkish National Triangulation Network. In this study a total of 69 GGMs were compared. In order to examine more detail, these models were classified as three groups based on CHAMP, GRACE and GOCE. Each group was evaluated separately and the results were obtained. According to results, the best five models were detected for geoid height differences (NGNSS/lev-Nggm) in terms of standard deviation. These are EIGEN-6c4, EIGEN-GRACE01s, EGM2008, EIGEN-6c3stat and EIGEN-6c2, respectively. Also, geoid heights were obtained using different parametric models. These parametric models were used in order to minimize the impact of the terms of bias, tilt etc. Generally, three, four, five and seven parametric models are used for the least-squares adjustment of the geoid height differences in the literature. Therefore, in this study the geoid heights were calculated for such different parametric models. After the geoid height values were computed from the parametric models, the best global geopotential models in terms of standard deviation were obtained as EIGEN-6c2, EIGEN-6c3stat, EGM2008, EIGEN-6c4 and EIGEN-GRACE01s, respectively.
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    GEOID HEIGHT COMPUTATION IN STRIP-AREA PROJECTS BY USING LEAST-SQUARES COLLOCATION
    (Acad Sci Czech Republic Inst Rock Structure & Mechanics, 2016) Doganalp, Serkan
    GPS/leveling technique is the most effective engineering method for the determination of heights and height differences. This method is based on the principal of conversion of ellipsoid heights to orthometric heights. For transformation, polynomial surface models are generally used for study region or area. The accuracy of results depends on the location and distribution of selected reference stations with known ellipsoidal and orthometric heights. Especially, in the strip area projects (highway, railway, channel etc.) polynomial curve model is used instead of polynomial surface model due to reference stations disturbing along a route. In this research, Least Squares Collocation (LSC) methods used in determining the geoid heights of a strip area were examined. For this purpose, GPS/leveling data of Bozkurt-Dinar (Afyonkarahisar) train project which is approximately 75 km was used in order to examine LSC methods. The ground control stations of the project were classified as reference and test for the purpose of this research. The geoid heights of test stations were calculated by curve polynomial with different degrees. Additionally geoid heights at the same points were calculated using polynomial curve fitting based on LSC which is suggested by this research. The geoid heights by computed using LSC approach when compared to polynomial curve method were observed to yield better results.
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    GEOID HEIGHT COMPUTATION IN STRIP-AREA PROJECTS BY USING LEAST-SQUARES COLLOCATION
    (Acad Sci Czech Republic Inst Rock Structure & Mechanics, 2016) Doganalp, Serkan
    GPS/leveling technique is the most effective engineering method for the determination of heights and height differences. This method is based on the principal of conversion of ellipsoid heights to orthometric heights. For transformation, polynomial surface models are generally used for study region or area. The accuracy of results depends on the location and distribution of selected reference stations with known ellipsoidal and orthometric heights. Especially, in the strip area projects (highway, railway, channel etc.) polynomial curve model is used instead of polynomial surface model due to reference stations disturbing along a route. In this research, Least Squares Collocation (LSC) methods used in determining the geoid heights of a strip area were examined. For this purpose, GPS/leveling data of Bozkurt-Dinar (Afyonkarahisar) train project which is approximately 75 km was used in order to examine LSC methods. The ground control stations of the project were classified as reference and test for the purpose of this research. The geoid heights of test stations were calculated by curve polynomial with different degrees. Additionally geoid heights at the same points were calculated using polynomial curve fitting based on LSC which is suggested by this research. The geoid heights by computed using LSC approach when compared to polynomial curve method were observed to yield better results.
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    Local geoid determination in strip area projects by using polynomials, least-squares collocation and radial basis functions
    (Elsevier Sci Ltd, 2015) Doganalp, Serkan; Selvi, Huseyin Zahit
    Orthometric heights are used in many engineering projects. However, the heights determined by the widely-used Global Navigation Satellite System (GNSS) are ellipsoid heights. Leveling measurements conducted with the purpose of determining the orthometric heights on points are quite arduous and time-consuming processes. To be able to use ellipsoid heights in engineering projects, their transformation to orthometric heights defined in the height datum of the region is necessary. Therefore, in terms of convenience and feasibility GNSS/levelling method is preferred in determining geoid heights. This method is based on the principle of transformation of ellipsoid heights to orthometric heights. In effect, the main purpose of the method can also be regarded as the estimation of geoid undulation values for the study area. During the estimation process, polynomial (surface, curve) models are generally used. Polynomial models produce meaningful results for points which are scattered uniformly on the study area. However, for strip areas where the points scatter along a route (road etc. projects), the accuracy of the geoid heights obtained from these models is low. Therefore, different estimation techniques have to be implemented in strip areas instead of polynomial models. In this study, interpolation methods used in determining the geoid undulation of a strip area were researched and the identification of the best suitable method for the area was examined. For this purpose, geoid undulation values were calculated with the help of least-squares collocation (LSC) and radial basis functions such as Multiquadric (MQ), Thin Plate Spline (TPS) along with polynomial models, and results were presented. According to the results, it was observed that TPS, MQ, LSC methods respectively yield better results compared to polynomial methods. (C) 2015 Elsevier Ltd. All rights reserved.