Ayhan Ceylan

Performance evaluation of short to long term GPS, GLONASS and GPS/GLONASS post-processed PPP

Abstract In recent years, in addition to the GPS constellation, the ability to utilise extra satellites available in the GLONASS system enhanced the capabilities and possible applications of precise point positioning (PPP) method. However, the intrinsic differences between GPS and GLONASS and the lack of a fully tested global tracking network of multi-GNSS systems necessitate the evaluation of their combined use. This paper offers a comprehensive statistical assessment of static PPP using GPS-only, GLONASS-only and GPS/GLONASS combined data. Data analysis is performed in a short (hourly to daily) and a long (several weeks) term, spanning observations from eleven IGS stations. Evaluation of the results reveals insignificant differences in the accuracy and repeatability among the three satellite constellation solutions for long (8 h, 24 h) observation times. The superiority of the combined GPS/GLONASS solution is apparent for short (1 h, 2 h) observation periods, whereas analysis confirms the stability of PPP solutions for the very long (several weeks) observation periods irrespectively of the satellite constellation used.

Displacement response of a concrete arch dam to seasonal temperature fluctuations and reservoir level rise during the first filling period: evidence from geodetic data

The present study evaluates the dynamic behaviour of the Ermenek Dam, the second highest dam in Turkey, based on conventional geodetic measurements and Finite Element Model (FEM) analyses during its first filling period. In total, eight periods of measured deformation are considered from the end of construction until the reservoir reached its full capacity. The displacement response of the dam to the reservoir level and to seasonal temperature variations is examined in detail. Time series of apparent total displacements at the middle of the crest of the dam exhibits periodicity and linear trends. Correlation analysis revealed that periodic and linear displacement responses of the dam are related to variations of seasonal temperature and linearly increased reservoir level, respectively, indicating a relation between temperature, water load and dam deformation. It is also concluded that measured deformations based on geodetic data show good agreement with the predicted deformation obtained by the FEM analysis.

PHOTOGRAMMETRIC APPROACH IN DETERMINING BEAM-COLUMN CONNECTION DEFORMATIONS

In accordance with the advances in technology, displacement calculation techniques are ever developing. Photogrammetry has become preferable in some new disciplines with the advances in the image processing methods. In this study, the authors have used two different measurement techniques to determine the angles of rotation in beam-column connections that are subjected to reversible cyclic loading. The first of these is the method that is widely used, the conventional method in structural mechanics experiments, where Linear Variable Differential Transformers (LVDTs) are utilized; and the second is the photogrammetric measurement technique. The rotation angles were determined using these techniques in a total of ten steel beam-column connection experiments. After discussing the test procedures of the aforementioned methods, the results were presented. It was observed that the rotation angles measured by each method were very close to each other. It was concluded that the photogrammetric measurement technique could be used as an alternative to conventional methods, where electronic LVDTs are used.

Precise height determination using simultaneous-reciprocal trigonometric levelling

Abstract Precise levelling method has been used for the determination of precise height for many years. The application of this technique is difficult, time consuming and expensive especially in rough terrains. These difficulties have forced researchers to examine alternative methods of height determination. As a result of modern technological developments for high-tech instruments, research of the precision trigonometric levelling has been required once again. In this study, simultaneous-reciprocal trigonometric levelling (SRTL) method is applied with different sight distances in order to determine optimum sight distances using a sample test network in Selcuk University Campus, Konya, Turkey. The results are compared with precise geometric levelling in terms of precision, cost and feasibility. SRTL method for sight distance S=200m resulted with the standard deviations of ±1.86 mm / √ km and with the production speed of 4 km/day.