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  • 1.
    Alizadeh Khameneh, Mohammad Amin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning. WSP Civils, Department of Geographic Information and Asset Management.
    Eshagh, Mehdi
    University West, Department of Engineering Science.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Optimization of Deformation Monitoring Networks using Finite Element Strain Analysis2018In: Journal of Applied Geodesy, ISSN 1862-9016, E-ISSN 1862-9024, Vol. 12, no 2Article in journal (Refereed)
    Abstract [en]

    An optimal design of a geodetic network can fulfill the requested precision and reliability of the network, and decrease the expenses of its execution by removing unnecessary observations. The role of an optimal design is highlighted in deformation monitoring network due to the repeatability of these networks. The core design problem is how to define precision and reliability criteria. This paper proposes a solution, where the precision criterion is defined based on the precision of deformation parameters, i.e. precision of strain and differential rotations. A strain analysis can be performed to obtain some information about the possible deformation of a deformable object. In this study, we split an area into a number of three-dimensional finite elements with the help of the Delaunay triangulation and performed the strain analysis on each element. According to the obtained precision of deformation parameters in each element, the precision criterion of displacement detection at each network point is then determined. The developed criterion is implemented to optimize the observations from the Global Positioning System (GPS) in Skåne monitoring network in Sweden. The network was established in 1989 and straddled the Tornquist zone, which is one of the most active faults in southern Sweden. The numerical results show that 17 out of all 21 possible GPS baseline observations are sufficient to detect minimum 3 mm displacement at each network point.

  • 2.
    Alizadeh Khameneh, Mohammad Amin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. WSP Civils, Department of Geographic Information and Asset Management.
    Horemuž, Milan
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Vium Andersson, Johan
    WSP Civils, Department of Geographic Information and Asset Management.
    Optimal Vertical Placement of Total Station2018In: Journal of Surveying Engineering, ISSN 0733-9453, E-ISSN 1943-5428Article in journal (Refereed)
    Abstract [en]

    When using the free station method, a Total Station (TS) is established by performing distance and angle observations toward a number of Control Points (CPs). The quality of the establishment is crucial for the quality of subsequent measurements. The optimal horizontal location of the TS has been investigated in previous studies. Even the vertical precision is important in many applications, especially with significant height variations. Therefore in this paper, we focus on the optimality of vertical location of the TS. As an optimality criterion, the sum of TS coordinates and orientation variances is used. To investigate the optimization problem, an analytical as well as a trial and error method is developed. Both methods showed that the height component has no significant influence on the optimal vertical placement of the TS. Inspection of results from the trial and error method, where the CPs are moved in different height layers, indicates differences in the height uncertainty of the establishment in micrometer range, which is negligible for most engineering applications.

  • 3.
    Alizadeh Khameneh, Mohammad Amin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. WSP Civils, Department of Geographic Information and Asset Management.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Horemuž, Milan
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Andersson, Johan Vium
    WSP Civils, Department of Geographic Information and Asset Management.
    Investigation of the RUFRIS Method with GNSS and Total Station for Leveling2017Conference paper (Refereed)
    Abstract [en]

    The establishment of leveling benchmarks for performing geodetic measurements, for instance in construction works, is usually costly and laborious due to a mass of field works in transferring the height from nearby known benchmarks. In this study, a real-time updated free station (RUFRIS) method is investigated to be used as an alternative approach for the traditional leveling. The coordinates of a RUFRIS station are determined by establishing a total station on the point, and performing a free-station by observing some points with both Real-Time Kinematic (RTK) GNSS and total station distance and direction observations. The study is conducted based on data from the East Link project in Sweden, where a 150 km long high-speed railway is to be constructed. The results show a standard deviation of 7 mm between the RUFRIS and leveling heights in this project and imply the feasibility of replacing the traditional leveling methods with RUFRIS in projects with low accessibility to benchmarks.

  • 4.
    Alizadeh Khameneh, Mohammad Amin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. WSP Civils, Department of Geographic Information and Asset Management.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Optimisation of GNSS Networks - Considering Baseline Correlations2017In: Survey review - Directorate of Overseas Surveys, ISSN 0039-6265, E-ISSN 1752-2706, p. 1-8Article in journal (Refereed)
    Abstract [en]

    By considering GNSS observations one can perform optimisation according to some pre-defined criteria and come up with the best location of receivers and optimum number of baselines. In practice, it is quite common to neglect the effect of correlations between baselines, and instead assume single-baseline adjusted data in the optimisation procedure. However, in each session of observation usually more than two receivers are simultaneously taking data from a number of common GNSS satellites, implying that the single or double difference observations are correlated. Our study designs an optimal observation plan for a GPS network in Skåne in southern Sweden, with the aim of determining possible displacements. Assuming three receivers in each session of observations leads to correlation between the GPS baselines, and consequently a fully populated weight matrix for each session of observation. A bi-objective optimisation model of precision and reliability is chosen to optimise the variance factor of each session, and eventually, design an observation plan. It is shown in this study that observing 6 out of 10 possible sessions are sufficient to enable the network to detect a 5 mm displacement at each station. Assuming that the double difference phase observations are uncorrelated changes the observation plan by retaining 2 more sessions. However, defining the weight matrix based on the double difference observations requires the correlations to be taken into account, and neglecting them leads to incorrect results.

  • 5.
    Alizadeh Khameneh, Mohammad Amin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. WSP Civils, Department of Geographic Information and Asset Management.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Optimization of GNSS Deformation Monitoring Networks by Considering Baseline Correlations2016In: FIG Working Week 2016 Proceedings, 2016Conference paper (Other academic)
    Abstract [en]

    In the study of deformations of man-made constructions or in geodynamics one usually needs to carefully monitor fixed objects attached to the deformable body. The purpose is to use precise observations to build up an accurate, reliable and possibly low-cost network around the objects to study their motion in short- or long-time intervals and to estimate the possible displacements or deformations among those objects. Frequently, such studies are performed to prevent unwanted disasters (e.g. due to earthquakes and landslides as well as the progressive or abrupt destruction of large-scale structures). This study is concerned with designing an optimal GNSS network to monitor possible deformations of a geodetic network.

    By considering GNSS observations one can perform the optimization according to some pre-defined criteria and come up with the best location of receivers and optimum number of baselines. In practice, it is quite common to neglect the effect of correlations between baselines, and instead use single-baseline adjusted data in the optimisation procedure. However, in each session of observation usually more than two receivers are simultaneously taking data from a number of common GNSS satellites. This procedure inevitably leads to between-baseline correlations. Our study designs an optimal observation plan for a GNSS monitoring network with the aim of determining possible displacements and deformations. The developed methodology will be tested on a simulated network with five points, where three receivers simultaneously take data from four satellites.

  • 6.
    Horemuz, Milan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Analysis of temporal correlation in free station establishment with RTK GNSS2016In: European Journal of Navigation, ISSN 1571-473XArticle in journal (Refereed)
  • 7. Huck, Bastian
    et al.
    Jensen, Anna B. O.
    AJ Geomatics, Denmark.
    Almholt, Anders
    Rüffer, Jürgen
    The Fehmarnbelt Positioning System for a Mega Construction Site2013In: Proceedings of European Navigation Conference 2013 (ENC 2013)., Vienna, Austria: Austrian Institute of Navigation , 2013Conference paper (Other academic)
  • 8.
    Håkansson, Martin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning. Lantmäteriet.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Horemuz, Milan
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Gunnar, Hedling
    Lantmäteriet.
    Review of code and phase biases in multi-GNSS positioning2017In: GPS Solutions, ISSN 1080-5370, E-ISSN 1521-1886, Vol. 21, no 3, p. 849-860Article in journal (Refereed)
    Abstract [en]

    A review of the research conducted until present on the subject of Global Navigation Satellite System (GNSS) hardware-induced phase and code biases is here provided. Biases in GNSS positioning occur because of imperfections and/or physical limitations in the GNSS hardware. The biases are a result of small delays between events that ideally should be simultaneous in the transmission of the signal from a satellite or in the reception of the signal in a GNSS receiver. Consequently, these biases will also be present in the GNSS code and phase measurements and may there affect the accuracy of positions and other quantities derived from the observations. For instance, biases affect the ability to resolve the integer ambiguities in Precise Point Positioning (PPP), and in relative carrier phase positioning when measurements from multiple GNSSs are used. In addition, code biases affect ionospheric modeling when the Total Electron Content is estimated from GNSS measurements. The paper illustrates how satellite phase biases inhibit the resolution of the phase ambiguity to an integer in PPP, while receiver phase biases affect multi-GNSS positioning. It is also discussed how biases in the receiver channels affect relative GLONASS positioning with baselines of mixed receiver types. In addition, the importance of code biases between signals modulated onto different carriers as is required for modeling the ionosphere from GNSS measurements is discussed. The origin of biases is discussed along with their effect on GNSS positioning, and descriptions of how biases can be estimated or in other ways handled in the positioning process are provided.

  • 9. Jakobsen, Jakob
    et al.
    Jensen, Anna B. O.
    AJ Geomatics, Denmark .
    Simulating Non-LOS Reflected GNSS Signals in Urban and Dense Urban Environments2013In: Proceedings of the 26th International Technical Meeting of the Satellite Division of the Institute of Navigation – ION GNSS+ 2013, Manassas, USA: Institute of Navigation, 2013Conference paper (Other academic)
  • 10. Jakobsen, Jakob
    et al.
    Jensen, Anna B. O.
    AJ Geomatics, Denmark.
    Juliet, Marais
    Simulating GNSS Position Accuracy using Non-line of Sight Reflected Signals2013In: Proceedings of European Navigation Conference 2013 (ENC 2013), 2013Conference paper (Other academic)
  • 11. Jakobsen, Jakob
    et al.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Nielsen, Allan Aasbjerg
    Simulation of GNSS reflected signals and estimation of position accuracy in GNSS-challenged environment2015In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 5, no 1, p. 47-56Article in journal (Refereed)
    Abstract [en]

    The paper describes the development and testing of a simulation tool, called QualiSIM. The tool estimates GNSS-based position accuracy based on a simulation of the environment surrounding the GNSS antenna, with a special focus on city-scape environments with large amounts of signal reflections from non-line-of-sight satellites. The signal reflections are implemented using the extended geometric path length of the signal path caused by reflections from the surrounding buildings. Based on real GPS satellite positions, simulated Galileo satellite positions, models of atmospheric effect on the satellite signals, designs of representative environments e.g. urban and rural scenarios, and a method to simulate reflection of satellite signals within the environment we are able to estimate the position accuracy given several prerequisites as described in the paper. The result is a modelling of the signal path from satellite to receiver, the satellite availability, the extended pseudoranges caused by signal reflection, and an estimate of the position accuracy based on a least squares adjustment of the extended pseudoranges. The paper describes the models and algorithms used and a verification test where the results of QualiSIM are compared with results from collection of real GPS data in an environment with much signal reflection.

  • 12.
    Jensen, Anna B. O.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Almholt, Anders
    Geodesy and Positioning for the Fehmarnbelt Fixed Link2014In: Civil Engineering Surveyor, ISSN 0266-139X, Vol. May, p. 19-22Article, review/survey (Other (popular science, discussion, etc.))
  • 13.
    Jensen, Anna B. O.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Almholt, Anders
    Geodetic Infrastructure and Positioning for the Fehmarnbelt Fixed Link2015In: Proceedings of FIG Working Week 2015, 2015Conference paper (Refereed)
  • 14. Ouassou, M.
    et al.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Network real-time kinematic data screening by means of multivariate statistical analysis2019In: SN Applied Science, ISSN 2523-3963, Vol. 1, no 512Article in journal (Refereed)
    Abstract [en]

    We introduce a novel approach to the computation of network real-time kinematic (NRTK) data integrity, which can be used to improve the position accuracy for a rover receiver in the field. Our approach is based on multivariate statistical analysis and stochastic generalized linear model (SGLM). The new approach has an important objective of alarming GNSS network RTK carrier-phase users in case of an error by introducing a multi-layered approach. The network average error corrections and the corresponding variance fields are computed from the data, while the squared Mahalanobis distance (SMD) and Mahalanobis depth (MD) are used as test statistics to detect and remove data from satellites that supply inaccurate data. The variance-covariance matrices are also inspected and monitored to avoid the Heywood effect, i.e. negative variance generated by the processing filters. The quality checks were carried out at both the system and user levels in order to reduce the impact of extreme events on the rover position estimates. The SGLM is used to predict the user carrier-phase and code error statistics. Finally, we present analyses of real-world data sets to establish the practical viability of the proposed methods.

  • 15. Ouassou, M.
    et al.
    Natvig, B.
    Jensen, Anna B. O.
    KTH.
    Gåsemyr, J øI.
    Reliability Analysis of Network Real-Time Kinematic2018In: Journal of Electrical and Computer Engineering, ISSN 2090-0147, E-ISSN 2090-0155, Vol. 2018, article id 8260479Article in journal (Refereed)
    Abstract [en]

    The multistate reliability theory was applied to the network real-time kinematic (NRTK) data processing chain, where the qualities of the network corrections, baseline residuals, and the associated variance-covariance matrices are considered as the system state vectors. The state vectors have direct influence on the rover receiver position accuracy. The penalized honored stochastic averaged standard deviation (PHSASD) is used to map the NRTK sensitive data, represented by the states vectors to different levels of performance. The study shows that the improvement is possible by identification of critical components in the NRTK system and implementation of some parallelism that makes the system more robust.

  • 16. Ouassou, Mohammed
    et al.
    Jensen, Anna B. O.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Gjevestad, Jon Glenn Omholt
    Kristiansen, Oddgeir
    Next Generation Network Real-Time Kinematic Interpolation Segment to Improve the User Accuracy2015In: International Journal of Navigation and Observation, ISSN 1687-5990, E-ISSN 1687-6008, article id 346498Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates that automatic selection of the right interpolation/smoothing method in a GNSS-based network realtime kinematic (NRTK) interpolation segment can improve the accuracy of the rover position estimates and also the processing time in the NRTK processing center. The methods discussed and investigated are inverse distance weighting (IDW); bilinear and bicubic spline interpolation; kriging interpolation; thin-plate splines; and numerical approximation methods for spatial processes. The methods are implemented and tested using GNSS data from reference stations in the Norwegian network RTK service called CPOS.Data sets with an average baseline between reference stations of 60–70 kmwere selected. 12 prediction locations were used to analyze the performance of the interpolation methods by computing and comparing different measures of the goodness of fit such as the root mean square error (RMSE), mean square error, and mean absolute error, and also the computation time was compared. Results of the tests show that ordinary kriging with theMat´ern covariance function clearly provides the best results. The thin-plate spline provides the second best results of the methods selected and with the test data used.

1 - 16 of 16
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