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    Comparison of L-1 Norm and L-2 Norm Minimisation Methods in Trigonometric Levelling Networks
    (UNIV OSIJEK, TECH FAC, 2018) Inal, Cevat; Yetkin, Mevlut; Bulbul, Sercan; Bilgen, Burhaneddin
    The most widely-used parameter estimation method today is the L-2 norm minimisation method known as the Least Squares Method (LSM). The solution to the L-2 norm minimisation method is always unique and is easily computed. This method distributes errors and is sensitive to outlying measurements. Therefore, a robust technique known as the Least Absolute Values Method (LAVM) might be used for the detection of outliers and for the estimation of parameters. In this paper, the formulation of the L-1 norm minimisation method will be explained and the success of the method in the detection of gross errors will be investigated in a trigonometric levelling network.
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    Determination of 2011 Van/Turkey earthquake (M = 7.2) effects from measurements of CORS-TR network
    (TAYLOR & FRANCIS LTD, 2014) Yildirim, Omer; Yaprak, Servet; Inal, Cevat
    Turkey is a country that has active fault lines and is prone to earthquake. The positional variations resulted from the Van earthquake (a magnitude of M = 7.2) on 23 October 2011 and were calculated by using data from CORS-TR (Continuously Operating Reference Station network) stations. The GPS data from the CORS-TR stations effected from the earthquake were evaluated by the BERNESE 5.0 software. For calculating the positional displacements in the CORS-TR stations after the earthquake that occurred in Van, the measurements from 16 International GNSS Service (IGS) stations around Turkey, where their coordinates and velocity vectors were considered to be constant at the ITRF2005 datum. The greatest variation was measured from the Muradiye station, which is the closest point to the epicentre of the earthquake. The variation in this station was -42.7mm in the vertical direction, -60.3mm in the northern direction and -18.7mm in the eastern direction.
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    DETERMINING REGIONAL IONOSPHERIC MODEL AND COMPARING WITH GLOBAL MODELS
    (ASSOC SURVEYORS SLOVENIA, 2017) Basciftci, Fuat; Inal, Cevat; Yildirim, Omer; Bulbul, Sercan
    GNSS (Global Navigation Satellite System) signals pass through various layers of the atmosphere until reaching the receiver on the Earth. The ionosphere, one of these layers, is about 70 km to 1000 km above the Earth surface and constantly changes with the time of day, seasons, geographical location and solar explosions. The GNSS signals affected by the variable structure of the ionosphere are proportional to the total electron content (TEC). Determination of the TEC change is important for modelling of the ionosphere. In this study, totally 26 stations, including 14 TUSAGA-ACTIVE (CORS-TR) stations in Turkey and 12 IGS stations, were selected and evaluated. Bernese v5.2 GNSS software was used for evaluation. TEC values were calculated at intervals of two hours, one day per each month, from 2009 to 2015. TEC values, obtained from GNSS measurements using Single Layer Model, were compared with global ionosphere maps (GIM-TEC) issued by the Center for Orbit Determination in Europe (CODE), the European Space Agency (ESA), the Jet Propulsion Laboratory (JPL), and TEC (IRI-2012 TEC) values obtained from international ionosphere reference program. The best approach to regional ionosphere model obtained as result of comparison was shown by CODE and ESA. Additionally TEC map was produced for the selected area as utilizing regional and global TEC values.
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    ROBUSTNESS ANALYSIS OF GEODETIC NETWORKS IN THE CASE OF CORRELATED OBSERVATIONS
    (UNIV FEDERAL PARANA, CENTRO POLITECNICO, 2013) Yetkin, Mevlut; Berber, Mustafa; Inal, Cevat
    GPS (or GNSS) networks are invaluable tools for monitoring natural hazards such as earthquakes. However, blunders in GPS observations may be mistakenly interpreted as deformation. Therefore, robust networks are needed in deformation monitoring using GPS networks. Robustness analysis is a natural merger of reliability and strain and defined as the ability to resist deformations caused by the maximum undetectable errors as determined from internal reliability analysis. However, to obtain rigorously correct results; the correlations among the observations must be considered while computing maximum undetectable errors. Therefore, we propose to use the normalized reliability numbers instead of redundancy numbers (Baarda's approach) in robustness analysis of a GPS network. A simple mathematical relation showing the ratio between uncorrelated and correlated cases for maximum undetectable error is derived. The same ratio is also valid for the displacements. Numerical results show that if correlations among observations are ignored, dramatically different displacements can be obtained depending on the size of multiple correlation coefficients. Furthermore, when normalized reliability numbers are small, displacements get large, i.e., observations with low reliability numbers cause bigger displacements compared to observations with high reliability numbers.
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    Statistical analysis of accuracy and precision of GNSS receivers used in network RTK
    (SPRINGER HEIDELBERG, 2018) Inal, Cevat; Bulbul, Sercan; Bilgen, Burhaneddin
    It is important to make accurate and precise measurements in surveying applications. The concepts of accuracy and precision are not synonymous, even though they are commonly used in place of each other. Nowadays, real-time kinematic (RTK) method is widely used at surveying. As the RTK method can be done depending on a reference station, in countries which establish Continuously Operating Reference Stations (CORS) Network, method known as Network-RTK (N-RTK) can be done depending on the CORS Network. Continuously Operating Reference Stations-Turkey Network (CORS-TR), which consists of 146 reference stations that allow positioning both real time and post-process, was established in 2009. In this study, accuracy and precision of Global Navigation Satellite Systems (GNSS) receivers are tried to determine depending on different correction techniques. For this purpose, 12-h GNSS observations were performed at SLCK-Turkish National Fundamental GPS Network (SLCK-TNFGN) point. The observations were adjusted based on CORS-TR. N-RTK measurements were performed with different GNSS receivers, and accuracies of the receivers were investigated. In order to determine precisions of the receivers, means of RTK measurements were calculated and precisions of the receivers were determined. As a result of investigation, it is seen that accuracy and precision of receivers at 2D positioning and height vary depending on correction technique.
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    SURVEYING AND MAPPING USING MOBILE PHONE IN ARCHAEOLOGICAL SETTLEMENTS
    (CLUJ UNIV PRESS, 2017) Inal, Cevat; Kocak, Ozdemir; Esen, Omur; Bulbul, Sercan; Kizgut, Rahim
    Depending on the development of technology, the boundary concept between different disciplines became unclear today and it became necessary to work jointly depending on data sharing. Also Producing the maps is effected the development of the technology and positioning of desired area is become very fast. Today, instead of hand GPS, users can be obtained coordinate desired via programs which are compatible with mobile phone. CORS (Continuously Operation Reference System) GNSS (Global Navigation Satellite System) receivers which measure points coordinates (x, y, h) at all weather conditions, day and night will become compatible Mobil PC devices (Mobil Phone) via compatible software. By means of this study, including the surveys of Ancient History and Archaeology sciences, different samples belonging to different periods have been evaluated. In this study, coordinates obtained with CORS-TR (Continuously Operation Reference System-TuRkey) and Asus Zenfone 6 in which Kocaman Pro Software was used at selected areas compare with each and the usage of Asus Zenfone 6 was investigated in term of easiness and accuracy in Archaeological Settlements. This study was carried out at the Hatip Castle, Malas II and Campus ruins in Konya. Only horizontal accuracy (x, y) was investigated. The horizontal accuracy is higher in Malas II and Campus ruins than Hatip Castle. This is due to the distance of the GSM networks to the application area.