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Öğe COMPARISON OF REGIONAL AND GLOBAL TEC VALUES: TURKEY MODEL(SELCUK UNIV PRESS, 2018) Basciftci, F.; Inal, C.; Yildirim, O.; Bulbul, S.The ionosphere is a layer of atmosphere 60 km to 1100 km above the earth and is composed of solar rays and ionized gases. The ionosphere is an important layer affecting Global Navigation Satellite System (GNSS) measures. The quality of GNSS measures is directly related to the changes in the ionosphere. For this reason, monitoring changes in the ionosphere is quite important. One of the important parameters expressing the characteristic of the ionosphere is the Total Electron Content (TEC), which is a function of electron density exhibiting transformation with solar radiation. In this study, 68 stations including 56 Continuously Operating Reference Stations-Turkey (CORS-TR) stations and also IGS stations were taken for evaluation. Bernese v5.2 GNSS software developed by Bern University of Switzerland was employed at the evaluation stage. From 2009 until 2015, TEC values were calculated at two hourly intervals, one day for each month. In the study, where a Single Layer Model was used, TEC values obtained from GNSS measurements have been compared with the TEC (IRI-2012 TEC) values obtained from the global ionosphere map (GIM-TEC) and the international ionosphere reference model programme published by the Centre for Orbit Determination in Europe (CODE), the European Space Agency (ESA), and the Jet Propulsion Laboratory (JPL). As a result, the regional (RIM) TEC values and the global (CODE, ESA, JPL) TEC values showed a large similarity, and the IRI obtained TEC values remained lower than these four values was observed. Correlation coefficient was calculated to determine the relationship between regional TEC values obtained after the evaluation and global TEC values. There is a positive and quite high correlation between the regional (RIM) TEC values produced by the calculated correlation coefficients and the global (CODE, ESA, JPL) TEC and IRI TEC values.Öğe Importance of probability levels for robustness analysis of geodetic networks(TAYLOR & FRANCIS LTD, 2014) Yetkin, M.; Berber, M.; Inal, C.Robustness Analysis is a natural merger of reliability and strain and defined as the ability to resist deformations caused by the maximum undetectable errors. Internal reliability criterion describes maximum undetectable errors in observations, which would not be detected by Baarda's statistical testing method (data snooping) based on the chosen Type I and II error probabilities. The non-centrality parameter is a function of probability levels and it plays an important role in Robustness Analysis. In this paper, it is aimed to show the impact of non-centrality parameter on the displacements and the relationship between the selected confidence level for confidence regions and threshold values in a geodetic network. For a geodetic network example, a GPS network is chosen and computations of displacements and threshold values (derived from confidence regions) have been carried out for both in-context and out-of context approaches. According to our results, the non-centrality parameter controls the magnitudes of displacements without affecting their relative behaviours. Statistically, lower probability levels are desired. However, if error probabilities are decreased, the non-centrality parameter increases. Since, the non-centrality parameter scales the displacements, a balance between both types of decision error is needed to obtain displacement values that are smaller than threshold values in order to reach a totally robust network at the required level of probability.Öğe L-1 NORM MINIMIZATION IN GPS NETWORKS(MANEY PUBLISHING, 2011) Yetkin, M.; Inal, C.The least squares method is a statistical tool for the estimation of unknown parameters. All the results which are derived from the method of least squares are deteriorated when outliers are present in the observation data. Therefore, outliers have to be detected and eliminated by using statistical tests or robust methods. For this purpose, L-1 norm minimization, which is a robust method, can be used in geodetic networks. In this paper, the formulation of L-1 norm minimization for correlated observations is presented. The method is applied to a simulated GPS network. The performances of the least squares method and L-1 norm minimization are compared in the cases of observations with or without outliers. Our example shows that L-1 norm minimization is a more successful method than the least squares method for outlier detection and the obtained coordinates are more reasonable and reliable than those from the least squares when some observations are burdened with blunders.Öğe THE OPTIMAL DESIGN OF BASELINE CONFIGURATION IN GPS NETWORKS BY USING THE PARTICLE SWARM OPTIMISATION ALGORITHM(TAYLOR & FRANCIS LTD, 2011) Yetkin, M.; Inal, C.; Yigit, C. O.The selection of the optimal GPS baselines can be performed by solving the geodetic second-order design (SOD) problem. In this paper, the particle swarm optimisation (PSO) algorithm, a stochastic global optimisation method, has been employed for the selection of the optimal GPS baselines to be measured in the field that will meet the postulated criterion matrix at a reasonable cost. PSO, which is an iterative-heuristic search algorithm in swarm intelligence, emulates collective behavior of bird flocking, fish schooling or bee swarming, to converge to the global optimum. The fundamentals of the algorithm are given. Then, the efficiency and the applicability of the algorithm are demonstrated with an example of GPS network. Our example shows that the PSO is practical because it does not produce negative or greater than maximum achievable weights of available instruments; it is effective because it yields networks that meet the optimisation criteria; and it is reliable because it converges to the global optimum of an objective function. It is also suitable for non-linear matrix functions that very often encountered in geodetic network optimisation.Öğe Optimal Design of Deformation Monitoring Networks Using the Global Optimization Methods(SPRINGER, 2015) Yetkin, M.; Inal, C.Geodetic networks are very important tools that can be used to monitor crustal movements or the deformation of structures. However, a geodetic network must be designed to sufficiently meet some network quality requirements such as accuracy, reliability, sensitivity and economy. This is the subject of geodetic network optimization. Traditional methods have been used for solving geodetic optimization problems. On the other hand, some evolutionary algorithms such as the particle swarm optimization algorithm have been started to be recently used. These methods are inspired by optimization and adaptation processes that are encountered in the nature. They are iterative procedures for quickly and efficiently solving complex optimization problems. They may provide global optimum solution or at least near-optimum solutions to problems. In this paper, the use of the shuffled frog-leaping algorithm for the optimal design of a deformation monitoring network is studied. The aim is to design and optimize a geodetic network in terms of high reliability.Öğe Scaling of EDM calibration baselines by GPS and controlling of EDM parameters(COMMONWEALTH ASSOC SURVEYING LAND ECONOMY, C A S L E, 2008) Inal, C.; Sanlioglu, I.; Yigit, C. O.The calibration values of electromagnetic distance measurements, which have been given by their own firms, can lose their currency in time. So, the EDMs must be controlled in the particular time intervals. The EDM controls have been usually made in the EDM calibration baselines, which are constituted for this aim. Zero addition, scale coefficient and phase difference measurement function constitute the measurement function as a result of control done. The EDM calibration baseline must be scaled to determine the scale coefficient. Not only high accuracy instruments as Kern Mekometer 3000 but also GPS can be used for scaling. In this study, it has been investigated that possibility of scaling of EDM calibration baseline by using GPS and the scaled EDM calibration baseline, and the calibration parameters of Sokkisha SET2, Topcon GTS701, Topcon GTS 229 and Sokkia Power SET 2000 electronic tacheometers have also been estimated.
