scholarly journals A Tale of Five Bridges; the use of GNSS for Monitoring the Deflections of Bridges

2014 ◽  
Vol 8 (4) ◽  
Author(s):  
Gethin Wyn Roberts ◽  
Christopher J. Brown ◽  
Xu Tang ◽  
Xiaolin Meng ◽  
Oluropo Ogundipe
Keyword(s):  
Carrier Phase ◽  
Suspension Bridge ◽  
Single Frequency ◽  
Gps Data ◽  
Dual Frequency ◽  
Bridge Monitoring ◽  
Gnss Receivers ◽  
Rtk Gps ◽  
Millennium Bridge ◽  
Gathering Data

AbstractThe first Bridge Monitoring surveying was carried out in 1996 by the authors, through attaching Ashtech ZXII GPS receivers onto the Humber Bridge’ parapet, and gathering and further analysing the resulting 1 Hz RTK GPS data. Various surveys have subsequently been conducted on the Humber Bridge, the Millennium Bridge, the Forth Road Bridge, the Severn Suspension Bridge and the Avonmouth Viaduct. These were all carried out using survey grade carrier phase/pseudorange GPS and later GNSS receivers. These receivers were primarily dual frequency receivers, but the work has also investigated the use of single frequency receivers, gathering data at 1 Hz, 10 Hz, 20 Hz and even 100 Hz. Various aspects of the research conducted are reported here, as well as the historical approach. Conclusions are shown in the paper, as well as lessons learnt during the development of this work. The results are compared to various models that exist of the bridges’ movements, and compare well. The results also illustrate that calculating the frequencies of the movements, as well as looking at the magnitudes of the movements, is an important aspect of this work. It is also shown that in instances where the magnitudes of the movements of the bridge under investigation are small, it is still possible to derive very accurate frequencies of the movements, in comparison to the existing models.

scholarly journals DEVELOPMENT AND EVALUATION OF A UAV BASED MAPPING SYSTEM FOR REMOTE SENSING AND SURVEYING APPLICATIONS

2015 ◽  
Vol XL-1/W4 ◽  
pp. 233-239 ◽  
Author(s):  
C. Eling ◽  
M. Wieland ◽  
C. Hess ◽  
L. Klingbeil ◽  
H. Kuhlmann
Keyword(s):  
Remote Sensing ◽  
Reference Point ◽  
Time Synchronization ◽  
Low Cost ◽  
Single Point ◽  
Single Frequency ◽  
Dual Frequency ◽  
Lever Arm ◽  
Rtk Gps ◽  
Camera Synchronization

In recent years, unmanned aerial vehicles (UAVs) have increasingly been used in various application areas, such as in the remote sensing or surveying. For these applications the UAV has to be equipped with a mapping sensor, which is mostly a camera. Furthermore, a georeferencing of the UAV platform and/or the acquired mapping data is required. The most efficient way to realize this georeferencing is the direct georeferencing, which is based on an onboard multi-sensor system. In recent decades, direct georeferencing systems have been researched and used extensively in airborne, ship and land vehicle applications. However, these systems cannot easily be adapted to UAV platforms, which is mainly due to weight and size limitations. <br><br> In this paper a direct georeferencing system for micro- and mini-sized UAVs is presented, which consists of a dual-frequency geodetic grade OEM GPS board, a low-cost single-frequency GPS chip, a tactical grade IMU and a magnetometer. To allow for cm-level position and sub-degree attitude accuracies, RTK GPS (real-time kinematic) and GPS attitude (GPS compass) determination algorithms are running on this system, as well as a GPS/IMU integration. <br><br> Beside the direct georeferencing, also the precise time synchronization of the camera, which acts as the main sensor for mobile mapping applications, and the calibration of the lever arm between the camera reference point and the direct georeferencing reference point are explained in this paper. Especially the high accurate time synchronization of the camera is very important, to still allow for high surveying accuracies, when the images are taken during the motion of the UAV. <br><br> Results of flight tests demonstrate that the developed system, the camera synchronization and the lever arm calibration make directly georeferenced UAV based single point measurements possible, which have cm-level accuracies on the ground.

scholarly journals Comparison of Multi-GNSS Time and Frequency Transfer Performance Using Overlap-Frequency Observations

2021 ◽  
Vol 13 (16) ◽  
pp. 3130
Author(s):  
Pengfei Zhang ◽  
Rui Tu ◽  
Yuping Gao ◽  
Ju Hong ◽  
Junqiang Han ◽  
...  
Keyword(s):  
Carrier Phase ◽  
Satellite System ◽  
Single Frequency ◽  
Navigation Satellite ◽  
Transfer Performance ◽  
Dual Frequency ◽  
Time Transfer ◽  
Difference Series ◽  
Frequency Transfer ◽  
Global Navigation Satellite

The modernized GPS, Galileo, and BeiDou global navigation satellite system (BDS3) offers new potential for time transfer using overlap-frequency (L1/E1/B1, L5/E5a/B2a) observations. To assess the performance of time and frequency transfer with overlap-frequency observations for GPS, Galileo, and BDS3, the mathematical models of single- and dual-frequency using the carrier-phase (CP) technique are discussed and presented. For the single-frequency CP model, the three-day average RMS values of the L5/E5a/B2a clock difference series were 0.218 ns for Galileo and 0.263 ns for BDS3, of which the improvements were 36.2% for Galileo and 43.9% for BDS3 when compared with the L1/E1/B1 solution at BRUX–PTBB. For the hydrogen–cesium time link BRUX–KIRU, the RMS values of the L5/E5a/B2a solution were 0.490 ns for Galileo and 0.608 ns for BDS3, improving Galileo by 6.4% and BDS3 by 12.5% when compared with the L1/E1/B1 solution. For the dual-frequency CP model, the average stability values of the L5/E5a/B2a solution at the BRUX–PTBB time link were 3.54∙× 10−12 for GPS, 2.20 × 10−12 for Galileo, and 2.69 × 10−12 for BDS3, of which the improvements were 21.0%, 45.1%, and 52.3%, respectively, when compared with the L1/E1/B1 solution. For the BRUX–KIRU time link, the improvements were 4.2%, 30.5%, and 36.1%, respectively.

scholarly journals Impact of UAS Image Orientation on Accuracy of Forest Inventory Attributes

2020 ◽  
Vol 12 (3) ◽  
pp. 404 ◽  
Author(s):  
Luka Jurjević ◽  
Mateo Gašparović ◽  
Anita Simic Milas ◽  
Ivan Balenović
Keyword(s):  
Carrier Phase ◽  
Single Frequency ◽  
Pedunculate Oak ◽  
Dual Frequency ◽  
3D Point Clouds ◽  
Sensor Orientation ◽  
Forested Areas ◽  
Gnss Measurements ◽  
Image Orientation ◽  
Gnss Data

The quality and accuracy of Unmanned Aerial System (UAS) products greatly depend on the methods used to define image orientations before they are used to create 3D point clouds. While most studies were conducted in non- or partially-forested areas, a limited number of studies have evaluated the spatial accuracy of UAS products derived by using different image block orientation methods in forested areas. In this study, three image orientation methods were used and compared: (a) the Indirect Sensor Orientation (InSO) method with five irregularly distributed Ground Control Points (GCPs); (b) the Global Navigation Satellite System supported Sensor Orientation (GNSS-SO) method using non-Post-Processed Kinematic (PPK) single-frequency carrier-phase GNSS data (GNSS-SO1); and (c) using PPK dual-frequency carrier-phase GNSS data (GNSS-SO2). The effect of the three methods on the accuracy of plot-level estimates of Lorey’s mean height (HL) was tested over the mixed, even-aged pedunculate oak forests of Pokupsko basin located in Central Croatia, and validated using field validation across independent sample plots (HV), and leave-one-out cross-validation (LOOCV). The GNSS-SO2 method produced the HL estimates of the highest accuracy (RMSE%: HV = 5.18%, LOOCV = 4.06%), followed by the GNSS-SO1 method (RMSE%: HV = 5.34%, LOOCV = 4.37%), while the lowest accuracy was achieved by the InSO method (RMSE%: HV = 5.55%, LOOCV = 4.84%). The negligible differences in the performances of the regression models suggested that the selected image orientation methods had no considerable effect on the estimation of HL. The GCPs, as well as the high image overlaps, contributed considerably to the block stability and accuracy of image orientation in the InSO method. Additional slight improvements were achieved by replacing single-frequency GNSS measurements with dual-frequency GNSS measurements and by incorporating PPK into the GNSS-SO2 method.

scholarly journals Potential of Cost-Efficient Single Frequency GNSS Receivers for Water Vapor Monitoring

2018 ◽  
Vol 10 (9) ◽  
pp. 1493 ◽  
Author(s):  
Andreas Krietemeyer ◽  
Marie-claire ten Veldhuis ◽  
Hans van der Marel ◽  
Eugenio Realini ◽  
Nick van de Giesen
Keyword(s):  
Water Vapor ◽  
Low Cost ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Small Scale ◽  
Reference Network ◽  
Tropospheric Delay ◽  
Dual Frequency ◽  
Gnss Receivers ◽  
Cost Efficient

Dual-frequency Global Navigation Satellite Systems (GNSSs) enable the estimation of Zenith Tropospheric Delay (ZTD) which can be converted to Precipitable Water Vapor (PWV). The density of existing GNSS monitoring networks is insufficient to capture small-scale water vapor variations that are especially important for extreme weather forecasting. A densification with geodetic-grade dual-frequency receivers is not economically feasible. Cost-efficient single-frequency receivers offer a possible alternative. This paper studies the feasibility of using low-cost receivers to increase the density of GNSS networks for retrieval of PWV. We processed one year of GNSS data from an IGS station and two co-located single-frequency stations. Additionally, in another experiment, the Radio Frequency (RF) signal from a geodetic-grade dual-frequency antenna was split to a geodetic receiver and two low-cost receivers. To process the single-frequency observations in Precise Point Positioning (PPP) mode, we apply the Satellite-specific Epoch-differenced Ionospheric Delay (SEID) model using two different reference network configurations of 50–80 km and 200–300 km mean station distances, respectively. Our research setup can distinguish between the antenna, ionospheric interpolation, and software-related impacts on the quality of PWV retrievals. The study shows that single-frequency GNSS receivers can achieve a quality similar to that of geodetic receivers in terms of RMSE for ZTD estimations. We demonstrate that modeling of the ionosphere and the antenna type are the main sources influencing the ZTD precision.

scholarly journals Georeferencing experiments with UAS imagery

2014 ◽  
Vol II-1 ◽  
pp. 25-29 ◽  
Author(s):  
G. Jóźków ◽  
C. Toth
Keyword(s):  
Low Cost ◽  
Field Work ◽  
Single Frequency ◽  
Gps Data ◽  
Dual Frequency ◽  
Quality Of Data ◽  
Advantages And Disadvantages ◽  
Ground Control Points ◽  
Active Imaging ◽  
Application Potential

Comparing typical airborne mapping systems with Unmanned Airborne Systems (UAS) developed for mapping purposes, there are several advantages and disadvantages of both systems. The unquestionable benefits of UAS are the much lower costs of equipment and the simple operation; though, the regulations to fly UAS greatly vary by country. Low cost, however, means small sensor size and low weight, thus, sensors usually lack the quality, negatively impacting the accuracy of UAS data and, consequently, any derived mapping products. This work compares the performance of three different positioning approaches used for UAS image geolocation. The first one is based on using dual-frequency GPS data, post-processed in kinematic mode. The second approach uses the single frequency, code only GPS data that was acquired and processed by a geotagger, attached to mapping camera. Finally, the third one employs indirect image georeferencing, based on aerial triangulation using ground controls. As expected, the quality of data provided by the inexpensive GPS receiver (geotagger) is not suitable for mapping purposes. The two other approaches provided similar and reliable results, confirming that commonly used indirect georeferencing, which usually assures good solution, can be replaced by direct georeferencing. The latter technique results not only in reduction of field work, e.g. Ground Control Points (GCPs) surveying, but is appropriate for use with other sensors, such as active imaging technology, LiDAR, further extending UAS application potential.

scholarly journals Experimental Analysis of Navigational Precision for Dedicated GNSS Receivers

2016 ◽  
Vol 10 (4) ◽  
pp. 253-257 ◽  
Author(s):  
Maciej Słowik ◽  
Tomasz Mrozek
Keyword(s):  
Quality Parameters ◽  
Base Station ◽  
Single Frequency ◽  
Experimental Investigations ◽  
Dual Frequency ◽  
Simultaneous Acquisition ◽  
Gnss Receivers ◽  
Differential Corrections ◽  
Mobile Receiver ◽  
Minimum Numbers

Abstract In the paper experimental investigations related with analysis of navigational precision of three chosen GNSS receivers are shown. Used receivers allow for measurement of navigational signals in following modes of operations: receiving signals from single-frequency GPS system, dual-frequency GPS/GLONASS system, and receiving signals from GPS constellation with use of differential measurements. In the last mode the base station and mobile receiver were configured for transmitting/receiving differential corrections by pair of industry-grade radio modems. The most important features and configuration of navigational receivers for conducted experiment are presented. Afterward the features of computer program designed especially for simultaneous acquisition, analysis of quality parameters and archiving of navigational signals are shown. The results of conducted investigations are also shown. For each of the receivers quantity and quality parameters such as maximum and minimum numbers of visible satellites and DOP (dilution of precision) parameters achieved during the experiment are given.

Impact of New GPS Signals on Positioning Accuracy for Urban Bus Operations

2020 ◽  
Vol 73 (6) ◽  
pp. 1284-1305
Author(s):  
Mireille Elhajj ◽  
Washington Ochieng
Keyword(s):  
Carrier Phase ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Dimensional Accuracy ◽  
Single Frequency ◽  
Measurement Unit ◽  
Dual Frequency ◽  
Positioning Accuracy ◽  
Phase Measurements ◽  
The Impact

This paper analyses for the first time the impact of new GPS signals on positioning accuracy for dynamic urban applications, taking bus operations as an example. The performance assessment addresses both code measurement precision and positioning accuracy. The former is based on signal-to-noise ratio and estimation of multipath and noise by a combination of code and carrier phase measurements. The impact on positioning accuracy is derived by comparing the performance achievable with the conventional single frequency GPS only positioning both relative to reference trajectories from the integration of carrier phase measurements with data from a high grade inertial measurement unit. The results show that L5 code measurements have the highest precision, followed by L1 C/A and L2C. In the positioning domain, there is a significant improvement in two-dimensional and three-dimensional accuracy from dual frequency code measurements over the single frequency measurements, of 39% and 48% respectively, enabling more bus operation services to be supported.

scholarly journals Snow Depth Estimation with GNSS-R Dual Receiver Observation

2019 ◽  
Vol 11 (17) ◽  
pp. 2056 ◽  
Author(s):  
Yu ◽  
Wang ◽  
Li ◽  
Chang ◽  
Li
Keyword(s):  
Snow Depth ◽  
Carrier Phase ◽  
Mean Squared Error ◽  
Depth Estimation ◽  
Combination Method ◽  
Estimation Methods ◽  
Single Frequency ◽  
Dual Frequency ◽  
Combination Methods ◽  
Receiver System

Two estimation methods using a dual GNSS (Global Navigation Satellite System) receiver system are proposed. The dual-frequency combination method combines the carrier phase observations of dual-frequency signals, whereas the single-frequency combination method combines the pseudorange and carrier phase observations of a single-frequency signal, both of which are geometry-free strictly combination and free of the effect of ionospheric delay. Theoretical models are established in the offline phase to describe the relationship between the spectral peak frequency of the combined sequence and the antenna height. A field experiment was conducted recently and the data processing results show that the root mean squared error (RMSE) of the dual-frequency combination method is 5.04 cm with GPS signals and 6.26 cm with BDS signals, which are slightly greater than the RMSE of 4.16 cm produced by the single-frequency combination method of L1 band with GPS signals. The results also demonstrate that the proposed two combination methods and the SNR method achieve similar performance. A dual receiver system enables the better use of GNSS signal carrier phase observations for snow depth estimation, achieving increased data utilization.

scholarly journals Registration of ionospheric effect of 20 March 2015 solar eclipse from GPS data in single-frequency mode

2015 ◽  
Vol 1 (4) ◽  
pp. 35-39 ◽  
Author(s):  
Олег Горбачев ◽  
Oleg Gorbachev ◽  
Всеволод Иванов ◽  
Vsevolod Ivanov ◽  
Андрей Холмогоров ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Quantitative Agreement ◽  
Single Frequency ◽  
Gps Data ◽  
Electron Content ◽  
Time Behavior ◽  
Dual Frequency ◽  
Total Electron ◽  
Appropriate Treatment ◽  
Time Courses

The paper objective is to demonstrate the possibility of studying irregular variations of the total electron content (TEC) of the ionosphere using GPS data of single-frequency measurements. This is considered by the example of registering the time behavior of the oblique TEC during the 20 March 2015 solar eclipse. As the initial data, we used single-frequency and dual-frequency phase and code measurements from the station MORP which is a part of the International IGS Network. As a result, by comparing the data of TEC time courses for two modes it is shown both qualitative agreement (TEC significant decrease during the eclipse) and quantitative agreement of results after appropriate treatment.

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