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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.
    Eshagh, Mehdi
    et al.
    Univ West, Dept Engn Sci, Trollhattan, Sweden..
    Johansson, Filippa
    Univ West, Dept Engn Sci, Trollhattan, Sweden..
    Karlsson, Lenita
    Univ West, Dept Engn Sci, Trollhattan, Sweden..
    Horemuz, Milan
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    A case study on displacement analysis of Vasa warship2018In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 8, no 1, p. 43-54Article in journal (Refereed)
    Abstract [en]

    Monitoring deformation of man-made structures is very important to prevent them from a risk of collapse and save lives. Such a process is also used for monitoring change in historical objects, which are deforming continuously with time. An example of this is the Vasa warship, which was under water for about 300 years. The ship was raised from the bottom of the sea and is kept in the Vasa museum in Stockholm. A geodetic network with points on the museum building and the ship's body has been established and measured for 12 years for monitoring the ship's deformation. The coordinate time series of each point on the ship and their uncertainties have been estimated epoch-wisely. In this paper, our goal is to statistically analyse the ship's hull movements. By fitting a quadratic polynomial to the coordinate time series of each point of the hull, its acceleration and velocity are estimated. In addition, their significance is tested by comparing them with their respective estimated errors after the fitting. Our numerical investigations show that the backside of the ship, having highest elevation and slope, has moved vertically faster than the other places by a velocity and an acceleration of about 2 mm/year and 0.1 mm/year(2), respectively and this part of the ship is the weakest with a higher risk of collapse. The central parts of the ship are more stable as the ship hull is almost vertical and closer to the floor. Generally, the hull is moving towards its port and downwards.

  • 3.
    Jansson, Patric
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning. Trafikverket.
    Lundgren, Liselotte
    Lidingö kommun.
    A Comparison of Different Methods Using GNSS RTK to Establish Control Points in Cadastral Surveying2018Report (Refereed)
    Abstract [en]

    The purpose of this report is to compare different methods using Global Navigation Satellite System Real Time Kinematic (GNSS RTK) to establish control points to be used for the establishing of a free total station (in the next step). The objectives are to evaluate quality measures for different methods for multiple occupations and the averaging method “180-seconds”. The quality measures used in the study is expanded uncertainty (U95; with 95% level of confidence) and maximum deviation from the true value (“risk”), i.e. the maximum horizontal distance from the mean.From the results in this study, it is clear that it is not only the number of occupations that matters, also the length of the observation periods is important in order to minimize the risk. Extending from one occupation to two (or more) in order to be ‘safe’ is to give a false sense of security.Janssen et al. (2012) stated that an observation window of 1-2 minutes reduces the effects of extreme outliers as much as possible in the shortest time frame. They also concluded that averaging for a longer period than 1-2 minutes does not appear to provide any significant further improvement. In our study, however, increasing the observation window from 1-2 to 3 minutes, are motivated by a decrease in risk (cf. Appendix 1). Further, 180 seconds seem like an eternity for RTK users in the field; consequently, they will use supporting legs for their antenna pole. Using a shorter averaging time (60-120 s), this is not always obvious for the user. Consequently, extending the observation window to 3 minutes is motivated by a decrease in risk and a decrease in centering error. Therefore, the recommendation is to use observation periods of at least 180 seconds (3 min) of data. This is according to the recommendations given in Edwards et al. (2010).There is a trade-off between the recommendation of using as many observations as possible, i.e. at least two occupations with at least 3 minutes length of every observation periods, and productivity. This task must be carefully balanced by the surveyor in a case-by-case evaluation.Regarding productivity, averaging over 180 seconds of data at only one occupation seems to be a proper balance for cadastral surveying. According to this study it is not significantly worse than the mean of the eleven different multiple occupations methods in this study.

  • 4.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Topographic effects in geoid determinations2018In: Geosciences (Switzerland), ISSN 2076-3263, Vol. 8, no 4, article id 143Article in journal (Refereed)
    Abstract [en]

    Traditionally, geoid determination is applied by Stokes’ formula with gravity anomalies after removal of the attraction of the topography by a simple or refined Bouguer correction, and restoration of topography by the primary indirect topographic effect (PITE) after integration. This technique leads to an error of the order of the quasigeoid-to-geoid separation, which is mainly due to an incomplete downward continuation of gravity from the surface to the geoid. Alternatively, one may start from the modern surface gravity anomaly and apply the direct topographic effect on the anomaly, yielding the no-topography gravity anomaly. After downward continuation of this anomaly to sea-level and Stokes integration, a theoretically correct geoid height is obtained after the restoration of the topography by the PITE. The difference between the Bouguer and no-topography gravity anomalies (on the geoid or in space) is the “secondary indirect topographic effect”, which is a necessary correction in removing all topographic signals. In modern applications of an Earth gravitational model (EGM) in geoid determination a topographic correction is also needed in continental regions. Without the correction the error can range to a few metres in the highest mountains. The remove-compute-restore and Royal Institute of Technology (KTH) techniques for geoid determinations usually employ a combination of Stokes’ formula and an EGM. Both techniques require direct and indirect topographic corrections, but in the latter method these corrections are merged as a combined topographic effect on the geoid height. Finally, we consider that any uncertainty in the topographic density distribution leads to the same error in gravimetric and geometric geoid estimates, deteriorating GNSS-levelling as a tool for validating the topographic mass distribution correction in a gravimetric geoid model.

  • 5.
    Tenzer, Robert
    et al.
    Hong Kong Polytech Univ, Dept Land Surveying & Geoinformat, 181 Chatham Rd South, Kowloon, Hong Kong, Peoples R China..
    Chen, Wenjin
    Wuhan Univ, Dept Geodesy & Geomat, Wuhan, Hubei, Peoples R China..
    Baranov, Alexey
    Russian Acad Sci, Schmidt Inst Phys Earth, Moscow, Russia.;Russian Acad Sci, Inst Earthquake Predict Theory & Math Geophys, Moscow, Russia..
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Gravity Maps of Antarctic Lithospheric Structure from Remote-Sensing and Seismic Data2018In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 175, no 6, p. 2181-2203Article in journal (Refereed)
    Abstract [en]

    Remote-sensing data from altimetry and gravity satellite missions combined with seismic information have been used to investigate the Earth's interior, particularly focusing on the lithospheric structure. In this study, we use the subglacial bedrock relief BEDMAP2, the global gravitational model GOCO05S, and the ETOPO1 topographic/bathymetric data, together with a newly developed (continental-scale) seismic crustal model for Antarctica to compile the free-air, Bouguer, and mantle gravity maps over this continent and surrounding oceanic areas. We then use these gravity maps to interpret the Antarctic crustal and uppermost mantle structure. We demonstrate that most of the gravity features seen in gravity maps could be explained by known lithospheric structures. The Bouguer gravity map reveals a contrast between the oceanic and continental crust which marks the extension of the Antarctic continental margins. The isostatic signature in this gravity map confirms deep and compact orogenic roots under the Gamburtsev Subglacial Mountains and more complex orogenic structures under Dronning Maud Land in East Antarctica. Whereas the Bouguer gravity map exhibits features which are closely spatially correlated with the crustal thickness, the mantle gravity map reveals mainly the gravitational signature of the uppermost mantle, which is superposed over a weaker (long-wavelength) signature of density heterogeneities distributed deeper in the mantle. In contrast to a relatively complex and segmented uppermost mantle structure of West Antarctica, the mantle gravity map confirmed a more uniform structure of the East Antarctic Craton. The most pronounced features in this gravity map are divergent tectonic margins along mid-oceanic ridges and continental rifts. Gravity lows at these locations indicate that a broad region of the West Antarctic Rift System continuously extends between the Atlantic-Indian and Pacific-Antarctic mid-oceanic ridges and it is possibly formed by two major fault segments. Gravity lows over the Transantarctic Mountains confirms their non-collisional origin. Additionally, more localized gravity lows closely coincide with known locations of hotspots and volcanic regions (Marie Byrd Land, Balleny Islands, Mt. Erebus). Gravity lows also suggest a possible hotspot under the South Orkney Islands. However, this finding has to be further verified.

  • 6.
    Uggla, Gustaf
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Horemuz, Milan
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management, Geodesy and Satellite Positioning.
    Georeferencing Methods for IFC2018In: Proceedings - 2018 Baltic Geodetic Congress, BGC-Geomatics 2018, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 207-211Conference paper (Refereed)
    Abstract [en]

    Building Information Modelling (BIM) is becoming a standard tool for information management throughout the life cycle of a construction project. Elements in BIM are designed in a Cartesian coordinate system (Engineering system) with no direct relation to the project's geographic location. Accurate georeferencing of BIM data is required both for construction and integration with Geographic Information Systems (GIS), as improperly treated or neglected scale distortions can lead to costly delays in construction as problems requiring ad hoc solutions may arise on site Industry Foundation Classes (IFC) is an open BIM standard developed by buildingSMART, and the current version IFC 4 has recently been extended with IFC Alignment, which includes support for alignment geometries used for infrastructure design. This paper investigates the geographic capabilities of IFC 4 and its extension IFC Alignment. The study identifies a lack of support for non-uniform scale factors and object-specific map projections as the largest weaknesses.

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