In this study, detectability of high-frequency structural vibrations based on only one GNSS recei... more In this study, detectability of high-frequency structural vibrations based on only one GNSS receiver and developed kinematic model solution was investigated. For this purpose, two data sets generated from dual frequency GNSS receiver attached on flexible steel bar(rod) which oscillates one way direction were used. Free decayed sinusoidal oscillation experiments were performed to produce both the first mode and the second mode frequency together. GNSS observations were processed by both the developed kinematic model algorithm and PPP (Precise Point Positioning) method in kinematic mode. Structural vibrations of the rod in time and frequency obtained by both methods were compared. The results have demonstrated that the developed kinematic algorithm can determine high-frequency structural vibrations as much as PPP method. Keywords : Single point kinematic solution, Kinematic-PPP, GPS.
Abstract Since the 1990s, seismic deformations have been commonly determined using the Global Nav... more Abstract Since the 1990s, seismic deformations have been commonly determined using the Global Navigation Satellite System (GNSS). Recently, the GNSS systems have become even more powerful with the use of new technologies in innovative studies. In this study, the GNSS data was used to investigate interseismic, coseismic and postseismic deformation and velocity of the Gokceada-Samothraki earthquake (Mw = 6.9) that occurred on May 24, 2014. The data was obtained at 30 s (0.033 Hz) and 1 s (1 Hz) intervals from the GNSS receivers in the network of Continuously Operating Reference Stations, Turkey (CORS-TR). For the interseismic period, the daily coordinate time series of 12 stations located within 90–250 km of the earthquake epicenter was evaluated for the displacement of stations over a period of approximately 2000 days prior to the day of the earthquakes, from October 1, 2008 to May 23, 2014. In order to analyze the ground motion displacement during the Gokceada-Samothraki earthquake, 1 Hz data from 8 continuous GNSS stations was processed using precise point positioning (PPP) and relative positioning methods to estimate the epoch-by-epoch positions of the stations. During the earthquake, coseismic displacements of approximately 7 and 30 mm were detected in the NW direction at the YENC and CANA stations, respectively. However, at the IPSA station, a coseismic deformation of 20 mm was observed in the NE direction. There were no significant changes at the other stations during the earthquake. For the postseismic period, the daily coordinate time series of the 12 stations were evaluated for station displacements for 570 days after the day of the earthquakes, from May 24, 2014 to January 1, 2016. The results demonstrated that no significant postseismic deformation with the exception of the EDIR station. An abnormal deformation caused by local factors was determined at the EDIR station. In this study, the PPP and the relative solution were also compared in terms of capturing the earthquake wave motion. The results demonstrated that the PPP-based solutions showed good agreement with those of relative positioning in terms of the ability to capture coseismic displacement.
GNSS technology has been extensively used to measure crustal deformation and widely used to const... more GNSS technology has been extensively used to measure crustal deformation and widely used to construct displacement waveforms. GNSS seismology uses GNSS receiver as displacement seismometer for earthquake studies. In other words, it can sense large dynamic displacement without saturation. In GNSS, relative positioning method requires a reference station with no-motion whereas Precise Point Positioning (PPP) method does not need any reference station. However, PPP method, unlike relative positioning method, requires readily precise GNSS satellite orbit and clock product calculated beforehand to perform absolute positioning using a single GNSS receiver data. In case of large earthquake, it may be crucial to select stable reference for relative positioning. Therefore, in order to monitor ground motion pattern caused by the earthquake, PPP method is advantageous because it provides absolute coseismic displacements with respect to a global reference frame. In this study, we investigate th...
Low-cost OEM GPS receivers with the capability of tracking the carrier phase are now used for man... more 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 proj...
The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metre... more 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 kin...
ABSTRACT In recent years, the usage of the Precise Point Positioning (PPP) has increased due to i... more ABSTRACT In recent years, the usage of the Precise Point Positioning (PPP) has increased due to its ease of use, providing high accuracy as well as reducing the field operational costs by using only a single GNSS receiver. Moreover, it does not require any additional reference station data or CORS-like network data. It is a positioning technique that has been extensively investigated and used in a variety of applications, mainly for conventional surveying applications and time-transfer, ionospheric and tropospheric characterization. In GNSS positioning, limited satellite visibility in obstructed areas and poor satellite geometry adversely affect the accuracy of results. With the revitalization of the GLONASS system reaching to full global coverage, PPP studies have focused on combined GPS and GLONASS solutions. The goal of this study is to investigate the usability of PPP technique in urban areas with GPS-only and GPS + GLONASS data by the use of online-PPP services for sub-decimeter surveying applications. For this purpose, test measurements were conducted in Çorum province of Turkey. Collected data were evaluated with two commonly used PPP services, namely CSRS-PPP operated by the Geodetic Survey Division of Natural Resources Canada (NRCan) and magicGNSS/PPP developed by Spanish GMV Aerospace and Defense Co. Results obtained from this study revealed that for some cases, the use of GLONASS with GPS raises the number of satellites used in the solution twice as much as compared to GPS-only. However, unless satellites geometry gets better, the use of GLONASS has no significant role in strengthening the accuracy of results. The results indicate that an increase in the number of satellites is vital especially in urban areas where minimum number of satellites for a solution may not be obtained. Also, it was observed that when the sufficient numbers of GPS satellites with good geometry are available combining GPS together with GLONASS may not bring any significant contribution to the solution.
The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metre... more 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.
The use of GPS for establishing height control in an area where levelling data are available can ... more The use of GPS for establishing height control in an area where levelling data are available can involve the so-called GPS/levelling technique. Modelling of the GPS/levelling geoid undulations has usually been carried out using polynomial surface fitting, least-squares collocation (LSC) and finite-element methods. Artificial neural networks (ANNs) have recently been used for many investigations, and proven to be effective in solving complex problems represented by noisy and missing data. In this study, a feed-forward ANN structure, learning the characteristics of the training data through the back-propagation algorithm, is employed to model the local GPS/levelling geoid surface. The GPS/levelling geoid undulations for Istanbul, Turkey, were estimated from GPS and precise levelling measurements obtained during a field study in the period 1998–99. The results are compared to those produced by two well-known conventional methods, namely polynomial fitting and LSC, in terms of root mean square error (RMSE) that ranged from 3.97 to 5.73 cm. The results show that ANNs can produce results that are comparable to polynomial fitting and LSC. The main advantage of the ANN-based surfaces seems to be the low deviations from the GPS/levelling data surface, which is particularly important for distorted levelling networks.
In this study, detectability of high-frequency structural vibrations based on only one GNSS recei... more In this study, detectability of high-frequency structural vibrations based on only one GNSS receiver and developed kinematic model solution was investigated. For this purpose, two data sets generated from dual frequency GNSS receiver attached on flexible steel bar(rod) which oscillates one way direction were used. Free decayed sinusoidal oscillation experiments were performed to produce both the first mode and the second mode frequency together. GNSS observations were processed by both the developed kinematic model algorithm and PPP (Precise Point Positioning) method in kinematic mode. Structural vibrations of the rod in time and frequency obtained by both methods were compared. The results have demonstrated that the developed kinematic algorithm can determine high-frequency structural vibrations as much as PPP method. Keywords : Single point kinematic solution, Kinematic-PPP, GPS.
Abstract Since the 1990s, seismic deformations have been commonly determined using the Global Nav... more Abstract Since the 1990s, seismic deformations have been commonly determined using the Global Navigation Satellite System (GNSS). Recently, the GNSS systems have become even more powerful with the use of new technologies in innovative studies. In this study, the GNSS data was used to investigate interseismic, coseismic and postseismic deformation and velocity of the Gokceada-Samothraki earthquake (Mw = 6.9) that occurred on May 24, 2014. The data was obtained at 30 s (0.033 Hz) and 1 s (1 Hz) intervals from the GNSS receivers in the network of Continuously Operating Reference Stations, Turkey (CORS-TR). For the interseismic period, the daily coordinate time series of 12 stations located within 90–250 km of the earthquake epicenter was evaluated for the displacement of stations over a period of approximately 2000 days prior to the day of the earthquakes, from October 1, 2008 to May 23, 2014. In order to analyze the ground motion displacement during the Gokceada-Samothraki earthquake, 1 Hz data from 8 continuous GNSS stations was processed using precise point positioning (PPP) and relative positioning methods to estimate the epoch-by-epoch positions of the stations. During the earthquake, coseismic displacements of approximately 7 and 30 mm were detected in the NW direction at the YENC and CANA stations, respectively. However, at the IPSA station, a coseismic deformation of 20 mm was observed in the NE direction. There were no significant changes at the other stations during the earthquake. For the postseismic period, the daily coordinate time series of the 12 stations were evaluated for station displacements for 570 days after the day of the earthquakes, from May 24, 2014 to January 1, 2016. The results demonstrated that no significant postseismic deformation with the exception of the EDIR station. An abnormal deformation caused by local factors was determined at the EDIR station. In this study, the PPP and the relative solution were also compared in terms of capturing the earthquake wave motion. The results demonstrated that the PPP-based solutions showed good agreement with those of relative positioning in terms of the ability to capture coseismic displacement.
GNSS technology has been extensively used to measure crustal deformation and widely used to const... more GNSS technology has been extensively used to measure crustal deformation and widely used to construct displacement waveforms. GNSS seismology uses GNSS receiver as displacement seismometer for earthquake studies. In other words, it can sense large dynamic displacement without saturation. In GNSS, relative positioning method requires a reference station with no-motion whereas Precise Point Positioning (PPP) method does not need any reference station. However, PPP method, unlike relative positioning method, requires readily precise GNSS satellite orbit and clock product calculated beforehand to perform absolute positioning using a single GNSS receiver data. In case of large earthquake, it may be crucial to select stable reference for relative positioning. Therefore, in order to monitor ground motion pattern caused by the earthquake, PPP method is advantageous because it provides absolute coseismic displacements with respect to a global reference frame. In this study, we investigate th...
Low-cost OEM GPS receivers with the capability of tracking the carrier phase are now used for man... more 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 proj...
The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metre... more 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 kin...
ABSTRACT In recent years, the usage of the Precise Point Positioning (PPP) has increased due to i... more ABSTRACT In recent years, the usage of the Precise Point Positioning (PPP) has increased due to its ease of use, providing high accuracy as well as reducing the field operational costs by using only a single GNSS receiver. Moreover, it does not require any additional reference station data or CORS-like network data. It is a positioning technique that has been extensively investigated and used in a variety of applications, mainly for conventional surveying applications and time-transfer, ionospheric and tropospheric characterization. In GNSS positioning, limited satellite visibility in obstructed areas and poor satellite geometry adversely affect the accuracy of results. With the revitalization of the GLONASS system reaching to full global coverage, PPP studies have focused on combined GPS and GLONASS solutions. The goal of this study is to investigate the usability of PPP technique in urban areas with GPS-only and GPS + GLONASS data by the use of online-PPP services for sub-decimeter surveying applications. For this purpose, test measurements were conducted in Çorum province of Turkey. Collected data were evaluated with two commonly used PPP services, namely CSRS-PPP operated by the Geodetic Survey Division of Natural Resources Canada (NRCan) and magicGNSS/PPP developed by Spanish GMV Aerospace and Defense Co. Results obtained from this study revealed that for some cases, the use of GLONASS with GPS raises the number of satellites used in the solution twice as much as compared to GPS-only. However, unless satellites geometry gets better, the use of GLONASS has no significant role in strengthening the accuracy of results. The results indicate that an increase in the number of satellites is vital especially in urban areas where minimum number of satellites for a solution may not be obtained. Also, it was observed that when the sufficient numbers of GPS satellites with good geometry are available combining GPS together with GLONASS may not bring any significant contribution to the solution.
The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metre... more 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.
The use of GPS for establishing height control in an area where levelling data are available can ... more The use of GPS for establishing height control in an area where levelling data are available can involve the so-called GPS/levelling technique. Modelling of the GPS/levelling geoid undulations has usually been carried out using polynomial surface fitting, least-squares collocation (LSC) and finite-element methods. Artificial neural networks (ANNs) have recently been used for many investigations, and proven to be effective in solving complex problems represented by noisy and missing data. In this study, a feed-forward ANN structure, learning the characteristics of the training data through the back-propagation algorithm, is employed to model the local GPS/levelling geoid surface. The GPS/levelling geoid undulations for Istanbul, Turkey, were estimated from GPS and precise levelling measurements obtained during a field study in the period 1998–99. The results are compared to those produced by two well-known conventional methods, namely polynomial fitting and LSC, in terms of root mean square error (RMSE) that ranged from 3.97 to 5.73 cm. The results show that ANNs can produce results that are comparable to polynomial fitting and LSC. The main advantage of the ANN-based surfaces seems to be the low deviations from the GPS/levelling data surface, which is particularly important for distorted levelling networks.
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missing data. In this study, a feed-forward ANN structure, learning the characteristics of the training data through the back-propagation algorithm, is employed to model the local GPS/levelling geoid surface. The GPS/levelling geoid undulations for Istanbul, Turkey, were estimated from GPS and precise levelling measurements obtained during a field study in
the period 1998–99. The results are compared to those produced by two well-known conventional methods,
namely polynomial fitting and LSC, in terms of root mean square error (RMSE) that ranged from 3.97 to 5.73 cm. The results show that ANNs can produce results that are comparable to polynomial fitting and LSC. The main advantage of the ANN-based surfaces seems to be the low deviations from the GPS/levelling data surface, which is particularly important for distorted levelling networks.
missing data. In this study, a feed-forward ANN structure, learning the characteristics of the training data through the back-propagation algorithm, is employed to model the local GPS/levelling geoid surface. The GPS/levelling geoid undulations for Istanbul, Turkey, were estimated from GPS and precise levelling measurements obtained during a field study in
the period 1998–99. The results are compared to those produced by two well-known conventional methods,
namely polynomial fitting and LSC, in terms of root mean square error (RMSE) that ranged from 3.97 to 5.73 cm. The results show that ANNs can produce results that are comparable to polynomial fitting and LSC. The main advantage of the ANN-based surfaces seems to be the low deviations from the GPS/levelling data surface, which is particularly important for distorted levelling networks.