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  • 251.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    A rigorous formula for geoid-to-quasigeoid separation2010Conference paper (Refereed)
  • 252.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Closed-form and iterative weighted least squares solutions of Helmert transformation parameters2013In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 3, no 1, p. 7-11Article in journal (Refereed)
    Abstract [en]

    The Helmert transformation is the most common transformation between different geodetic systems. In 2-D, in contrast to higher dimensions, it is a well-known procedure how to determine the 4 transformation parameters in a closed form. Here we derive the closed-form weighted least squares solution in m-dimensional space for an arbitrary number (≥ m) of coordinate set-ups in two related systems. The solution employs singular value decomposition (SVD) for the rotation matrix, while the translation vector and scale parameters are obtained in simpler ways. To avoid the SVD routine, we also present an iterative approach to solve for the rotation matrix. The paper is completed with a test procedure for detecting outlying coordinate pairs. 

  • 253.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Comments to X. Li and Y. M. Wang (2011) Comparisons of geoid models over Alaska computed with different Stokes' kernel modifications, JGS 1(2): 136-1422012In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 2, no 1, p. 136-142Article in journal (Refereed)
    Abstract [en]

    Li and Wang recently compared geoid determination by various gravimetric methods for modifying Stokes' formula vs. using GPS/levelling geoid heights as a reference model. Possible large systematic errors in the differences of gravimetric and GPS/levelling geoid models deteriorate the results and conclusions. Moreover, spectral combination, the only stochastic method in the study, was applied in an unrealistic way.

  • 254.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Erik W. Grafarend and Joseph L. Awange: Applications of Linear and Nonlinear Models – Fixed Effects, Random Effects, and Total Least Squares2013In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 3, no 1, p. 77-78Article, book review (Other academic)
  • 255.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Geoid determination by spectral combination of an Earth gravitational model with airborne and terrestrial gravimetry - a theoretical study2011In: Studia Geophysica et Geodaetica, ISSN 0039-3169, E-ISSN 1573-1626, Vol. 55, no 4, p. 579-588Article in journal (Refereed)
    Abstract [en]

    Today air-gravimetry is a versatile technique to quickly collect gravity data over large regions, where terrestrial gravity data are sparse and/or of poor quality. The method requires the data to be downward continued to sea level for use in geoid determination, an inverse problem operation that calls for smoothing of the data and/or the kernel function involved (in either spectral or space domain). In this purely theoretical study we avoid this separate computational step by performing direct geoid estimation by so-called spectral combination/filtering of the data, which includes terrestrial gravimetry, airgravimetry, an Earth Gravitational Model (EGM) as well as their signal and error degree variances. Each derived geoid estimator is presented as the sum of one or two integral formulas and the harmonic series of the EGM together with the expected mean square error of the estimator. The article is limited to a theoretical study, leaving its practical tests for future investigation.

  • 256.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    New solutions for the geoid potential W0 and the Mean Earth Ellipsoid dimensions2013In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 3, no 4, p. 258-265Article in journal (Refereed)
    Abstract [en]

    Earth Gravitational Models (EGMs) describe the Earth’s gravity field including the geoid, except for its zero-degree harmonic, which is a scaling parameter that needs a known geometric distance for its calibration. Today this scale can be provided by the absolute geoid height as estimated from satellite altimetry at sea. On the contrary, the above technique cannot be used to determine the geometric parameters of the Mean Earth Ellipsoidal (MEE), as this problem needs global data of both satellite altimetry and gravimetric geoid models, and the standard technique used today leads to a bias for the unknown zero-degree harmonic of the gravimetric geoid height model. Here we present a new method that eliminates this problem and simultaneously determines the potential of the geoid (W0) and the MEE axes. As the resulting equations are non-linear, the linearized observation equations are also presented. 

  • 257.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    On the isostatic gravity anomaly and disturbance and their applications to vening meinesz-moritz gravimetric inverse problem2013In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 193, no 3, p. 1277-1282Article in journal (Refereed)
    Abstract [en]

    In this study,we showthat the traditionally defined Bouguer gravity anomaly needs a correction to become 'the no-topography gravity anomaly' and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the Bouguer gravity anomaly plus a gravitational compensation effect. This is because only the newisostatic gravity anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic gravity anomaly. We show how the Moho geometry can be solved for the gravity anomaly, gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same.

  • 258.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    On the topographic effects by Stokes’ formula2014In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 4, no 1, p. 130-135Article in journal (Refereed)
    Abstract [en]

    Traditional gravimetric geoid determination relies on Stokes’ formula with removal and restoration of the topographic effects. It is shown that this solution is in error of the order of the quasigeoid-to-geoid difference, which is mainly due to incomplete downward continuation (dwc) of gravity from the Earth’s surface to the geoid. A slightly improved estimator, based on the surface Bouguer gravity anomaly, is also biased due to the imperfect harmonic dwc the Bouguer anomaly. Only the third estimator,which uses the (harmonic) surface no-topography gravity anomaly, is consistent with the boundary condition and Stokes’ formula, providing a theoretically correct geoid height. 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. 

  • 259.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Quality Estimates in Geoid Computation by EGM082011In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 1, no 4, p. 361-366Article in journal (Refereed)
    Abstract [en]

    The high-degree Earth Gravitational Model EGM08 allows for geoid determination with a resolution of the order of 5'. Using this model for estimating the quasigeoid height, we estimate the global root mean square (rms) commission error to 5 and 11 cm, based on the assumptions that terrestrial gravity contributes to the model with an rms standard error of 5 mGal and correlation length 0:01° and 0:1°, respectively. The omission error is estimated to—0:7Δg [mm], where Δg is the regional mean gravity anomaly in units of mGal.

    In case of geoid determination by EGM08, the topographic bias must also be considered. This is because the Earth's gravitational potential, in contrast to its spherical harmonic representation by EGM08, is not a harmonic function at the geoid inside the topography. If a correction is applied for the bias, the main uncertainty that remains is that from the uncertainty in the topographic density, which will still contribute to the overall geoid error.

  • 260.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Rigorous geoid-from-quasigeoid correction using gravity disturbances2015In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943Article in journal (Refereed)
  • 261.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Solutions to Linear Inverse Problems on the Sphere by Tikhonov Regularization, Wiener filtering and Spectral Smoothing and Combination — A Comparison2012In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 2, no 1, p. 31-37Article in journal (Refereed)
    Abstract [en]

    Solutions to linear inverse problems on the sphere, common in geodesy and geophysics, are compared for Tikhonov's method of regularization, Wiener filtering and spectral smoothing and combination as well as harmonic analysis. It is concluded that Wiener and spectral smoothing, although based on different assumptions and target functions, yield the same estimator. Also, provided that the extra information on the signal and error degree variances is available, the standard Tikhonov method is inferior to the other methods, which, in contrast to Tikhonov's approach, match the spectral errors and signals in an optimum way. We show that the corresponding Tikhonov matrix for optimum regularization can only be determined approximately. Moreover, as Tikhonov's method solves an integral equation, it is less computationally efficient than the other methods, which use forward integration. Also harmonic analysis uses direct integration and is not hampered, as previous methods, with spectral leakage. Spectral combination, in addition to filtering, has the advantage of combining different data sets by least squares spectral weighting.

  • 262.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Solutions to the direct and inverse navigation problems on the great ellipse2012In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 2, no 3, p. 200-205Article in journal (Refereed)
    Abstract [en]

    The Great Ellipse (GE) is the curve of intersection between the surface and a plane through the center of an ellipsoid. For arcs within a few thousands of kilometres it agrees within a few metres with the geodesic. As the direct and indirect navigation problems for the GE can be solved almost entirely by closed formulas (in contrast to the corresponding geodetic problems of the geodesic), navigation on the GE is mostly preferred. Here we take advantage of the Clairaut constant on the GE in solving the navigation problems.

  • 263.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Solutions to the ellipsoidal Clairaut constant and the inverse geodetic problem by numerical integration2012In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 2, no 3, p. 162-171Article in journal (Refereed)
    Abstract [en]

    We derive computational formulas for determining the Clairaut constant, i.e. the cosine of the maximum latitude of the geodesic arc, from two given points on the oblate ellipsoid of revolution. In all cases the Clairaut constant is unique. The inverse geodetic problem on the ellipsoid is to determine the geodesic arc between and the azimuths of the arc at the given points. We present the solution for the fixed Clairaut constant. If the given points are not(nearly) antipodal, each azimuth and location of the geodesic is unique, while for the fixed points in the ”antipodal region”, roughly within 36”.2 from the antipode, there are two geodesics mirrored in the equator and with complementary azimuths at each point. In the special case with the given points located at the poles of the ellipsoid, all meridians are geodesics. The special role played by the Clairaut constant and the numerical integration make this method different from others available in the literature.

  • 264.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    The geoid or quasigeoid – which reference surface should be preferred for a national height system?2013In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 3, no 2, p. 103-109Article in journal (Refereed)
    Abstract [en]

    Most European states use M. S. Molodensky’s concept of normal heights for their height systems with a quasigeoid model as the reference surface, while the rest of the world rely on orthometric heights with the geoid as the zero-level. Considering the advances in data caption and theory for geoid and quasigeoid determinations, the question is which system is the best choice for the future. It is reasonable to assume that the latter concept, in contrast to the former, will always suffer from some uncertainty in the topographic density distribution, while Molodensky’s approach to quasigeoid determination has a convergence problem. On the contrary, geoid and quasigeoid models computed by analytical continuation (e.g., rcr technique or KTH method) have no integration problem, and the quasigeoid can always be determined at least as accurate as the geoid. As the numerical instability of the analytical continuation is better controlled in the KTH method vs. the rcr method, we propose that any future height system be based on normal heights with a quasigeoid model computed similar to or directly based on the KTH method (Least squares modification of Stokes formula with additive corrections).

  • 265.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    The geoid-to-quasigeoid difference using an arbitrary gravity reduction model2012In: Studia Geophysica et Geodaetica, ISSN 0039-3169, E-ISSN 1573-1626, Vol. 56, no 4, p. 929-933Article in journal (Refereed)
    Abstract [en]

    Recently it was proved that the classical formula for computing the geoid to quasigeoid separation (GQS) by the Bouguer gravity anomaly needs a topographic correction. Here we generalize the modelling of the GQS not only to Bouguer types of anomalies, hut also to arbitrary reductions of topographic gravity. Of particular interest for practical applications should be isostatic and Helmert types of reductions, which provide smaller and smoother components, more suitable for interpolation and calculation, than the Bouguer reduction.

  • 266.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    The KTH approach to Modelling the Geoid- Extended lecture notes, KTH2013Report (Refereed)
  • 267.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    A numerical study of the analytical downward continuation error in geoid computation by EGM082011In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 1, no 1, p. 2-8Article in journal (Refereed)
    Abstract [en]

    Today the geoid can be conveniently determined by a set of high-degree spherical harmonics, such as EGM08 with a resolution of about 5'. However, such a series will be biased when applied to the continental geoid inside the topographic masses. This error we call the analytical downward continuation (DWC) error, which is closely related with the so-called topographic potential bias. However, while the former error is the result of both analytical continuation of the potential inside the topographic masses and truncation of a series, the latter is only the effect of analytical continuation.

    This study compares the two errors for EGM08, complete to degree 2160. The result shows that the topographic bias ranges from 0 at sea level to 5.15 m in the Himalayas region, while the DWC error ranges from -0.08 m in the Pacific to 5.30 m in the Himalayas. The zero-degree effects of the two are the same (5.3 cm), while the rms of the first degree errors are both 0.3 cm. For higher degrees the power of the topographic bias is slightly larger than that for the DWC error, and the corresponding global rms values reaches 25.6 and 25.3 cm, respectively, at nmax=2160. The largest difference (20.5 cm) was found in the Himalayas. In most cases the DWC error agrees fairly well with the topographic bias, but there is a significant difference in high mountains. The global rms difference of the two errors clearly indicates that the two series diverge, a problem most likely related with the DWC error.

  • 268.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    A study on the Fennoscandian post-glacial rebound as observed by present-day uplift rates and gravity field model GOCO02S2013In: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 48, no 3, p. 317-331Article in journal (Refereed)
    Abstract [en]

    Repeated absolute gravity measurements in Fennoscandia have revealed that the on-going post-glacial rebound can be regarded as a pure viscous flow of mantle mass of density 3390 kg/m(3) towards the central part of the region caused by a gravity/uplift rate of -0.167 mu Gal/mm. Our model estimates the rebound induced rates of changes of surface gravity and geoid height to have peaks of -1.9 mu Gal/yr and 1.6 mm/yr, respectively, the former being consistent with absolute gravity observations. The correlation coefficient of the spherical harmonic representations of the geoid height and uplift rate for the spectral windows between degrees 10 and 70 is estimated to -0.99 +/- 0.006, and the maximum remaining land uplift is estimated to the order of 80 m. Both the (almost) linear increase of relaxation time with degree and the linear relation between geoid height and uplift rate support a model with mass flow in the major part of the mantle and disqualify the model with a flow in a thin channel below the crust. The mean viscosity of the flow in the central uplift region is estimated to 4x10(21) Pa s.

  • 269.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Tenzer, Robert
    On gravity inversion by no-topography and new isostatic gravity anomalies2013Conference paper (Refereed)
  • 270.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics. University of Gävle, Sweden.
    Tenzer, Robert
    On Gravity Inversion by No-Topography and Rigorous Isostatic Gravity Anomalies2015In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136Article in journal (Refereed)
    Abstract [en]

    We discuss some theoretical aspects and practical consequences of using traditional versus “new”/rigorous formulations of the Bouguer and isostatic gravity anomalies/disturbances. In principle, the differences between these two concepts are in the definition of the so-called secondary indirect topographic effect (SITE) on the gravity data. Although we follow the tradition to call this effect SITE, we show that it is formally a direct topographic effect (DITE), needed to remove all topographic signal, but in practice not regarded as such. Consequently, there is a need for a no-topography gravity anomaly, which removes all topographic effects, leaving the below-crust Earth transparent for gravity inversion. Similarly, a rigorous isostatic gravity anomaly includes also a compensation effect for the SITE. By using a simple topographic model, we confirm a theoretically found ratio of 2/(n + 1) between the magnitudes of the SITE and DITE by wavelength (spherical harmonic degree n), both for the Bouguer and isostatic gravity anomalies. Finally, global gravity inversions are applied by utilizing the Vening Meinesz-Moritz isostatic model to determine the Moho geometry using the Bouguer gravity disturbances/anomalies and the no-topography gravity anomalies, and the results are compared. The numerical results confirm our theoretical findings that the Bouguer gravity disturbances and the no-topography gravity anomalies provide very similar results. A comparison of these gravimetrically computed Moho depths with the CRUST1.0 seismic model shows rms agreements of 4.3 and 4.5 km, respectively. This is a significant improvement when compared to the Moho result obtained by using the Bouguer gravity anomalies, yielding the rms difference of 7.3 km for the CRUST1.0 model. These results confirm a theoretical deficiency of the classical definition of the Bouguer and isostatic gravity anomalies, which do not take into consideration the SITE effects on the topography and its compensation.

  • 271.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Shirazian, Masoud
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Solving the Direct and Inverse Geodetic Problems on the Ellipsoid by Numerical Integration2012In: Journal of Surveying Engineering, ISSN 0733-9453, E-ISSN 1943-5428, Vol. 138, no 1, p. 9-16Article in journal (Refereed)
    Abstract [en]

    Taking advantage of numerical integration, we solve the direct and inverse geodetic problems on the ellipsoid. In general, the solutions are composed of a strict solution for the sphere plus a correction to the ellipsoid determined by numerical integration. Primarily the solutions are integrals along the geodesic with respect to the reduced latitude or azimuth, but these techniques either have problems when the integral passes a vertex (i.e., point with maximum/minimum latitude of the arc) or a singularity at the equator. These problems are eliminated when using Bessel's idea of integration along the geocentric angle of the great circle of an auxiliary sphere. Hence, this is the preferred method. The solutions are validated by some numerical comparisons to Vincenty's iterative formulas, showing agreements to within 2 x 10(-10) of geodesic length (or 3.1 mm) and 4 x 10(-5) as seconds of azimuth and position for baselines in the range of 19,000 km.

  • 272.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ågren, Jonas
    Investigations for the requirements of a 5 mm geoid model- a project status report2014In: NKG General Assembly 2014 Proceedings, 2014Conference paper (Refereed)
  • 273.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Local Least Squares Spectral Filtering and Combination by Harmonic Functions on the Sphere2011In: Journal of Geodetic Science, ISSN 2081-9943, Vol. 1, no 4, p. 355-360Article in journal (Refereed)
    Abstract [en]

    Least squares spectral combination is a well-known technique in physical geodesy. The established technique either suffers from the assumption of no correlations of errors between degrees or from a global optimisation of the variance or mean square error of the estimator. Today Earth gravitational models are available together with their full covariance matrices to rather high degrees, extra information that should be properly taken care of.

    Here we derive the local least squares spectral filter for a stochastic function on the sphere based on the spectral representation of the observable and its error covariance matrix. Second, the spectral combination of two erroneous harmonic series is derived based on their full covariance matrices. In both cases the transition from spectral representation of an estimator to an integral representation is demonstrated. Practical examples are given.

    Taking advantage of the full covariance matrices in the spectral combination implies a huge computational burden in determining the least squares filters and combinations for high-degree spherical harmonic series. A reasonable compromise between accuracy of estimator and workload could be to consider only one weight parameter/degree, yielding the optimum filtering and combination of Laplace series.

  • 274.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    On the Best Quadratic Minimum Bias Non-Negative Estimator of a Two-Variance Component Model2011In: Journal of Geodetic Science, ISSN 2081-9943, Vol. 1, no 3, p. 280-285Article in journal (Refereed)
    Abstract [en]

    Variance components (VCs) in linear adjustment models are usually successfully computed by unbiased estimators. However, for many unbiased VC techniques estimated variance components might be negative, a result that cannot be tolerated by the user. This is, for example, the case with the simple additive VC model aσ2/1 + bσ2/2 with known coefficients a and b, where either of the unbiasedly estimated variance components σ2/1 + σ2/2 may frequently come out negative. This fact calls for so-called non-negative VC estimators. Here the Best Quadratic Minimum Bias Non-negative Estimator (BQMBNE) of a two-variance component model is derived. A special case with independent observations is explicitly presented.

  • 275.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    On the Definition and Realization of a Global Vertical Datum2011In: Journal of Geodetic Science, ISSN 2081-9943, Vol. 1, no 2, p. 154-157Article in journal (Refereed)
    Abstract [en]

    A Global Vertical Datum (GVD) is naturally defined by the geoid, and there is a well-established consensus to adopt Gauss-Bessel-Listing's definition of the geoid (i.e. as being the level surface of the Earth's gravity field that best fits the undisturbed sea level). The main problem in defining the geoid is therefore to fix its constant geopotential (W00). Nevertheless, this definition can be interpreted as to fit either the geopotential of sea surface to a constant (W0), or to minimize the height of sea level with respect to the geoid. Although the two interpretations lead to apparently different solutions, we show that they are practically the same. To improve the estimation of W0, we propose to weight the included data according to their a priori error estimates.

    Finally we discuss the use of GNSS/levelling data for vertical datum connections, concluding that such data, although indispensable for regional vertical datum connections, in combination with satellite altimetry over the oceans are practically useless for determining the GVD. Also, such a joint adjustment of the GVD and regional vertical datum biases yields inferior local connections vs. a separate adjustment with fixed GVD.

  • 276.
    Sjöberg, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Walyeldeen, Hassan Edres
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Horemuz, Milan
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Estimation of crustal motions at the permanent GPS station SVEA, Antarctica, from 2005 to 20092011In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 1, no 3Article in journal (Refereed)
    Abstract [en]

    In November 2004 the permanent GPS station SVEA (Latitude: 74°34' 34" S, Longitude: 11° 13' 31" W, Height 1261.2 m) was installed in Drottning Maud's Land, Antarctica. The main aim of this paper is to evaluate the collected data for on-going crustal motions. About 40% ("3-days weekly") of the continuous four years GPS data from 2005 to 2009 was processed together with the simultaneous data of five IGS reference stations using Bernese GPS software V 5.0. A linear regression analysis was used to estimate the linear motion of the station, yielding the estimated velocities' components (in mm/year) of 6.6± 0.4 North, -1.4 ± 0.2 East and 4.4 ± 0.6 Up. Although all components appear highly significant, the abnormal development of the E-W component needs further analyses. Post-glacial rebound is estimated to contribute only to 0.2-0.3 mm/yr (James and Ivin, 1998) of the vertical uplift rate, suggesting that the observed vertical motion mainly has another origin, possibly tectonic. The crustal motion results should be regarded as preliminary, and they need both further data and analyses to be confirmed.

    It is also concluded that the remote continuously running GPS station SVEA works well after more than five years of operation with only annual checks and data retrieval in the harsh environment of Antarctica.

  • 277.
    Skog, Lars
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Spatial Analysis and Modeling for Health Applications2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Despite the benefits of applying methods of geographic information science (GIScience), the use of such methods in health service planning and provision remains greatly underutilized. Spread of epidemic diseases is a constant threat to mankind and the globalization of the world increases the risk for global attacks from multi-resistant bacteria or deadly virus strains. Therefore, research is needed to better understand how GIScience could be used in epidemiologic analyses and other health applications.

    This thesis is divided into two parts; one for epidemiologic analyses and one for neighbourhood studies. The overall objective of the epidemiologic part of this research is to understand more about the spatial spread of past pandemics and to find out if there are any common patterns. This overall objective is divided into four specific research objectives; 1) to describe the spatial spread of the Russian Influenza in Sweden, 2) to create models of propagation of the Black Death in Sweden, 3) to establish spatiotemporal characteristics common to past pandemics in Sweden and 4) to visualize the spatiotemporal occurrence of salmonella among animal herds in Sweden.

    This thesis also discusses some other aspects of health related to place. Are differences in neighbourhood deprivation related to the amount of presence of goods and services? Is the way cities are planned affecting the behaviour within the local population regarding spontaneous walking and physical activity? The specific research objectives for this part are to define how deprivation is related to presence of goods and services in Sweden and to create walkability indices over the city of Stockholm including a quality test of these indices.

    Case data reported by physicians were used for the epidemiologic studies. The pandemics discussed covered the entire world, but our data is from Sweden only and as regards the Black Death there was no case data at all. The data for the goods and services analyses are from all of Sweden, whereas the walkability indices are based on data from the city of Stockholm. Various methods have been used to clean, structure and geocode the data, including hand written reports on case data, maps of poor geometric quality, information from databases on climate, demography, diseases, goods and services, income data and more, to make this data feasible for spatial analysis, modeling and visualization. Network analysis was used to model food transports in the 14th century as well as walking in the city of Stockholm today. Proximity analysis was used to assess the spatio-temporal spread of the Russian Influenza. The impact of climatological factors on the propagation of the Asian Influenza was analyzed and geographically weighted mean (GWM) calculations were used to discover common characteristics in the spatio-temporal spread of three past pandemics.

    Among the results generated in the epidemiologic study the following should be noted in particular; the local peaking periods of the Asian Influenza were preceded by falling temperature, the total peaking period for the three pandemics (Russian, Asian and A(H1N1)pdm09) was approximately 10 weeks and their weekly GWM followed a path from southwest to northeast (opposite direction for the A(H1N1)pdm09). From the neighborhood studies one can note that compared to the results measured and reported by tested individuals there is a positive (small but significant) association between neighborhood walkability and physical activity outcomes.

    The main contribution of this work is that it gives epidemiologists and public health specialists new ideas, not only on how to formulate, model, analyze and visualize different health related research questions but also ideas on how new procedures could be implemented in their daily work. Once the data reporting is organized in a suitable manner there is a multitude of options on how to present important and critical information to officials and policy makers.

  • 278.
    Skog, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Hauska, Hans
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Spatial Modeling of the Black Death in Sweden2013In: Transactions on GIS, ISSN 1361-1682, E-ISSN 1467-9671, Vol. 17, no 4, p. 589-611Article in journal (Refereed)
    Abstract [en]

    The purpose of this work is to determine whether spatial modeling can be used to model the spread of the Black Death. The study is limited to models for the propagation of the disease in Sweden in 1350. Geographic data of Swedish water bodies and medieval road networks, historical data on the population in Swedish parishes, including their medieval boundaries, along with historical notes and disease characteristics, were used to build alternative models for spatial distribution. Three different models are presented: one radial, one cost-based and one combining network analysis and radial propagation. Simulations were made to depict different scenarios on the spread of the disease, as well as the drastic changes in the overall population of Sweden, over a couple of hundred years. For purpose of validation the population decrease estimated in each parish is compared with independent historical documents. Results from model scenarios are visualized in maps of propagation, animated video sequences and a web map service. Our analyses clearly demonstrate the power of spatial analysis and geographic information systems to describe, model and visualize epidemiologic processes in space and time.

  • 279.
    Skog, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Hauska, Hans
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Linde, Annika
    Swedish Institute for Infectious Disease Control.
    The Russian influenza in Sweden in 1889-90: an example of Geographic Information System analysis2008In: Euro surveillance : bulletin Européen sur les maladies transmissibles = European communicable disease bulletin, ISSN 1560-7917, Vol. 13, no 49Article in journal (Refereed)
    Abstract [en]

    Using data from a study of the 1889-90 Russian flu in Sweden, this article describes how the application of Geographic Information System (GIS) may improve analyses and presentation of surveillance data. In 1890, immediately after the outbreak, all Swedish doctors were asked to provide information about the start and the peak of the epidemic, and the total number of cases in their region and to fill in a questionnaire on the number, sex and age of infected persons in the households they visited. General answers on the epidemic were received from 398 physicians and data on individual patients were available for more than 32,600 persons. These historic data were reanalysed with the use of GIS, in map documents and in animated video sequences, to depict the onset, the intensity and the spread of the disease over time. A stack diagram with the observations grouped into one week intervals was produced to depict the spread in one figure only. To better understand how the influenza was disseminated, Thiessen polygons were created around 70 places reported on by the doctors. Having prepared GIS layers of the population (divided into parishes), estimations could be made for all the Swedish parishes on the number of infected persons for each of the 15 weeks studied. The described models may be useful in current epidemiological investigations, as well.

  • 280.
    Skog, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Linde, Annika
    Palmgren, Helena
    Hauska, Hans
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Elgh, Fredrik
    Spatiotemporal characteristics of pandemic influenza2014In: BMC Infectious Diseases, ISSN 1471-2334, E-ISSN 1471-2334, Vol. 14, no 1, p. 378-Article in journal (Refereed)
    Abstract [en]

    Background: Prediction of timing for the onset and peak of an influenza pandemic is of vital importance for preventive measures. In order to identify common spatiotemporal patterns and climate influences for pandemics in Sweden we have studied the propagation in space and time of A(H1N1)pdm09 (10,000 laboratory verified cases), the Asian Influenza 1957-1958 (275,000 cases of influenza-like illness (ILI), reported by local physicians) and the Russian Influenza 1889-1890 (32,600 ILI cases reported by physicians shortly after the end of the outbreak). Methods: All cases were geocoded and analysed in space and time. Animated video sequences, showing weekly incidence per municipality and its geographically weighted mean (GWM), were created to depict and compare the spread of the pandemics. Daily data from 1957-1958 on temperature and precipitation from 39 weather stations were collected and analysed with the case data to examine possible climatological effects on the influenza dissemination. Results: The epidemic period lasted 11 weeks for the Russian Influenza, 10 weeks for the Asian Influenza and 9 weeks for the A(H1N1)pdm09. The Russian Influenza arrived in Sweden during the winter and was immediately disseminated, while both the Asian Influenza and the A(H1N1)pdm09 arrived during the spring. They were seeded over the country during the summer, but did not peak until October-November. The weekly GWM of the incidence moved along a line from southwest to northeast for the Russian and Asian Influenza but northeast to southwest for the A(H1N1)pdm09. The local epidemic periods of the Asian Influenza were preceded by falling temperature in all but one of the locations analysed. Conclusions: The power of spatiotemporal analysis and modeling for pandemic spread was clearly demonstrated. The epidemic period lasted approximately 10 weeks for all pandemics. None of the pandemics had its epidemic period before late autumn. The epidemic period of the Asian Influenza was preceded by falling temperatures. Climate influences on pandemic spread seem important and should be further investigated.

  • 281.
    Skog, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Linde, Annika
    Swedish Institute for Communicable Disease Control.
    Palmgren, Helena
    Clinical Microbiology, Umeå University.
    Hauska, Hans
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Elgh, Fredrik
    Clinical Microbiology, Umeå University.
    Spatiotemporal charactyeristics of pandemic influenzaManuscript (preprint) (Other academic)
  • 282.
    Skrifvare, Ann-Mari
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Change Detection in Stockholm between 1986 and 2006 using SPOT Multispectral and Panchromatic Data2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With an increasing urban population in Sweden, expecting to reach 90% by 2050 (UN World Urbanization prospects, The 2011 Revision), this high level of urban population put pressure on functioning infrastructure, sufficient housing and need to monitor the environmental effects such as pollution and the effects of land use change. Stockholm County currently holds 22% of the population and accounts for nearly half of the urban growth in Sweden (Svensk Handelskammare).  

    Previous research on change detection using remote sensing cover the use of data sets from optical sensors, infrared spectrum, radar data and the use of additional derived data sets such as indices and texture measure (implemented on pixel or feature level). There is not yet any consensus regarding which change detection methods that is superior to others. Comparative studies often only test a few algorithms on one particular data set. Change detection of Stockholm urban area has not been well investigated in previous literature.

    This thesis is focused on a change detection analysis of Stockholm area between 1986 and 2006 using remote sensing data fusion. The data set used is SPOT-1 HRV XS data at 20m resolution from 1986, SPOT-1 HRV Panchromatic data at 10m resolution from 1987 and SPOT-5 HRG XS data of 10m resolution from 2006.

    The first challenge was to fuse the multispectral and panchromatic images from 1986 and 1987 to inject the details of the 10m panchromatic image into the 20m multispectral so that the resulting images will have similar spatial details as the 2006 images. This was done by wavelet transform. Haar, Daubechies, Coiflet and Biorthogonal wavelet families were tested to find the optimal fusion and the corresponding parameters. The results showed that the Daubechies, Coiflet and Biorthogonal families did not differ significantly and that for this data set and analysis purpose more than one wavelet family fusion results showed satisfactory results. The correlation coefficient for these three families was all over 0,96 at decomposition level two.  

    Then change detection was performed using change vector analysis (CVA) and a supervised non-parametric classifier. A comparison is made between two inputs: one using only spectral information and the other adding textural information to the spectral information. The change detection analysis was undertaken in three steps: calculating texture measures from the original images, calculating change magnitude using Change Vector Analysis (CVA) and classifying change from no-change using Support Vector Machine (SVM).

    Three GLCM texture measures were chosen: Homogeneity, Mean and Entropy in the change detection analysis. These, as well as the spectral information, were input for change vector magnitude. Then SVM is used to classify changed pixels from no-change pixels. Two change results were obtained, the first using only spectral information, and the other using both spectral and textural information.

    The overall accuracy using only spectral information was rather high at 87, 86%. But the visual inspections indicate that using only spectral change magnitude is not sufficient for a good change detection result because there is an apparent overestimation of change. When adding the textural information the overall accuracy increase drastically to 97,01%, although at visual inspection there seem to be an underestimation of change.  Because of the high overall accuracy an independent validation was made causing the overall accuracy and kappa to decrease. Change detection using only multispectral data got an overall accuracy of 76, 12% and kappa coefficient 0,53. For change detection result with added texture measures the overall accuracy became 85,80%  and 0,72.  The results further confirm the general advantages using texture measure although the independent evaluation resulted in a lower accuracy than the author's evaluations.

  • 283. Ssengendo, Ronald
    et al.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Gidudu, A.
    Evaluation of EGM08 in Uganda: Preliminary Results2011In: The first Conference on Advances in Geomatics Research, 2011, p. 195-201Conference paper (Refereed)
    Abstract [en]

    his paper presents an overview of the preliminary evaluation results of the new Earth Gravitational Model (EGM08) in Uganda. The evaluation was based on a network of 12 GNSS/levelling points in Kampala and was performed in point wise (absolute) and relative (varying baselines) sense. For completeness the evaluation tests were also performed for EGM96. Our preliminary results were inconclusive as in the absolute tests, EGM96 was unexpectedly significantly better than EGM08. However, in the relative tests, EGM08 was consistently better than EGM96 for all baseline lengths considered. Subsequently further tests with much higher density and distribution than our test network should be carried out to conclusively determine the best global model for geodetic applications in Uganda.

  • 284. Sundquist, Kristina
    et al.
    Eriksson, Ulf
    Kawakami, Naomi
    Skog, Lars
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ohlsson, Henrik
    Arvidsson, Daniel
    Neighborhood walkability, physical activity, and walking behavior: The Swedish Neighborhood and Physical Activity (SNAP) study2011In: Social Science and Medicine, ISSN 0277-9536, E-ISSN 1873-5347, Vol. 72, no 8, p. 1266-1273Article in journal (Refereed)
    Abstract [en]

    More knowledge concerning the association between physical activity and objectively measured attributes of the built environment is needed. Previous studies on the association between objectively measured neighborhood walkability, physical activity, and walking have been conducted in the U.S. or Australia and research findings are available from only one country in Europe - Belgium. The first aim of this Swedish study of 2269 adults was to examine the associations between neighborhood walkability and walking for active transportation or leisure, and moderate-to-vigorous physical activity (MVPA) and whether these hypothesized associations are moderated by age, gender, income, marital status and neighborhood-level socioeconomic status. The second aim was to determine how much of the total variance of the walking and physical activity outcomes can be attributed to neighborhood-level differences. Neighborhood walkability was objectively measured by GIS methods. An index consisting of residential density, street connectivity, and land use mix was constructed to define 32 highly and less walkable neighborhoods in Stockholm City. MVPA was measured objectively during 7 days with an accelerometer and walking was assessed using the validated International Physical Activity Questionnaire (IPAQ). Multilevel linear as well as logistic models (mixed-effects, mixed-distribution models) were used in the analysis. The statistically significant and "adjusted" results for individuals living in highly walkable neighborhoods, as compared to those living in less walkable neighborhoods, were: (1) 77% and 28% higher odds for walking for active transportation and walking for leisure, respectively, (2) 50 min more walking for active transportation/week, and (3) 3.1 min more MVPA/day. The proportion of the total variance at the neighborhood level was low and ranged between 0.0% and 2.1% in the adjusted models. The findings of the present study stress that future policies concerning the built environment must be based on context-specific evidence, particularly in the light of the fact that neighborhood redevelopments are time-consuming and expensive.

  • 285.
    Susilo, Yusak Octavius
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics.
    Prelipcean, Adrian Corneliu
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Gidofalvi, Gyözö
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Allström, Andreas
    Sweco.
    Kristoffersson, Ida
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Widell, Jenny
    Sweco.
    Lessons from a trial of MEILI, a smartphone based semi-automatic activity-travel diary collector, in Stockholm city, SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    This paper describes the lessons learned from the trial of MEILI, a smartphone based semi-automatic activity-travel diarycollection system, in Stockholm city, Sweden. The design of the system, together with state-of-the-art improvements of different elements of the tool, are presented before and after the trial to better illustrate the improvements based on the lessons learned. During the trial, both MEILI and a paper-based diary captured about 65% of the total number of detected trips, but only about half of the trips were captured by both systems. The unmatchable trips are partly due to different activity declaration and system specific destination specification, i.e., a verbose specification of address in the paper-and-pencil survey and a point of interest selection / declaration in MEILI. In terms of subjective appreciation, the user experiences vary greatly between the different participants in the pilot. Presumably, this is mainly due to different level of IT-knowledge of the respondents, but also due to the occasionally non-uniform behaviour of the location collection service caused by hardware and / or software difficulties. Based on these inputs, further web and support system improvements have been implemented for future trials.

  • 286.
    Tao, Jia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bin, Jiang
    University of Gävle.
    Exploring Human Activity Patterns Using Taxicab Static Points2012In: ISPRS International Journal of Geo-Information, ISSN 2220-9964, Vol. 1, no 1, p. 89-107Article in journal (Refereed)
    Abstract [en]

    This paper explores the patterns of human activities within a geographical space by adopting the taxicab static points which refer to the locations with zero speed along the tracking trajectory. We report the findings from both aggregated and individual aspects. Results from the aggregated level indicate the following: (1) Human activities exhibit an obvious regularity in time, for example, there is a burst of activity during weekend nights and a lull during the week. (2) They show a remarkable spatial drifting pattern, which strengthens our understanding of the activities in any given place. (3) Activities are heterogeneous in space irrespective of their drifting with time. These aggregated results not only help in city planning, but also facilitate traffic control and management. On the other hand, investigations on an individual level suggest that (4) activities witnessed by one taxicab will have different temporal regularity to another, and (5) each regularity implies a high level of prediction with low entropy by applying the Lempel-Ziv algorithm.

  • 287.
    Tao, Jia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bin, Jiang
    University of Gävle.
    Measuring Urban Sprawl Based on Massive Street Nodes and the Novel Concept of Natural CitiesManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, we develop a novel approach to measuring urban sprawl based on street nodes and naturallydefined urban boundaries, both extracted from massive volunteered geographic informationOpenStreetMap databases through some data-intensive computing processes. The street nodes are definedas street intersections and ends, while the naturally defined urban boundaries constitute what we callnatural cities. We find that the street nodes are significantly correlated with population of cities. Based onthis finding, we set street nodes as a proxy of population to measure urban sprawl. We further find thatstreet nodes bear a significant linear relationship with city areal extents. In the plot with the x axisrepresenting city areal extents, and the y axis street nodes, sprawling cities are located below the regressionline. We verified the approach using urban areas and population from the US census, and then applied theapproach to three European countries: France, Germany, and the United Kingdom for the categorization ofnatural cities into three classes: sprawling, compact, and normal. This categorization sets a uniformstandard for cross comparing sprawling levels across an entire country.

  • 288.
    Tao, Jia
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Bin, Jiang
    University of Gävle.
    Scaling property of urban system using an entropy-based hierarchical clustering method2012In: Proceedings of the AGILE'2012 / [ed] Jérôme Gensel, Didier Josselin and Danny Vandenbroucke, 2012Conference paper (Refereed)
    Abstract [en]

    Urban systems have long been characterized as the scaling property, although there are a lot of argues on the definition and organization of its component or spatial unit. In this paper we propose an entropy-based hierarchical clustering method to aggregate the individual location to form the component or spatial unit. Through the application of the method to three datasets from the different aspects of urban systems, we double check the robustness and consistence of this method. Importantly, it is found that the size of the derived component or spatial unit follows a remarkably power law distribution, which further suggests the scaling property of the underlying urban systems.

  • 289. Tenzer, R.
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Reference crust-mantle density contrast beneath Antarctica based on the Vening Meinesz-Moritz isostatic inverse problem and CRUST2.0 seismic model2013In: Earth Sciences Research Journal, ISSN 1794-6190, E-ISSN 2339-3459, Vol. 17, no 1, p. 7-12Article in journal (Refereed)
    Abstract [en]

    The crust-mantle (Moho) density contrast beneath Antarctica was estimated based on solving the Vening Meinesz-Moritz isostatic problem and using constraining information from a seismic global crustal model (CRUST2.0). The solution was found by applying a least-squares adjustment by elements method. Global geopotential model (GOCO02S), global topographic/bathymetric model (DTM2006.0), ice-thickness data for Antarctica (assembled by the BEDMAP project) and global crustal model (CRUST2.0) were used for computing isostatic gravity anomalies. Since CRUST2.0 data for crustal structures under Antarctica are not accurate (due to a lack of seismic data in this part of the world), Moho density contrast was determined relative to a reference homogenous crustal model having 2,670 kg/m3 constant density. Estimated values of Moho density contrast were between 160 and 682 kg/m3. The spatial distribution of Moho density contrast resembled major features of the Antarctic's continental and surrounding oceanic tectonic plate configuration; maxima exceeding 500 kg/m3 were found throughout the central part of East Antarctica, with an extension beneath the Transantarctic mountain range. Moho density contrast in West Antarctica decreased to 400-500 kg/m3, except for local maxima up to ~ 550 kg/m3 in the central Antarctic Peninsula.

  • 290. Tenzer, R.
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Hwang, C.
    Chang, E. T. -Y
    Moho interface modeling beneath the himalayas, tibet and central siberia using GOCO02S and DTM2006.02013In: Terrestrial, Atmospheric and Oceanic Science, ISSN 1017-0839, E-ISSN 2223-8964, Vol. 24, no 4 PART1, p. 581-590Article in journal (Refereed)
    Abstract [en]

    We apply a newly developed method to estimate the Moho depths and density contrast beneath the Himalayas, Tibet and Central Siberia. This method utilizes the combined least-squares approach based on solving the inverse problem of isostasy and using the constraining information from the seismic global crustal model (CRUST2.0). The gravimetric forward modeling is applied to compute the isostatic gravity anomalies using the global geopotential model (GOCO02S) and the global topographic/ bathymetric model (DTM2006.0). The estimated Moho depths vary between 60 - 70 km beneath most of the Himalayas and Tibet and reach the maxima of ~79 km. The Moho depth under Central Siberia is typically 50 - 60 km. The Moho density contrast computed relative to the CRUST2.0 lower crustal densities has the maxima of ~300 kg m-3 under Central Tibet. It substantially decreases to 150 - 250 kg m-3 under Himalayas and north Tibet. The estimated Moho density contrast under central Siberia is within 100 - 200 kg m-3.

  • 291. Tenzer, R.
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Vajda, P.
    Depth-dependent density change within the continental upper mantle2012In: Contributions to Geophysics and Geodesy, ISSN 1335-2806, Vol. 42, no 1, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The empirical model of the depth-dependent density change within the upper continental mantle is derived in this study. The density of the upper(most) mantle underlying the continental crust is obtained from the estimated values of the crust-mantle (Moho) density contrast. Since the continental crustal thickness varies significantly, these upper mantle density values to a large extent reflect the density changes with depth. The estimation of the Moho density contrast is done through solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy. The solution combines gravity and seismic data in the least-squares estimation model. The estimated upper mantle density (beneath the continental crust) varies between 2770 and 3649 kg/m 3. The upper mantle density increases almost proportionally with depth at a rate of 13 ± 2 kg/m 3 per 1 km at the investigated depth interval from 6 to 58 km.

  • 292. Tenzer, Robert
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Gladkikh, Vladislav
    Signature of the upper mantle density structure in the refined gravity data2012In: Computational Geosciences, ISSN 1420-0597, E-ISSN 1573-1499, Vol. 16, no 4, p. 975-986Article in journal (Refereed)
    Abstract [en]

    The gravitational signal of the upper mantle density structures is investigated in the refined gravity data which are corrected for the gravitational contributions of the crust density structures and the Moho geometry. The gravimetric forward modeling is applied to compute these refined gravity data globally on a 1 x 1 arcdeg grid using the global geopotential model (EGM2008), the global topographic/bathymetric model (DTM2006.0) including the ice-thickness data, and the global crustal model (CRUST2.0). The characteristics of the upper mantle density structures are further analyzed in association with the Moho parameters (i.e., Moho depths and density contrast). The 1 x 1 arcdeg global data of the Moho parameters are estimated by applying the combined least-squares approach based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy. The refined gravity data exhibit mainly the mantle lithosphere structures attributed to the global mantle convection. A significant correlation found over oceans between the refined gravity data and the Moho density contrast is explained by the increasing density of the oceanic lithosphere with age. Despite the lithosphere structures attributed to the global mantle convection are confirmed also in the refined gravity data over continents, the significant correlation between the refined gravity data and the Moho parameters is in this case absent. Instead, the significant proportion of lateral variations of the Moho density contrast within the continental lithosphere is attributed to the depth-dependant density changes due to pressure and thermal gradient.

  • 293. Tenzer, Robert
    et al.
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Vajda, Peter
    Global model of the upper mantle lateral density structure based on combining seismic and isostatic models2013In: Geosciences Journal, ISSN 1226-4806, Vol. 17, no 1, p. 65-73Article in journal (Refereed)
    Abstract [en]

    We compile the global model of the upper mantle lateral density structure with a 2x2 arc-deg spatial resolution using the values of the crust-mantle density contrast estimated relative to the adopted crust density model. The combined least-squares approach based on solving Moritz's generalization of the Vening-Meinesz inverse problem of isostasy is facilitated to estimate the crust-mantle density contrast. The global geopotential model (EGM08), the global topographic/bathymetric model (DTM2006.0) including ice-thickness data, and the global crustal model (CRUST2.0) are used to compute the isostatic gravity anomalies. The estimated upper mantle densities globally vary between 2751 and 3635 kg/m(3). The minima correspond with locations of the divergent oceanic tectonic plate boundaries (along the mid-oceanic ridges). The maxima are found along the convergent tectonic plate boundaries in the Andes and Himalayas (extending under the Tibetan Plateau). A comparison of the estimated upper mantle densities with the CRUST2.0 data shows a relatively good agreement between these two models within the continental lithosphere with the differences typically within +/- 100 kg/m(3). Much larger discrepancies found within the oceanic lithosphere are explained by the overestimated values of the CRUST2.0 upper mantle densities. Our result shows a prevailing pattern of increasing densities with the age of oceanic lithosphere which is associated with the global mantle convection process.

  • 294. Tenzer, Robert
    et al.
    Chen, Wenjin
    Tsoulis, Dimitrios
    Bagherbandi, Mohammad
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Novak, Pavel
    Jin, Shuanggen
    Analysis of the Refined CRUST1.0 Crustal Model and its Gravity Field2015In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 36, no 1, p. 139-165Article, review/survey (Refereed)
    Abstract [en]

    The global crustal model CRUST1.0 (refined using additional global datasets of the solid topography, polar ice sheets and geoid) is used in this study to estimate the average densities of major crustal structures. We further use this refined model to compile the gravity field quantities generated by the Earth's crustal structures and to investigate their spatial and spectral characteristics and their correlation with the crustal geometry in context of the gravimetric Moho determination. The analysis shows that the average crustal density is 2,830 kg/m(3), while it decreases to 2,490 kg/m(3) when including the seawater. The average density of the oceanic crust (without the seawater) is 2,860 kg/m(3), and the average continental crustal density (including the continental shelves) is 2,790 kg/m(3). The correlation analysis reveals that the gravity field corrected for major known anomalous crustal density structures has a maximum (absolute) correlation with the Moho geometry. The Moho signature in these gravity data is seen mainly at the long-to-medium wavelengths. At higher frequencies, the Moho signature is weakening due to a noise in gravity data, which is mainly attributed to crustal model uncertainties. The Moho determination thus requires a combination of gravity and seismic data. In global studies, gravimetric methods can help improving seismic results, because (1) large parts of the world are not yet sufficiently covered by seismic surveys and (2) global gravity models have a relatively high accuracy and resolution. In regional and local studies, the gravimetric Moho determination requires either a detailed crustal density model or seismic data (for a combined gravity and seismic data inversion). We also demonstrate that the Earth's long-wavelength gravity spectrum comprises not only the gravitational signal of deep mantle heterogeneities (including the core-mantle boundary zone), but also shallow crustal structures. Consequently, the application of spectral filtering in the gravimetric Moho determination will remove not only the gravitational signal of (unknown) mantle heterogeneities, but also the Moho signature at the long-wavelength gravity spectrum.

  • 295.
    Uggla, Gustaf
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ekblad, Jacob
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Geodatasamverkan: Geospatial infrastruktur i Sverige2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract

    In order to comply with the directives regarding distribution of geographic information given by the European Union (EU), Sweden has implemented an interaction model called Geodatasamverkan. This model regulates how authorities and municipalities distribute and use geographic information. The purpose behind Geodatasamverkan is to increase the availability and encourage the use of geographic information.

    The purpose of this study is to investigate why the majority of Swedish municipalities have chosen not to be a part of Geodatasamverkan and to present areas for improvement within Geodatasamverkan. The study was conducted through questionnaires sent to all Swedish municipalities and also interviews with a few chosen municipalities. The questions have covered the municipalities’ expectations and experiences regarding Geodatasamverkan.

    The study led us to the conclusions that the participation in Geodatasamverkan is lower among the smaller municipalities and that they believe their fees are unproportionally high. A lot of the smaller municipalities work together in questions regarding geographic information due to a lack of resources. They would like the option to participate in Geodatasamverkan in such constellations at a reduced fee.

    Almost all municipalities, regardless of size and population, agrees there is a noticeable potential for improvement within each municipality. This would increase the benefits of Geodatasamverkan without changing Geodatasamverkan itself. Examples of these improvements include education and improved working practices.

  • 296. Wang, Jiechen
    et al.
    Cui, Can
    Rui, Yikang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Cheng, Liang
    Pu, Yingxia
    Wu, Wenzhou
    Yuan, Zhenyu
    A parallel algorithm for constructing Voronoi diagrams based on point-set adaptive grouping2014In: Concurrency and Computation, ISSN 1532-0626, E-ISSN 1532-0634, Vol. 26, no 2, p. 434-446Article in journal (Refereed)
    Abstract [en]

    This paper presents a parallel algorithm for constructing Voronoi diagrams based on point-set adaptive grouping. The binary tree splitting method is used to adaptively group the point set in the plane and construct sub-Voronoi diagrams for each group. Given that the construction of Voronoi diagrams in each group consumes the majority of time and that construction within one group does not affect that in other groups, the use of a parallel algorithm is suitable.After constructing the sub-Voronoi diagrams, we extracted the boundary points of the four sides of each sub-group and used to construct boundary site Voronoi diagrams. Finally, the sub-Voronoi diagrams containing each boundary point are merged with the corresponding boundary site Voronoi diagrams. This produces the desired Voronoi diagram. Experiments demonstrate the efficiency of this parallel algorithm, and its time complexity is calculated as a function of the size of the point set, the number of processors, the average number of points in each block, and the number of boundary points.

  • 297.
    Wohletz, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    A GIS Model to Estimate a Sustainable Potential of Forest Fuel for Energy Generation in the Municipality of Växjö, Sweden2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Since the 1980s the municipality of Växjö in Southern Sweden has been increasingly focusing on using wood to produce energy for the region. A permanent and sustainable supply of wood material is therefore indispensable. The main source for this wood fuel is harvested wood from forests which can be used as energy, so-called forest fuel. The objective of this research is to develop a model to estimate a sustainable potential of forest fuel supply until the year 2050 for the municipality using a geographic information system (GIS). The model overall follows a top-down approach that consists of three sequential modeling steps which are generally applicable for biomass potential estimations: a theoretical, technical and the reduced technical potential. For input data the model uses georeferenced forest data (called kNN-Sweden) and topographic data about the study area to describe and narrow down the forest fuel potential by setting numerical or topographic (spatial) parameters for each modeling step. In this report forest data from 2005 has been used, which was obtained shortly before the storm ‘Gudrun’ hit and damaged great parts of the Swedish forest landscape. This factor might have resulted in slightly misleading estimated numerical modeling results concerning the actual future forest fuel supplies, but is not related to the overall layout of the model. The results show that the municipality of Växjö should be able to satisfy its demand for energy wood from harvested forest wood alone until around the year 2035, but might have shortages after that year until 2050 (and possibly beyond that). This thesis concludes that for the next 40 years the municipality of Växjö should not only rely on its annually available forest fuel capacity, but instead, different wood resources, such as recycled wood from constructions or furniture, have to be utilized or forest wood from years with surplus supply have to be stored for future tighter years. For more accurate results the modeling steps should be repeated with more recent forest data. The report also concludes that the estimation of the forest fuel potential in this study still lacks accuracy and that it is advised to treat the estimated numerical modeling results with caution. There’s still room for further improvement, and therefore possible error sources and suggestions for future work are listed.

  • 298. Wu, Z.
    et al.
    Cao, J.
    Mao, Bo
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Wang, Y.
    Semi-SAD: Applying semi-supervised learning to shilling attack detection2011In: RecSys - Proc. ACM Conf. Recomm. Syst., 2011, p. 289-292Conference paper (Refereed)
    Abstract [en]

    Collaborative filtering (CF) based recommender systems are vulnerable to shilling attacks. In some leading e-commerce sites, there exists a large number of unlabeled users, and it is expensive to obtain their identities. Existing research efforts on shilling attack detection fail to exploit these unlabeled users. In this article, Semi-SAD, a new semi-supervised learning based shilling attack detection algorithm is proposed. Semi-SAD is trained with the labeled and unlabeled user profiles using the combination of naïve Bayes classifier and EM-λ, augmented Expectation Maximization (EM). Experiments on MovieLens datasets show that our proposed Semi-SAD is efficient and effective.

  • 299. Wu, Z.
    et al.
    Mao, Bo
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Cao, J.
    MRGIR: Open geographical information retrieval using MapReduce2011In: Proc. - Int. Conf. Geoinformatics, Geoinformatics, 2011Conference paper (Refereed)
    Abstract [en]

    City objects recommendation based on characteristics of users, location, time and weather is a challenging issue in geographical information retrieval (GIR). In the meanwhile, city objects recommendation is a computation-intensive and data-intensive application. Cloud computing has gained significant attention in recent years to process the large volume of data. MapReduce framework is currently a most dominant technology in cloud computing. Augmented User-based Collaborative Filtering (AUCF) algorithm which can effective deal with hybrid variable types is proposed firstly. Then, MapReduce for GIR (MRGIR) is presented and AUCF is implemented within MRGIR as an example. The MRGIR is implemented in Hadoop which is an open source framework for MapReduce. Experimental results shows that with moderate number of map tasks, the execution time of GIR algorithms (i.e., AUCF) can be reduced remarkably.

  • 300.
    Xintao, Liu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Ban, Yifang
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Uncovering urban mobility patterns with massive floating car dataIn: Computers, Environment and Urban Systems, ISSN 0198-9715, E-ISSN 1873-7587Article in journal (Other academic)
    Abstract [en]

    Urban mobility patterns are crucial to understanding urban structures, with applications ranging from traffic forecasting to urban planning. This paper develops a bottom-up approach to assess urban mobility patterns in a quantitative manner based on over 14,200,000 GPS points obtained from 11,263 moving taxicabs in Wuhan, Hubei, China. These taxicabs are equipped with GPS devices and are continuously being driven; thus, the corresponding mobile data sets (i.e., floating car data) cover the entire urban open space and bear traffic characteristics. Consequently, such mobile data are unique and more suitable for urban mobility analysis. Instead of employing the commonly used trajectory methods, we divided the GPS points into moves and stops, focusing on the latter. We found that the time intervals for all of the stops demonstrate the scaling property; that is, the stops can be separated into far more short ones than long ones, which we believe to be typical of the traffic system. The long stops showed a cluster pattern in a self-organized way at different timelines. We extracted these spatiotemporal clusters in a natural way and found that their sizes bear a heavy-tailed distribution. We further analyzed their evolution in both time and space and then categorized them into hotspots and traffic jams, of which the distributions objectively and quantitatively suggest the dynamic and multiple nuclei of urban mobility patterns. This study also provides insights into research on mobile data from the perspective of a complex system.

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