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  • 1.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
    A Strategy for Optimum Designing of the Geodetic Networks from the Cost, Reliability and Precision Views2007In: Acta Geodaetica et Geophysica Hungarica, ISSN 1217-8977, E-ISSN 1587-1037, Vol. 42, no 3, p. 297-308Article in journal (Refereed)
    Abstract [en]

    There are different criteria for designing a geodetic network in an optimal way. An optimum network can be regarded as a network having high precision, reliability and low cost. Accordingly, corresponding to these criteria different single-objective models can be defined. Each one can be subjected to two other criteria as constraints. Sometimes the constraints can be contradictory so that some of the constraints are violated. In this contribution, these models are mathematically reviewed. It is numerically shown how to prepare these mathematical models for optimization process through a simulated network. We found that the reliability model yields small position changes between those obtained using precision respectively. Elimination of some observations may happen using precision and cost model while the reliability model tries to save number of observations. In our numerical studies, no contradictions can be seen in reliability model and this model seems to be more suitable for designing of the geodetic and deformation networks.

  • 2.
    Eshagh, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Kiamehr, Ramin
    Evaluating of robust techniques in suppressing the impact of outliers in a deformation monitoring network: A case study on the Teheran Milad tower network2007In: Acta Geodaetica et Geophysica Hungaria, ISSN 1217-8977, Vol. 42, no 4, p. 449-463Article in journal (Refereed)
    Abstract [en]

    The problem of handling outliers in a deformation monitoring network is of special importance, because the existence of outliers may lead to false deformation parameters. One of the approaches to detect the outliers is to use robust estimators. In this case the network points are computed by such a robust method, implying that the adjustment result is resisting systematic observation errors, and, in particular, it is insensitive to gross errors and even blunders. Since there are different approaches to robust estimation, the resulting estimated networks may differ. In this article, different robust estimation methods, such as the M-estimation of Huber, the "Danish", and the L-1-norm estimation methods, are reviewed and compared with the standard least squares method to view their potentials to detect outliers in the Tehran Milad tower deformation network. The numerical studies show that the L-1-norm is able to detect and down-weight the outliers best, so it is selected as the favourable approach, but there is a lack of uniqueness. For comparison, Baarda's method "data snooping" can achieve similar results when the outlier magnitude of an outlier is large enough to be detected; but robust methods are faster than the sequential data snooping process.

  • 3.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    A new height datum for Iran based on combination of the Gravimetric and GPS/levelling geoid models2005Conference paper (Other academic)
  • 4.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    A new height datum for Iran based on combination of the Gravimetric and GPS/levelling geoid models2007In: Acta Geodaetica et Geophysica, ISSN 1217-8977, Vol. 42, no 1, p. 69-81Article in journal (Refereed)
    Abstract [en]

    A new geoid model for Iran (IRG04) was computed based on the least squares modification of the Stokes formula. IRG04 was derived from the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM) and GRACE GGM02 global geopotential model. In order to define a new height datum for Iran, we attempted to combine this high resolution gravimetric geoid model with GPS/levelling data using the corrective surface approach. The corrective surface was constructed from 224 GPS/levelling points and then evaluated with 35 independent points. Different interpolation techniques were tested for the creation of the corrective surface; among them the Kriging method was selected as it gave the smallest RMS and 'noise level' at the comparisons with GPS/levelling data. The RMS fit of the new combined geoid model versus the independent GPS/levelling data is 0.09 m, it is near four times better compared to the original gravimetric geoid model. The combined model should be more convenient and useful in definition of the new height reference surface, specifically in engineering and GPS/levelling projects.

  • 5.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    A new height datum for Iran based on the combination of the gravimetric and geometric geoid models2007In: Dynamic Planet: Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools / [ed] Tregoning, P; Rizos, C, 2007, Vol. 130, p. 480-487Conference paper (Refereed)
    Abstract [en]

    A new geoid model for Iran (IRG04) is computed based on the method of least squares modification of Stokes formula based on the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM) and GRACE GGM02 Global Geopotential Model. In order to define a new height datum for Iran, we attempt to combine this high resolution gravimetric geoid model with GPS/levelling data by using a corrective surface idea. The corrective surface is constructed based on 224 GPS/levelling points and then evaluated with 35 independent points. Different interpolation techniques were tested for the creation of the corrective surface; among them the Kriging method gives the minimum RMS and noise level versus the suggesting that GPS/levelling data. The RMS of fitting the new combined geoid model versus GPS/levelling data is 0.09 in, it is near 4 times better accuracy compared with the original gravimetric geoid model. Comparing the later model, the new surface should be more convenient and useful in definition of the new height datum, specifically in engineering and GPS/levelling projects.

  • 6.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    A strategy for determining the regional geoid in developing countries by combining limited ground data with satellite-based global geopotential and topographical models: A case study of Iran2006In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, J. Geodesy, Vol. 79, no 10,11, p. 602–612-Article in journal (Refereed)
    Abstract [en]

    The computation of regional gravimetric geoid models with reasonable accuracy, in developing countries, with sparse data is a difficult task that needs great care. Here we investigate the procedure for gathering, evaluating and combining different data for the determination of a gravimetric geoid model for Iran, where limited ground gravity data are available. Heterogeneous data, including gravity anomalies, the high-resolution Shuttle Radar Topography Mission global digital terrain model and different global geopotential models including recently published Gravity Recovery and Climate Experiment models, are combined through least-squares modification of the Stokes formula. The new gravimetric geoid model, IRG04, agrees considerably better with GPS/levelling than any of the other recent local geoid model in the area. Its RMS fit with GPS/levelling is 0.27 m and 3.8 ppm in the absolute and relative view, respectively. The relative accuracy of IRG04 is four times better than the most recently published global and regional geoid models available in this area. This progress shows the practical potential of the method of least-squares modification of Stokes's formula in combination with heterogeneous data for regional geoid determination.

  • 7.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
    Hybrid precise gravimetric geoid model for Iran based on recent GRACE and SRTM data and the least squares modification of Stokes formula2006In: J. Physics of Earth and Space, Vol. 32, no 1, p. 7-23Article in journal (Refereed)
    Abstract [en]

    Since 1986, several gravimetric geoid models have been published in the Iran region. It was found thatthe standard deviation of fitting between these models versus GPS/levelling data in most cases was worsethan the currently available global geopotential models. A new hybrid gravimetric geoid model computed(IRG04) by using the least squares modification of Stokes formula based on the recent published GRACEbased global geopotential model, the high-resolution Shuttle SRTM global digital terrain model and anew Iranian gravity anomaly database. The absolute and relative accuracies of the new geoid model testedversus the GPS/levelling points and they are estimated about 0.27 m and 3.8 ppm, respectively.Additional comparison between the IRG04 and the recent published gravimetric geoid models shows thatthe relative accuracy of the IRG04 is almost 4 times better than the most recent published models in thisarea.

  • 8.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
    Precise Gravimetric Geoid Model for Iran Based on GRACE and SRTM Data and the Least-Squares Modification of Stokes’ Formula: with Some Geodynamic Interpretations2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Iran is one of the most complicated areas in the world from the view of rough topography, tectonic activity, large lateral density and geoidal height variations. The computation of a regional gravimetric geoid model with high accuracy in mountainous regions, especially with sparse data, is a difficult task that needs a special attention to obtain reliable results which can meet the needs of the today geodetic community.

    In this research different heterogeneous data has been used, which includes gravity anomalies, the high-resolution SRTM Digital Elevation Model (DEM), recently published GRACE Global Geopotential Models (GGMs), geological maps and GPS/levelling data. The above data has been optimally combined through the least-squares modification of Stokes formula with additive corrections. Regarding the data evaluation and refinement, the cross-validation technique has been used for detection of outliers. Also, several GGMs and DEMs are evaluated with GPS/levelling data. The impact of utilizing a high resolution SRTM DEM to improve the accuracy of the geoid model has been studied. Also, a density variation model has been established, and its effect on the accuracy of the geoid was investigated. Thereafter a new height datum for Iran was established based on the corrective surface idea. Finally, it was found that there is a significant correlation between the lateral geoid slope and the tectonic activities in Iran.

    We show that our hybrid gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models in the area. Its RMS fit with GPS/levelling is 27 cm and 3.8 ppm in the absolute and relative senses, respectively. Moreover, the relative accuracy of the IRG04 geoid model is at least 4 times better than any of the previously published global and regional geoid models in the area. Also, the RMS fit of the combined surface model (IRG04C) versus independent precise GPS/levelling is almost 4 times better compared to the original gravimetric geoid model (IRG04). These achievements clearly show the effect of the new gravity database and the SRTM data for the regional geoid determination in Iran based on the least-squares modification of Stokes’ formula.

  • 9.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    Qualification and refinement of the gravity database based on cross-validation approach, A case study of Iran2007In: Acta Geodaetica et Geophysica, ISSN 1217-8977, Vol. 42, no 3, p. 285-295Article in journal (Refereed)
    Abstract [en]

    In this article, we propose a technique for the precise cleaning of the gravity anomaly database based on the cross validation approach. The terrestrial gravity anomalies were compared versus a global geopotential model and take into account the effect of topography in this comparison. The efficiency of the cross-validation technique is illustrated in outlier detection as well as in choosing the proper gridding technique as a case study in construction of the Iranian new gravity database. In order to reduce the effect of topography and the discretisation error, a special interpolation scheme is used for gridding of the free-air gravity anomalies. The final grid file was created based on the Kriging method with 80" x 90" block resolution. The overall accuracy for the new Iranian gravity database is estimated in the order of 10 mGal.

  • 10.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Qualification and refinement of the Iranian gravity database2005Conference paper (Other academic)
  • 11.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    The Impact of lateral density variation model in the determination of precise gravimetric geoid in mountainous areas: A case study of Iran2006In: Geophysical Journal International., ISSN 0956-540X, Vol. 167, no 2, p. 521-527Article in journal (Refereed)
    Abstract [en]

    The existence of topography above the geoid violates the basic assumption of Stokes' formula for the determination of the geoid. Usually a constant density of 2.67 g cm(-3) is used in the determination of the geoid. However, we know that the density of the topographical mass departs by about 10-20 per cent from the actual mean value of the crustal density. Iran has one of the largest relief and density variations in the world and the geoid computation in this area is affected the most by topographical density effects. The influence on the geoid height coming from the actual and Pratt-Hayford's isostatic models are studied. Numerical results show that the differences in the geoid height due to actual and isostatic density models can reach up to 0.22 and 0.29 m, respectively, which is not negligible in a precise geoid determination with centimetre accuracy. Our results suggest that the effect of topographical density lateral variations is significant enough and ought to be taken into account specially in mountainous regions in the determination of a precise geoid model.

  • 12.
    Kiamehr, Ramin
    et al.
    Department of Geodesy and Geomatics, Zanjan University, Iran).
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Geoinformatics.
    Estimating variance components of ellipsoidal, orthometric and geoidalheights through the GPS/levelling Network in Iran2008In: Journal of the Earth and Space Physics, ISSN 0378-1046, Vol. 34, no 3, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The Best Quadratic Unbiased Estimation (BQUE) of variance components in the Gauss-Helmert model is used to combine adjustment of GPS/levelling and geoid to determinethe individual variance components for each of the three height types. Through theresearch, different reasons for achievement of the negative variance components werediscussed and a new modified version of the Best Quadratic Unbiased Non-negativeEstimator (MBQUNE) was successfully developed and applied. This estimation could beuseful for estimating the absolute accuracy level which can be achieved using theGPS/levelling method. A general MATLAB function is presented for numericalestimation of variance components by using the different parametric models. Themodified BQUNE and developed software was successfully applied for estimating thevariance components through the sample GPS/levelling network in Iran. In the followingresearch, we used the 75 outlier free and well distributed GPS/levelling data. Threecorrective surface models based on the 4, 5 and 7 parameter models were used throughthe combined adjustment of the GPS/levelling and geoidal heights. Using the 7-parametermodel, the standard deviation indexes of the geoidal, geodetic and orthometric heights inIran were estimated to be about 27, 39 and 35 cm, respectively.

  • 13. Kiamehr, Ramin
    et al.
    Eshagh, Mehdi
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Interpretation of general geophysical patterns in Iran based on GRACE gradient component analysis2008In: Acta Geophysica, ISSN 1895-6572, Vol. 56, no 2, p. 440-454Article in journal (Refereed)
    Abstract [en]

    Only with satellites it is possible to cover the entire Earth densely with gravity field related measurements of uniform quality within a short period of time. However, due to the altitude of the satellite orbits, the signals of individual local masses are strongly damped. Based on the approach of Petrovskaya and Vershkov we determine the gravity gradient tensor directly from the spherical harmonic coefficients of the recent EIGEN-GL04C combined model of the GRACE satellite mission. Satellite gradiometry can be used as a complementary tool to gravity and geoid information in interpreting the general geophysical and geodynamical features of the Earth. Due to the high altitude of the satellite, the effects of the topography and the internal masses of the Earth are strongly damped. However, the gradiometer data, which are nothing else than the second order spatial derivatives of the gravity potential, efficiently counteract signal attenuation at the low and medium frequencies.

    In this article we review the procedure for estimating the gravity gradient components directly from spherical harmonics coefficients. Then we apply this method as a case study for the interpretation of possible geophysical or geodynamical patterns in Iran. We found strong correlations between the cross-components of the gravity gradient tensor and the components of the deflection of vertical, and we show that this result agrees with theory. Also, strong correlations of the gravity anomaly, geoid model and a digital elevation model were found with the diagonal elements of the gradient tensor.

  • 14.
    Kiamehr, Ramin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301).
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Analysis of Surface Deformation Patterns Analysis Using 3D Finite Elements Method: A case study in Skåne area, Sweden2005In: J. Geodynamics, ISSN 0264-3707, Vol. 39, no 4, p. 403-412Article in journal (Refereed)
    Abstract [en]

    The application of geodetic techniques to study crustal deformations associated with the geodynamic activity of a region is considered as a fundamental tool in seismic risk mitigation and in earthquake prediction research. In principle, the crustal deformation analysis is a purely geodetic problem as it concerns alteration of the Earth shape, so that deformations of the crust are directly connected with geodetic observables. The Tornquist zone across Skane in southern Sweden is a classical fault zone that separates the Precambrium gneisses of the Baltic shield in the north from Phanerozoic Europe to the south. In this region, a Global Positioning Network (GPS) was established to study possible crustal motions. The aim of this article is to improve on previous study in to estimate the possible crustal strains and dilation parameters by a finite element analysis. Results show that the areas with maximum shear strain and dilation are located exactly in the active fault zones and their intersections. However, further observations in a dense network as well as integration with geological and geophysical data are needed to fully explore the recent crustal motions over the Tornquist zone.

  • 15.
    Kiamehr, Ramin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Comparison of the qualities of recent global and local gravimetric geoid models in Iran2005In: Studia Geophysica et Geodaetica, ISSN 0039-3169, Vol. 49, no 3, p. 289–304-Article in journal (Refereed)
    Abstract [en]

    A number of regional gravimetric geoid models have recently been determined for the Iran area, and a common problem is to select the best model, e.g. for engineering applications. A related problem is that in order to improve the local geoid models, the selection of the best Global Geopotential Model (GGM) model for the region is essential, to be used in a combined solution from GGM and local gravimetric data. We discuss these problems by taking advantage of 260 GPS/levelling points as an external tool for validation of different global and local geoid models in the absolute and relative senses. By using relative comparisons of the height differences between precise levelling and GPS/geoid models we avoid possible unknown systematic effects between the different types of observables.

    The study shows that the combination of the newly released GRACE model (GGM02C) with EGM96 geoid model fits the GPS/levelling data in Iran with the best absolute and relative accuracy among the GGMs. Among the local geoid models, the newly gravimetric geoid model IRG04 agrees considerably better with GPS/levelling than any of the other recent local geoid models. Its rms fit with GPS/levelling is 55 cm. Hence, we strongly recommend the use of this new model in any surveying engineering or GPS/levelling projects in the area.

  • 16.
    Kiamehr, Ramin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Effect of the SRTM global DEM on the determination of a high-resolution geoid model: a case study in Iran2005In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, J. Geodesy, Vol. 79, no 9, p. 540-551Article in journal (Refereed)
    Abstract [en]

    Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographic and downward continuation (DWC) corrections in the application of Stokes's formula. The effects of these errors are assessed by the evaluation of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say 16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development. We also found very large differences between the GLOBE and SRTM models on the range of -750 to 550 m. This difference causes an error in the range of -160 to 140 mGal in interpolating surface gravity anomalies and -60 to 60 mGal in simple Bouguer anomaly correction terms. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs, in the range of -1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points only differs by 3 cm for these two DEMs.

  • 17.
    Kiamehr, Ramin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics.
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics, Geodesy.
    Impact of the precise geoid model in studying tectonic structures- a case study in Iran2006In: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, J. Geodynamics, Vol. 42, no 1-3, p. 1-11Article in journal (Refereed)
    Abstract [en]

    Iran is one of the most active regions in the world with respect,to earthquakes and tectonic motions in the lithosphere. In order to study the impact of the geoid model in detecting plate tectonic boundaries and in the establishment of an accurate height datum for future geodynamic observations, a new combined gravimetric geoid model for Iran (IRG04C) was computed by the method of least squares modification of Stokes formula based on the most recent gravity anomaly database, SRTM high resolution Digital Elevation Model (DEM), GRACE GGM02 Global Geopotential Model and GPS/levelling data. The RMS fit of the new geoid model versus GPS/levelling data is 9 cm, which is a 10 times better fit compared to the most recent published gravimetric geoid model in the area. An integrated approach, combining gravity, geoid and seismology data as well as a digital elevation model, was used to find possible correlations between these parameters. Our investigation indicates that all earthquakes with magnitude over 6.0 in the Richter scale are located in areas with a geoid slope exceeding 7.5%. The study shows a significant correlation between the horizontal gradient of the geoid and plate tectonic activities.

  • 18.
    Sjöberg, Lars E.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Kiamehr, Ramin
    Zanjan University, Iran.
    Ågren, Jonas
    Least Squares Modification of Stokes Formula vs. Remove-Compute-Restore Technique2009In: Geophysical Research Abstracts: Vol. 11, EGU2009-4068-2, 2009, 2009Conference paper (Refereed)
    Abstract [en]

    Today's applications of Stokes' formula combine the classical formula with an Earth Gravity model (EGM). In the remove-compute-restore technique this is performed by removing the EGM from the gravity anomaly together with the direct gravity effects for topography, atmosphere, etc. After the Stokes integration all these effects are restored on the geoid height. In the least squares modification of Stokes' formula the integration is carried out without such direct effects, but all corrections are added as combined effects (direct plus indirect effects) to the computed preliminary geoid heights. The two strategies for geoid determination are compared both theoretically and in a numerical example vs. GPS-levelling over Sweden.

  • 19. Ågren, J.
    et al.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Sjöberg, Lars
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Computation of a New Gravimetric Geoid Model over Sweden using the KTH Method: Paper presented at FIG working week, 14-18 June 2008, Stockholm, Sweden2008In: FIG working week, 2008Conference paper (Refereed)
  • 20.
    Ågren, Jonas
    et al.
    National Land Survey of Sweden.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Numerical comparison of two strategies for geoid and quasi geoid determination over Sweden2007Conference paper (Refereed)
  • 21.
    Ågren, Jonas
    et al.
    Lantmäteriet (National Land Survey).
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Progress in the determination of a gravimetric quasigeoid model over Sweden2006Conference paper (Refereed)
    Abstract [en]

    One alternative to the traditional remove-compute-restore procedure that has hitherto been used to compute the Nordic geoid is to use the least squares modification method with additive corrections. This technique, which has been developed at the Royal Institute of Technology (KTH) in Stockholm, includes the least squares kernel modification together with topographic, downward continuation, atmospheric and ellipsoidal corrections.This paper presents the most recent results from an on-going joint project between KTH and Lantmäteriet (National Land Survey of Sweden), whose main purpose is to evaluate the KTH approach numerically and to compute a gravimetric quasigeoid model for Sweden. The work should also be viewed as being conducted under the umbrella of the working group for geoid determination of the Nordic Geodetic Commission (NKG). The evaluation is made using 108 high quality GPS/levelling height anomalies covering the major parts of Sweden except for the mountainous areas to the North West. After a 4-parameter fit, the most promising attempt achieves a RMS value for the residuals of 17 mm, which should be compared to the 28 mm RMS reached by the NKG 2004 model. It is concluded that the least squares modification method with additive corrections is a promising alternative for the future.

  • 22. Ågren, Jonas
    et al.
    Kiamehr, Ramin
    Zanjan University.
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    The new gravimetric quasigeoid model KTH08 over Sweden2009In: Journal of Applied Geodesy, ISSN 1862-9024, Vol. 3, no 3, p. 143-153Article in journal (Refereed)
    Abstract [en]

    The least squares modification of Stokes formula has been developed in a series of papers published in Journal of Geodesy between 1984 and 2008. It consists of a least squares (stochastic) Stokes kernel modification with additive corrections for the topography, downward continuation, the atmosphere and the ellipsoidal shape of the Earth. The method, developed at the Royal Institute of Technology (KTH) will here be denoted by the abbreviated name the KTH method.

    This paper presents the computational results of a new gravimetric quasigeoid model over Sweden (the KTH08 model) by employing the KTH method. Traditionally the Nordic Geodetic Commission (NKG) has computed gravimetric quasigeoid models over Sweden and other Nordic countries; the latest model being NKG 2004. Another aim of this paper is therefore to compare KTH08 and NKG 2004 quasigeoid models and to evaluate their accuracies using GNSS/levelling height anomalies. The rms fit of KTH08 in 196 GNSS data points distributed over Sweden by using a 1(4)-parameter transformation is 22 (20) mm. It is concluded that KTH08 is a significant step forward compared to NKG 2004.

  • 23.
    Ågren, Jonas
    et al.
    National Land Survey of Sweden.
    Kiamehr, Ramin
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    Sjöberg, Lars Erik
    KTH, School of Architecture and the Built Environment (ABE), Transport and Economics (closed 20110301), Geodesy (closed 20110301).
    The Swedish geoid as evaluated by the method of least-squares modification with additive corrections2006Conference paper (Refereed)
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