Reha Metin Alkan

GPS, GALILEO and GLONASS satellite navigation systems & GPS modernization

Satellite navigation technology is rapidly evolving. The modernisations in GPS, full deployments of GLONASS and GALILEO after 2008 will facilitate the development of new applications, hence opening new markets. It is time to prepare for this new commodity: ubiquitous provision of reliable and accurate positioning and timing services has already started to transform our societies. This paper will give an overview of satellite navigation systems, GPS, GLONASS and GALILEO as well as GPS modernisation which has been carried out fur a few years.

Usability of the GPS Precise Point Positioning Technique in Marine Applications

This study investigates the accuracy of an online Precise Point Positioning (PPP) service operated by the Geodetic Survey Division of Natural Resources Canada (NRCan), Canadian Spatial Reference System (CSRS)-PPP, by using single/dual-frequency Global Positioning System (GPS) data collected by dual-frequency geodetic-grade and Original Equipment Manufacturer (OEM) board type single-frequency GPS receivers. In this work, a kinematic test was carried out in Halic Bay (Golden Horn), Istanbul, Turkey, to assess the performance of the PPP method in a dynamic environment. Based on this study, it can be concluded that the coordinates estimated from the online CSRS-PPP service have a potential of about metre-level accuracy by processing single frequency data collected by an OEM receiver and about a decimetre to a few centimetres level accuracy by processing dual frequency data collected by a geodetic-grade receiver. In general, results show that the PPP technique has become a significant alternative to the conventional relative (differential) positioning techniques (i.e., Differential GPS (DGPS), Real-time Kinematic (RTK) ). The technique does not suffer from the drawbacks of the DGPS technique and has potential to provide the same position accuracy without the requirement for a reference station. Consequently, it has been concluded that the PPP technique may be effectively used in marine applications due to its ease of use and provision of high accuracy, as well as being able to offer reduced field operational costs.

A Performance Analysis of Low-Cost GPS Receivers in Kinematic Applications

Low-cost OEM GPS receivers with the capability of tracking the carrier phase are now used for many applications in the navigation and tracking arena. These receivers provide flexibility in applying carrier smoothing algorithms to improve the pseudorange positioning accuracy and even perform carrier-phase differential positioning. In this study, the performance of a low-cost single-frequency OEM GPS receiver for high-accuracy kinematic positioning in marine applications is investigated. As a first step, a set of zero baseline tests were carried out to evaluate the performance of the GPS receivers. In the second stage, a kinematic test was conducted at the Halic (Golden Horn), Istanbul. The results show that kinematic positioning with centimetre level accuracy can be achieved by the low-cost OEM GPS receiver in differential mode, suggesting its use in a variety of kinematic applications. The use of such a system could considerably reduce the cost of the GPS receiver and the total project costs of many applications.

Bibliometric analysis on global Behçet disease publications during 1980–2014: is there a Silk Road in the literature?

Behçet disease (BD) is a chronic and multisystemic vasculitis characterized with recurrent oral and genital ulcers, uveitis, arthritis and skin manifestations. The highest prevalence of the disease has been reported in regions historically involved in the Silk Road routes.

Survey Boat Attitude Determination with GPS/IMU Systems

Any vehicle such as a vessel or aeroplane has three attitude parameters. These are most commonly defined as pitch, roll and heading from true north. In hydrographic surveying, determination of these parameters is essential for the correction of multi-beam echo sounder measurements. In the study on which this paper is based, two of the three parameters, the pitch and roll angles, were measured with an inexpensive IMU (Inertial Measurement Unit) device. The third was calculated from GPS carrier phase measurements that were collected from two antennas on the boat. The GPS antennas depart from the vertical when they are subject to pitch and roll effects. In this case, the coordinates derived from GPS will be erroneous. Thus, if heading is to be calculated accurately, the horizontal coordinates have to be corrected for pitch and roll. This paper defines an algorithm for the purpose that enables pitch and roll angles to be measured with an accuracy of about 0.110 arcdeg and headings computed with an accuracy of about 0010 arcdeg.

Sub-Metre Accuracy for Stand Alone GPS Positioning in Hydrographic Surveying

The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metres with SA switched off; this is not adequate for most hydrographic studies. This study aims to improve this level of accuracy using a single geodetic receiver in stand-alone mode by applying a phase smoothing algorithm. The algorithm described in this study requires that the measurements be started from a known point for initialisation. The test site selected for the study is Halic bay, Istanbul. After GPS data were collected on a geodetic point for initialisation, the receiver was moved to a hydrographic vessel and trial measurements were performed along several survey profiles. The position of the vessel was calculated at every epoch using the carrier phase smoothing algorithm. In order to analyse the accuracy of the results, a second receiver collected data on another known point on the seashore during the whole session. The position of the vessel was accurately determined using a kinematic positioning method considering the data collected by both receivers. The results produced show that an accuracy of less than a metre can be achieved using the approach considered in this study.

Monitoring the deformation and strain analysis on the Ataturk Dam, Turkey

ABSTRACT Every man-made structure creates certain risks — dams are no exception. Most failures in man-made structures that have occurred could have been avoided if the structures’ behaviour had been inspected, monitored, and analyzed continuously, and if proper corrective measures had been taken in a timely fashion. The DSI (The General Directorate of State Hydraulic Works), which is the institution responsible for dam safety, has long used surveying methods to measure the displacements of geodetic points as a part of dam monitoring policy. In this study, we focus on the dams mechanical behaviour throughout a time period of more than 10 years. These study results have been derived from a separate, ongoing project that has monitored deformation on the Ataturk Dam and is now determining the water level of the reservoir. The project results show that although the dam body has become more stable and the water load behind the dam has increased, the rate of displacement of the dam has declined significantly. From these results, it can be seen that the reservoir water level can be increased evenly over time and that 542 m is the maximum water level of the dams reservoir.

Decimeter-level positioning in dynamic applications with a single GPS receiver

Although the ongoing GPS modernization studies provide better autonomous positioning accuracy (i.e. a few meters), this accuracy level is not enough for many surveying applications. Depending on the developments in satellite-based positioning technology and GNSS data availability and analysis techniques, some new approaches and algorithms have been proposed in the world of global positioning to enhance the autonomous positioning accuracy. In this study, a precise positioning technique, named “self-differential method”, is introduced using the dual frequency GPS data collected by a single geodetic-grade GPS receiver. The technique uses iono-free carrier phase observations, precise satellite ephemerides and satellite clock data. In order to validate the performance of the introduced method in a dynamic environment two kinematic tests were conducted at Haliç Bay in Istanbul, Turkey. The results show that the method is capable of achieving decimeter level of positioning accuracy without the need of an additional reference station or any other data while reducing the field operational costs.

REDUCTION OF HEAVE, PITCH AND ROLL EFFECTS IN HYDROGRAPHIC SURVEYING

Abstract A hydrographic survey vessels show three-dimensional movements due to environmental effects, such as wind, current, other vessel wakes, etc. As a result of this, the vessel will experience Pitch, Roll and heave. These motions (if ignored) cause errors in depth and in the positioning of the sounding. The magnitude of the errors can reach up to even meters depending on the marine environment conditions, vessel size, vessel characteristics, and especially wave height. However, accurate and reliable depth and position data are needed in bathymetric charts prepared for shallow water navigation, dredging, various engineering applications, harbour manoeuvres, and maximizing cargo capacity safely. Therefore, compensation of vessel motion is necessary for several applications. The goal of this study is to determine and reduce the heave, Pitch and Roll effects in hydrographic surveying realized by a single narrow beam system. As a result of this study, heave, Pitch and Roll corrections are calculated and applied to the relevant data.

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.