Engin Gülal

GPS Velocity and Strain Rate Fields in Southwest Anatolia from Repeated GPS Measurements

Southwestern Turkey is a tectonically active area. To determine kinematics and strain distribution in this region, a GPS network of sixteen stations was established. We have used GPS velocity field data for southwest Anatolia from continuous measurements covering the period 2003 to 2006 to estimate current crustal deformation of this tectonically active region. GPS data were processed using GAMIT/GLOBK software and velocity and strain rate fields were estimated in the study area. The measurements showed velocities of 15–30 mm/yr toward the southwest and strain values up to 0.28–8.23×10−8. Results showed that extension has been determined in the Burdur-Isparta region. In this study, all of strain data reveal an extensional neotectonic regime through the northeast edge of the Isparta Angle despite the previously reported compressional neotectonic regime. Meanwhile, results showed some small differences relatively with the 2006 model of Reilinger et al. As a result, active tectonic movements, in agreement with earthquake fault plane solutions showed important activity.

Multisensor Railway Track Geometry Surveying System

Linear variable differential transformers (LVDTs) and inclinometers are widely used in many industrial establishments, particularly in the metrology area. These sensors are used by many engineering disciplines because of their high-precision characteristics. In addition, Global Navigation Satellite System (GNSS) receivers and total stations are widely used in geodesy. Using GNSS receivers is very popular, particularly for navigational purposes. In this paper, a new railway track geometry surveying system, which is designed by integrating the LVDT, inclinometer, GNSS receiver, and total station, is introduced. This new surveying system is an alternative to classical geodetic measurement methods that are often used for controlling the railway track geometry. Track gauge, super-elevation, gradient, and track axis coordinates, which are railway geometrical parameters, can be instantly determined while making measurements by using the new surveying system.

Ambient Vibration Measurements of the Bosphorus Suspension Bridge by Total Station and GPS

Traffic and wind excitations have been used to obtain the dynamic characteristics of the Bosphorus Suspension Bridge in Istanbul, Turkey. Ambient vibration measurements (AVMs) on the bridge deck were obtained using the Total Station (TS) in 2003 and the Global Positioning System (GPS) in 2005. Frequencies can be effectively estimated from AVMs using the peak-peaking (PP) method in the frequency domain. For the main span, seven vertical and seven lateral frequencies were obtained from TS measurements. From the GPS measurements, 13 vertical and 9 lateral frequencies were obtained. All 36 frequencies were in the range 0–1.5 Hz. Estimated frequencies from the measurements and three-dimensional finite-element (FE) models were compared. In general, the agreement among frequencies was good. Comparison with frequencies from more limited studies undertaken in 1973, 2003, and 2005 showed that there was no unexpected behaviour in the movements of the bridge and the bridge continues to behave in accordance with the original design specifications.

ANALYSIS AND MANAGEMENT OF GNSS REFERENCE STATION DATA

E. Gulal i dr. Analiza i upravljanje GNSS podacima referentne postaje Tehnicki vjesnik 22, 2(2015), 407-414 407 ISSN 1330-3651 (Print), ISSN 1848-6339 (Online) DOI: 10.17559/TV-20140717125413

Structural deformations analysis by means of Kalman-filtering

The surveillance of engineering structures like dams is an interdisciplinary task and mainly focused on the assessment of stability and reliability of the objects to be monitored. To show the co-operation of the disciplines involved in a comprehensible manner, it is suitable to use system analysis approaches. Structural deformations analysis by means of system analysis is explained in the following with an example of a dam. The determination of the dam deformations is demonstrated by an integration of computed and measured data by using Kalman Filtering.

Monitoring the tectonic plate movements in Turkey based on the national continuous GNSS network

In recent decades, the space geodesy has been applied to the areas such as transportation, infrastructure planning, navigation, etc. Among them, the precise positioning at the Global Navigation Satellite System (GNSS) stations yields better view in the understanding of the crustal deformation that requires global-scale measurements. There have been numerous studies examining the data process of continuous GNSS observations in the field of earth monitoring. More recently, GNSS stations established for continuously operating reference station networks have been beneficial resources in the tectonic plate-monitoring studies in lieu of campaign-type observations. However, this requires that the Continuously Operating Reference Station (CORS) should be established on stable structures acting like foundations and requires investigation of the long-term repeatability time series. This study aims to introduce recently established national CORS network, named CORS-TR, covering the entire Turkey and Northern Cyprus, and to explain the process of the long-term data obtained from the network on the characteristics of the tectonic plate movement within the area. The results of the CORS-TR data process present a great potential of using continuously operating reference stations not only in real-time kinematic applications of conventional geodesy studies but also in detecting and monitoring the crustal deformations of those that are crucial in earthquake-prone areas like Turkey. Since the findings are computed from the results of the all permanent stations of CORS-TR network, this study also examines the GNSS observation quality of the network for the given time interval. One of the major conclusions of the data process conducted in the study displays that the CORS-TR stations established on the carefully selected large and low-rise existing building had been more stable than the stations on the ground which have been subjected to soil settlement since the construction.

Determining the behaviour of high-rise structures with geodetic hybrid sensors

Observing the normal oscillations and the behaviours of high-engineering structures has become almost a necessity in terms of construction security and human health. For this purpose, an real-time kinematic GPS (NovAtel 400) and a tilt sensor (Leica Nivel20) were installed in a TV tower (220 m high) located in Istanbul, Turkey. The observation serials were recorded over a period of 9 days. All data-sets in X and Y directions were examined in the time domain and were analyzed using FFT€. The dominant frequency values (significant frequencies) were determined by comparing at the high- and low-frequency values. These dominant frequencies showed that the tower made 4- and 6-second short-period oscillations and 24- and 12-hour long-period oscillations. All the observation signals were re-created by the significant low-frequency values using the inverse Fourier transform. Thus, the motion model of the tower was determined over 9 days. In this study, the 24-hour and 12-hour periodic oscillations were defined that represent the behaviour of the tower in relation to the effect of the suns radiation and the temperature changes.

Wireless 3-axis accelerometer system for measurement of structural displacement

In this study, we present the design of a 3-axis acceleration measurement system that is capable of UTC (Coordinated Universal Time) time-stamping captured from a Global Positioning System (GPS) receiver module. With this achievement, the system is able to monitor and record the 3-axis vibrations with respect to an absolute time rather than the local sensor (and computer) time. Acquired 3-axis acceleration data and UTC are transferred via Bluetooth® protocol and developed software which enables monitoring and recording of UTC and acceleration data on a PC, respectively. For verification and synchronization quality test of acceleration data, shake-table tests were conducted for simulation of structural displacement and the calculated displacements were compared with a displacement sensor of a commercially available shake table system.

An investigation of different Wi-Fi signal behaviours and their effects on indoor positioning accuracy

In recent years, in addition to 2.4 GHz Wi-Fi signals, 5 GHz signals have been introduced making it possible to transmit data at both IEEE 802.11n and 802.11ac standards. Therefore, researchers have increasingly focused on developing indoor positioning applications based on Wi-Fi dual band. This study was conducted in two stages. In the first stage, we investigated the behaviours of 2.4 and 5 GHz Wi-Fi signals by collecting received signal strength (RSS) values from access points and determined the relationship between RSS and distance for each signal frequency using a curve fitting technique. Furthermore, we comparatively analysed signal fluctuations and their effects on positioning accuracy. In the second part of the study, we compared the positioning accuracy of four algorithms; namely, bilateration, trilateration, weighted iterative non-linear least square and extended Kalman filter using 2.4 and 5 GHz Wi-Fi signals. The experimental results revealed that the 5 GHz signals were more stable and had better positioning accuracy than the 2.4 GHz signals. Concerning the positioning algorithms, bilateration had the best positioning accuracy at both frequencies.

Crustal Deformation Modelling by GNSS Measurements: Southwestern Anatolia, Turkey

The Western and Southwestern Anatolia are located in a tectonically active region in Turkey (Fig. 1). Many studies have been conducted on the mechanism of fault systems of this region. Open image in new window Fig. 1 Major tectonic structures of the Southwestern Anatolia