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Optimal Design in Geodetic GNSS-based Networks
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, Stockholm, Sweden.ORCID iD: 0000-0003-1602-4771
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

An optimal design of a geodetic network helps the surveying engineers maximise the efficiency of the network. A number of pre-defined quality requirements, i.e. precision, reliability, and cost, of the network are fulfilled by performing an optimisation procedure. Today, this is almost always accomplished by implementing analytical solutions, where the human intervention in the process cycle is limited to defining the requirements. Nevertheless, a trial and error method can be beneficial to some applications. In order to analytically solve an optimisation problem, it can be classified to different orders, where an optimal datum, configuration, and optimal observation weights can be sought such that the precision, reliability and cost criteria are satisfied.

In this thesis, which is a compilation of six peer-reviewed papers, we optimised and redesigned a number of GNSS-based monitoring networks in Sweden by developing new methodologies. In addition, optimal design and efficiency of total station establishment with RTK-GNSS is investigated in this research.

Sensitivity of a network in detecting displacements is of importance for monitoring purposes. In the first paper, a precision criterion was defined to enable a GNSS-based monitoring network to detect 5 mm displacements at each network point. Developing an optimisation model by considering this precision criterion, reliability and cost yielded a decrease of 17% in the number of observed single baselines implying a reliable and precise network at lower cost. The second paper concerned a case, where the precision of observations could be improved in forthcoming measurements. Thus a new precision criterion was developed to consider this assumption. A significant change was seen in the optimised design of the network for subsequent measurements. As yet, the weight of single baselines was subject to optimisation, while in the third paper, the effect of mathematical correlations between GNSS baselines was considered in the optimisation. Hence, the sessions of observations, including more than two receivers, were optimised. Four out of ten sessions with three simultaneous operating receivers were eliminated in a monitoring network with designed displacement detection of 5 mm. The sixth paper was the last one dealing with optimisation of GNSS networks. The area of interest was divided into a number of three-dimensional elements and the precision of deformation parameters was used in developing a precision criterion. This criterion enabled the network to detect displacements of 3 mm at each point.

A total station can be set up in the field by different methods, e.g. free station or setup over a known point. A real-time updated free station method uses RTK-GNSS to determine the coordinates and orientation of a total station. The efficiency of this method in height determination was investigated in the fourth paper. The research produced promising results suggesting using the method as an alternative to traditional levelling under some conditions. Moreover, an optimal location for the total station in free station establishment was studied in the fifth paper. It was numerically shown that the height component has no significant effect on the optimal localisation.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , p. 72
Series
TRITA-SOM, ISSN 1653-6126 ; 2018-01
National Category
Geotechnical Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
URN: urn:nbn:se:kth:diva-221067ISBN: 978-91-7729-631-7 (print)OAI: oai:DiVA.org:kth-221067DiVA, id: diva2:1173123
Public defence
2018-02-09, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 2080115

Available from: 2018-01-15 Created: 2018-01-11 Last updated: 2018-02-26Bibliographically approved
List of papers
1. Optimisation of Lilla Edet Landslide GPS Monitoring Network
Open this publication in new window or tab >>Optimisation of Lilla Edet Landslide GPS Monitoring Network
2015 (English)In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 5, no 1, p. 57-66Article in journal, Editorial material (Refereed) Published
Abstract [en]

Since the year 2000, some periodic investigations have been performed in the Lilla Edet region to monitor and possibly determine the landslide of the area with the GPS measurements. The responsible consultant has conducted this project by setting up some stable stations for GPS receivers in the risky areas of Lilla Edet and measured the independent baselines amongst the stations according to their observation plan. Here, we optimise the existing surveying network and determine the optimal configuration of the observation plan based on different criteria. We aim to optimise the current network to become sensitive to detect 5 mm possible displacements in each net point. The network quality criteria of precision, reliability and cost are used as object functions to perform single-, bi- and multi-objective optimisation models. It has been shown in the results that the single-objective model of reliability, which is constrained to the precision, provides much higher precision than the defined criterion by preserving almost all of the observations. However, in this study, the multi-objective model can fulfil all the mentioned quality criteria of the network by 17% less measurements than the original observation plan, meaning 17% of saving time, cost and effort in the project.

Keywords
Displacement, Observation plan, Optimisation model, Sensitivity
National Category
Other Civil Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-165406 (URN)10.1515/jogs-2015-0005 (DOI)
Projects
The Swedish Research Council Formas
Funder
Swedish Research Council Formas, 245-2012-356
Note

QC 20150622

Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2018-01-15Bibliographically approved
2. The Effect of Instrumental Precision on Optimisation of Displacement Monitoring Networks
Open this publication in new window or tab >>The Effect of Instrumental Precision on Optimisation of Displacement Monitoring Networks
2016 (English)In: Acta Geodaetica et Geophysica, ISSN 2213-5820, Vol. 51, no 4, p. 761-772Article in journal, Editorial material (Refereed) Published
Abstract [en]

In order to detect the geo-hazards, different deformation monitoring networks are usually established. It is of importance to design an optimal monitoring network to fulfil the requested precision and reliability of the network. Generally, the same observation plan is considered during different time intervals (epochs of observation). Here, we investigate the case that instrumental improvements in sense of precision are used in two successive epochs. As a case study, we perform the optimisation procedure on a GPS monitoring network around the Lilla Edet village in the southwest of Sweden. The network was designed for studying possible displacements caused by landslides. The numerical results show that the optimisation procedure yields an observation plan with significantly fewer baselines in the latter epoch, which leads to saving time and cost in the project. The precision improvement in the second epoch is tested in several steps for the Lilla Edet network. For instance, assuming two times better observation precision in the second epoch decreases the number of baselines from 215 in the first epoch to 143 in the second one.

Keywords
Optimal design, GPS network, Landslide, Observation plan
National Category
Other Civil Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-168312 (URN)10.1007/s40328-015-0150-4 (DOI)000388106100010 ()2-s2.0-85013953894 (Scopus ID)
Projects
The Swedish Research Council Formas
Funder
Swedish Research Council Formas, 245-2012-356
Note

QC 170620

Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2018-01-15Bibliographically approved
3. Optimisation of GNSS Networks - Considering Baseline Correlations
Open this publication in new window or tab >>Optimisation of GNSS Networks - Considering Baseline Correlations
2017 (English)In: Survey review - Directorate of Overseas Surveys, ISSN 0039-6265, E-ISSN 1752-2706, p. 1-8Article in journal, Editorial material (Refereed) Published
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.

Place, publisher, year, edition, pages
Taylor & Francis, 2017
Keywords
correlation, GNSS baselines, network design, displacement, optimisation
National Category
Geotechnical Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-208543 (URN)10.1080/00396265.2017.1342896 (DOI)2-s2.0-85021286843 (Scopus ID)
Note

QC 20170629

Available from: 2017-06-09 Created: 2017-06-09 Last updated: 2018-01-15Bibliographically approved
4. Investigation of the RUFRIS Method with GNSS and Total Station for Leveling
Open this publication in new window or tab >>Investigation of the RUFRIS Method with GNSS and Total Station for Leveling
2017 (English)Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
GNSS, real-time kinematic, free station, leveling
National Category
Geotechnical Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-209184 (URN)10.1109/ICL-GNSS.2017.8376251 (DOI)978-1-5386-2217-9 (ISBN)978-1-5386-2218-6 (ISBN)
Conference
International Conference on Localization and GNSS, Nottingham, UK.
Note

QC 20180115

Available from: 2017-06-16 Created: 2017-06-16 Last updated: 2018-06-13Bibliographically approved
5. Optimal Vertical Placement of Total Station
Open this publication in new window or tab >>Optimal Vertical Placement of Total Station
2018 (English)In: Journal of Surveying Engineering, ISSN 0733-9453, E-ISSN 1943-5428Article in journal, Editorial material (Refereed) Published
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.

National Category
Geotechnical Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-219569 (URN)10.1061/(ASCE)SU.1943-5428.0000255 (DOI)000436097700001 ()2-s2.0-85045743986 (Scopus ID)
Note

QC 20180115

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2018-07-17Bibliographically approved
6. Optimization of Deformation Monitoring Networks using Finite Element Strain Analysis
Open this publication in new window or tab >>Optimization of Deformation Monitoring Networks using Finite Element Strain Analysis
2018 (English)In: Journal of Applied Geodesy, ISSN 1862-9016, E-ISSN 1862-9024, Vol. 12, no 2Article in journal, Editorial material (Refereed) Published
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.

National Category
Geotechnical Engineering
Research subject
Geodesy and Geoinformatics
Identifiers
urn:nbn:se:kth:diva-219571 (URN)10.1515/jag-2017-0040 (DOI)2-s2.0-85045196739 (Scopus ID)
Note

QC 20180115

Available from: 2017-12-07 Created: 2017-12-07 Last updated: 2018-04-04Bibliographically approved

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