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    Comparison of accuracy of GPS techniques
    (ELSEVIER SCI LTD, 2012) Berber, Mustafa; Ustun, Aydin; Yetkin, Mevlut
    Accuracies of relative positioning techniques namely rapid static, pseudo-kinematic, kinematic, and real-time kinematic are investigated to determine their performances against static survey technique that yields the most precise results. Measurements are taken at seven National Geodetic Survey points along Road 714 in Florida using three sets of triple frequency Global Navigation Satellite System receivers. The data are processed using the software provided by the manufacturer. It turns out that pseudo-kinematic technique produces the closets results to static survey results. (C) 2012 Elsevier Ltd. All rights reserved.
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    Comparison of the KTH and remove-compute-restore techniques to geoid modelling in a mountainous area
    (PERGAMON-ELSEVIER SCIENCE LTD, 2012) Abbak, Ramazan Alpay; Erol, Bihter; Ustun, Aydin
    In mountainous regions, a gravimetric geoid determination is a difficult task which needs special attention to obtain reliable results satisfying the demands, e.g. of the engineering infrastructure. The present study compares the KTH (Royal Institute of Technology) method with the remove-compute-restore (RCR) technique to attain a precise geoid model for the Konya Closed Basin (KCB) and thus aims to clarify the theoretical and numerical differences between these techniques. The KCB located in the central part of Turkey is a mountainous area with a very limited amount of the ground gravity data. Various data sources, such as the Turkish Digital Elevation Model with 3 '' x 3 '' resolution (TRDEM3), a recently published satellite-only global geopotential model and terrestrial gravity observations are combined in the gravimetric geoid models of the KCB by applying the KTH and RCR techniques, separately. The both gravimetric geoid models (KG-KTH11 and KG-RCR11) are compared with GNSS/levelling data at the control points in the target area, resulting the RMS (Root Mean Square Error) differences of +/- 6.7 cm and +/- 9.8 cm in the absolute sense, respectively. These results show that the KTH method gives more reasonable accuracy than the RCR technique in a mountainous area with scarce terrestrial gravity data. (C) 2012 Elsevier Ltd. All rights reserved.
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    GEOGRAPHIC INFORMATION SYSTEM FOR KONYA CLOSED BASIN PROJECT
    (BULGARIAN CARTOGRAPHIC ASSOC, 2012) Ustun, Aydin; Bildirici, I. Oztug; Ustuntas, Taner; Tusat, Ekrem; Ozkan, Ihsan; Eren, Yasar; Ozdemir, Adnan
    The main goal of the Konya Closed Basin Project is to investigate land subsidence within the basin. The vertical changes have been investigated through GPS measurements and InSAR images taken at different dates. In order to decide whether the land subsidence is significant for land use in residential and agricultural areas within the basin, a GIS system is necessary. For this purpose GoogleEarth, MapInfo and Generic Mapping Tools (GMT) were chosen as GIS software packages. At first, a preliminary study has been performed using I: 100 000 and 1: 250 000 topographic maps which are scanned and registered. A continuous mosaic of map sheets created from them is overlaid on the terrain in the Google Earth. GPS deformation network was designed over the mosaic map considering land use and hydrogeological properties of the KCB. Other data that the system contains are GPS points, wells, at which water depth is measured, InSAR images, geologic layers created from geological maps, and land use maps created by using NVDI method. The geology maps are digitized in MapInfo. After the completion of data collection, GIS analyses will be undertaken in order to evaluate land subsidence potential of the basin.
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    Land subsidence in Konya Closed Basin and its spatio-temporal detection by GPS and DInSAR
    (SPRINGER, 2015) Ustun, Aydin; Tusat, Ekrem; Yalvac, Sefa; Ozkan, Ihsan; Eren, Yasar; Ozdemir, Adnan; Bildirici, I. Oztug
    Konya Closed Basin that includes two depression blocks, Konya and Tuz Golu, is the biggest endorheic basin in Turkey. A lowering in the ground levels of the depositional areas has been shown with respect to the surrounding mountains. In the past, this process was controlled by geological and hydrogeological phenomena; nowadays, it has gained a new dimension due to the excessive pumping of groundwater to the Earth's surface. The geodetic techniques such as Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) reveal a considerable land subsidence resulting in the rate of 1-4 cm/year in Konya sub-basin. It seems that the calculated amounts are responsible for changing environmental conditions like seasonality. Both GPS and differential InSAR techniques verify these relatively small fluctuations in the subsidence development. Target districts that should be observed primarily are agricultural zones where groundwater is overused for irrigation and regions where human population density is high. The geocoded interferogram and vegetation index map verify the spatial relation between the subsidence and green areas. In this study, a project dealing with the investigation of the land subsidence occurrences and of their possible causes and consequences within a specific part of Konya Closed Basin is introduced.
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    Multipath interference cancelation in GPS time series under changing physical conditions by means of adaptive filtering
    (SPRINGER HEIDELBERG, 2018) Ustun, Aydin; Yalvac, Sefa
    Multipath, a highly autocorrelated signal is observable phenomena during time periods longer than the sidereal period of Global Positioning System (GPS) satellites in their constellations. Multipath pattern and sidereal repeat time interaction are examined in terms of time series correlations of topocentric coordinates using GPS code and phase observations collected at high and low frequencies. The horizontal and vertical components at 5 and 30 s sampling rates are analyzed to detect and remove multipath classified by their M P (1) levels and baseline lengths. For the selected 11 stations that have 24-hour data from CORS stations in the USA and Turkey, the repeat times of the GPS constellation were identified as a function of maximum cross-correlation of adjacent time series. The multipath interference signal from two-day time series data is removed by an adaptive filter to improve time series of coordinate estimates. After the filtering process, an effective epoch based position tracking has been accomplished, especially in the height component. The position errors disappeared to maximum possible extent in the pseudo-range measurements. Up to 70% improvement for the phase derived coordinates in reflective environment has been achieved over the baselines ranging from 1 km to 175 km. For the phase observables, the filter success directly related to the multipath level which is specific to the station.
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    A software package for computing a regional gravimetric geoid model by the KTH method
    (SPRINGER HEIDELBERG, 2015) Abbak, Ramazan Alpay; Ustun, Aydin
    Nowadays, the geodetic community has aimed to determine 1-cm accuracy gravimetric geoid model, which satisfies the demands of most engineering applications. However, the gravimetric geoid determination is a difficult mission which needs an exclusive attention to obtain reliable results for this purpose. Today, Least-Squares Modification of Stokes (LSMS) formula which is so-called the KTH method (Swedish Royal Institute of Technology) has been performed in the regional geoid studies. Based upon the earlier investigations, the KTH method provides more reasonable results than the Remove Compute Restore technique, especially in roughly terrain with sparse terrestrial gravity data. Nevertheless, a compact and practical software package is now not available for users and researchers in geosciences. Thus, in this paper, a scientific software called "LSMSSOFT" is developed and presented by adding a new algorithm which speeds up the evaluation of Stokes' integral. Afterwards, the LSMSSOFT is applied to a case study for the construction of a geoid model over the Auvergne test area in France. Consequently, the algorithm treated in the software and its results imply that the LSMSSOFT is an alternative software package for modelling the gravimetric geoid by the KTH method.