| 1. |
- Abrehdary, Majid, 1983-, et al.
(författare)
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A New Moho Depth Model for Fennoscandia with Special Correction for the Glacial Isostatic Effect
- 2021
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Ingår i: Pure and Applied Geophysics. - : Springer Nature. - 0033-4553 .- 1420-9136. ; 178:3, s. 877-888
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a new Moho depth model in Fennoscandia and its surroundings. The model is tailored from data sets of XGM2019e gravitationl field, Earth2014 topography and seismic crustal model CRUST1.0 using the Vening Meinesz-Moritz model based on isostatic theory to a resolution of 1° × 1°. To that end, the refined Bouguer gravity disturbance is determined by reducing the observed field for gravity effect of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components. Moreover, stripping of non-isostatic effects of gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA), i.e., the effect of future GIA, and plate flexure has also been performed. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and gravimetric Moho depth determination in this area. One may ask whether the DGIA effect is sufficiently well removed in the application of the general non-isostatic effects in such an area, and to answer this question, the Moho depth is determined both with and without specific removal of the DGIA effect prior to non-isostatic effect and Moho depth determinations. The numerical results yield that the RMS difference of the Moho depth from our model HVMD19 vs. the seismic CRUST19 and GRAD09 models are 3.8/4.2 km and 3.7/4.0 km when the above strategy for removing the DGIA effect is/is not applied, respectively, and the mean value differences are 1.2/1.4 km and 0.98/1.4 km, respectively. Hence, our study shows that the specific correction for the DGIA effect on gravity disturbance is slightly significant, resulting in individual changes in the gravimetric Moho depth up to − 1.3 km towards the seismic results. On the other hand, our study shows large discrepancies between gravimetric and seismic Moho models along the Norwegian coastline, which might be due to uncompensated non-isostatic effects caused by tectonic motions.
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| 2. |
- Abrehdary, Majid, 1983-, et al.
(författare)
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Moho density contrast in Antarctica determined by satellite gravity and seismic models
- 2021
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 225:3, s. 1952-1962
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Tidskriftsartikel (refereegranskat)abstract
- As recovering the crust-mantle/Moho density contrast (MDC) significantly depends on the properties of the Earth's crust and upper mantle, varying from place to place, it is an oversimplification to define a constant standard value for it. It is especially challenging in Antarctica, where almost all the bedrock is covered with a thick layer of ice, and seismic data cannot provide a sufficient spatial resolution for geological and geophysical applications. As an alternative, we determine the MDC in Antarctica and its surrounding seas with a resolution of 1 degrees x 1 degrees by the Vening Meinesz-Moritz gravimetric-isostatic technique using the XGM2019e Earth Gravitational Model and Earth2014 topographic/bathymetric information along with CRUST1.0 and CRUST19 seismic crustal models. The numerical results show that our model, named HVMDC20, varies from 81 kg m(-3) in the Pacific Antarctic mid-oceanic ridge to 579 kg m(-3) in the Gamburtsev Mountain Range in the central continent with a general average of 403 kg m(-3). To assess our computations, we compare our estimates with those of some other gravimetric as well as seismic models (KTH11, GEMMA12C, KTH15C and CRUST1.0), illustrating that our estimates agree fairly well with KTH15C and CRUST1.0 but rather poor with the other models. In addition, we compare the geological signatures with HVMDC20, showing how the main geological structures contribute to the MDC. Finally, we study the remaining glacial isostatic adjustment effect on gravity to figure out how much it affects the MDC recovery, yielding a correlation of the optimum spectral window (7 <= n <= 12) between XGM2019e and W12a GIA models of the order of similar to 0.6 contributing within a negligible +/- 14 kg m(-3) to the MDC.
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| 3. |
- Abrehdary, Majid, 1983-, et al.
(författare)
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Recovering Moho constituents from satellite altimetry and gravimetric data for Europe and surroundings
- 2019
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Ingår i: Journal of Applied Geodesy. - : WALTER DE GRUYTER GMBH. - 1862-9016 .- 1862-9024. ; 13:4, s. 291-303
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Tidskriftsartikel (refereegranskat)abstract
- In this research, we present a local Moho model, named MOHV19, including Moho depth and Moho density contrast (or shortly Moho constituents) with corresponding uncertainties, which are mapped from altimetric and gravimetric data (DSNSC08) in addition to seismic tomographic (CRUST1.0) and Earth topographic data (Earth2014) to a resolution of 1 degrees x 1 degrees based on a solution of Vening Meinesz-Moritz' theory of isostasy. The MOHV19 model covers the area of entire European plate along with the surrounding oceans, bounded by latitudes (30 degrees N-82 degrees N) and longitudes (40 degrees W-70 degrees E). The article aims to interpret the Moho model resulted via altimetric and gravimetric information from the geological and geophysical perspectives along with investigating the relation between the Moho depth and Moho density contrast. Our numerical results show that estimated Moho depths range from 7.5 to 57.9 km with continental and oceanic averages of 41.3 +/- 4.9 km and 21.6 +/- 9.2 km, respectively, and an overall average of 30.9 +/- 12.3 km. The estimated Moho density contrast ranges from 60.2 to 565.8 kg/m(3), with averages of 421.8 +/- 57.9 and 284.4 +/- 62.9 kg/m(3) for continental and oceanic regions, respectively, with a total average of 350.3 +/- 91.5 kg/m(3). In most areas, estimated uncertainties in the Moho constituents are less than 3 km and 40 kg/m(3), respectively, but they reach to much more significant values under Iceland, parts of Gulf of Bothnia and along the Kvitoya Island. Comparing the Moho depths estimated by MOHV19 and those derived by CRUST1.0, MDN07, GRAD09 and MD19 models shows that MOHV19 agree fairly well with CRUST1.0 but rather poor with other models. The RMS difference between the Moho density contrasts estimated by MOHV19 and CRUST1.0 models is 49.45 kg/m(3).
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| 4. |
- Abrehdary, Majid, et al.
(författare)
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Remaining non-isostatic effects in isostatic-gravimetric Moho determination-is it needed?
- 2023
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 234:3, s. 2066-2074
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Tidskriftsartikel (refereegranskat)abstract
- For long time the study of the Moho discontinuity (or Moho) has been a crucial topic in inferring the dynamics of the Earth's interior, and with profitable result it is mapped by seismic data, but due to the heterogeneous distribution of such data the quality varies over the world. Nevertheless, with the advent of satellite gravity missions, it is today possible to recover the Moho constituents (i.e. Moho depth; MD and Moho density contrast; MDC) via gravity observations based on isostatic models. Prior to using gravity observations for this application it must be stripped due to the gravitational contributions of known anomalous crustal density structures, mainly density variations of oceans, glacial ice sheets and sediment basins (i.e. stripping gravity corrections). In addition, the gravity signals related mainly with masses below the crust must also be removed. The main purpose of this study is to estimate the significance of removing also remaining non-isostatic effects (RNIEs) on gravity, that is, gravity effects that remain after the stripping corrections. This is carried out by using CRUST19 seismic crustal model and employing Vening Meinesz-Moritz (VMM) gravimetric-isostatic model in recovering the Moho constituents on a global scale to a resolution of 1 degrees x 1 degrees. To reach this goal, we present a new model, named MHUU22, formed by the SGGUGM2 gravitational field, Earth2014 topography, CRUST1.0 and CRUST19 seismic crustal models. Particularly, this study has its main emphasis on the RNIEs on gravity and Moho constituents to find out if we can modify the stripping gravity corrections by a specific correction of the RNIEs. The numerical results illustrate that the RMS differences between MHUU22 MD and the seismic model CRUST1.0 and least-squares combined model MOHV21 are reduced by 33 and 41 per cent by applying the NIEs, and the RMS differences between MHUU22 MDC and the seismic model CRUST1.0 and least-squares combined model MDC21 are reduced by 41 and 23 per cent when the above strategy for removing the RNIEs is applied. Hence, our study demonstrates that the specific correction for the RNIEs on gravity disturbance is significant, resulting in remarkable improvements in MHUU22, which more clearly visualize several crustal structures.
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| 5. |
- Abrehdary, Majid, et al.
(författare)
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Towards the Moho depth and Moho density contrast along with their uncertainties from seismic and satellite gravity observations
- 2017
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 11:4, s. 231-247
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined method for estimating a new global Moho model named KTH15C, containing Moho depth and Moho density contrast (or shortly Moho parameters), from a combination of global models of gravity (GOCO05S), topography (DTM2006) and seismic information (CRUST1.0 and MDN07) to a resolution of 1° × 1° based on a solution of Vening Meinesz-Moritz’ inverse problem of isostasy. This paper also aims modelling of the observation standard errors propagated from the Vening Meinesz-Moritz and CRUST1.0 models in estimating the uncertainty of the final Moho model. The numerical results yield Moho depths ranging from 6.5 to 70.3 km, and the estimated Moho density contrasts ranging from 21 to 650 kg/m3, respectively. Moreover, test computations display that in most areas estimated uncertainties in the parameters are less than 3 km and 50 kg/m3, respectively, but they reach to more significant values under Gulf of Mexico, Chile, Eastern Mediterranean, Timor sea and parts of polar regions. Comparing the Moho depths estimated by KTH15C and those derived by KTH11C, GEMMA2012C, CRUST1.0, KTH14C, CRUST14 and GEMMA1.0 models shows that KTH15C agree fairly well with CRUST1.0 but rather poor with other models. The Moho density contrasts estimated by KTH15C and those of the KTH11C, KTH14C and VMM model agree to 112, 31 and 61 kg/m3 in RMS. The regional numerical studies show that the RMS differences between KTH15C and Moho depths from seismic information yields fits of 2 to 4 km in South and North America, Africa, Europe, Asia, Australia and Antarctica, respectively.
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| 6. |
- Albertsson-Wikland, Kerstin, 1947, et al.
(författare)
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Swedish references for weight, weight-for-height and body mass index: The GrowUp 1990 Gothenburg study
- 2021
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Ingår i: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 110, s. 537-548
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Tidskriftsartikel (refereegranskat)abstract
- Aim To update the Swedish references for weight, weight-for-height and body mass index (BMI) considering the secular trend for height but not including that for weight. Methods Longitudinal measures of height and weight were obtained (0-18 years) from 1418 (698 girls) healthy children from the GrowUp 1990 Gothenburg cohort born at term to non-smoking mothers and Nordic parents. A total of 145 individuals with extreme BMI value vs GrowUp 1974 BMI SDS reference were excluded (0-2 years: +/- 4SDS, 2 < years: -3SDS, +2.3SDS). References were constructed using the LMS method. Results The updated weight reference became similar to the GrowUp 1974 Gothenburg reference: BMI increased rapidly up to lower levels in the 1990 cohort during infancy/early childhood, similar in both groups in late childhood/adolescence, despite lower values at +2SDS. Compared with the WHO weight standard, median and -2SDS weight values were higher for the 1990 cohort, whereas +2SDS values were lower, resulting in narrower normal range. Median values were greater and +/- 2SDS narrower for the 1990 vs the WHO weight-for-height reference. International Obesity Task force (IOTF) BMI lines for definitions for over- and underweight were added. Conclusion We present updated references for weight, weight-for-height and BMI, providing a healthy goal for weight development when monitoring growth within healthcare settings.
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| 7. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Optimization of GNSS Deformation Monitoring Networks by Considering Baseline Correlations
- 2016
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Ingår i: FIG Working Week 2016 Proceedings.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the study of deformations of man-made constructions or in geodynamics one usually needs to carefully monitor fixed objects attached to the deformable body. The purpose is to use precise observations to build up an accurate, reliable and possibly low-cost network around the objects to study their motion in short- or long-time intervals and to estimate the possible displacements or deformations among those objects. Frequently, such studies are performed to prevent unwanted disasters (e.g. due to earthquakes and landslides as well as the progressive or abrupt destruction of large-scale structures). This study is concerned with designing an optimal GNSS network to monitor possible deformations of a geodetic network.By considering GNSS observations one can perform the optimization according to some pre-defined criteria and come up with the best location of receivers and optimum number of baselines. In practice, it is quite common to neglect the effect of correlations between baselines, and instead use single-baseline adjusted data in the optimisation procedure. However, in each session of observation usually more than two receivers are simultaneously taking data from a number of common GNSS satellites. This procedure inevitably leads to between-baseline correlations. Our study designs an optimal observation plan for a GNSS monitoring network with the aim of determining possible displacements and deformations. The developed methodology will be tested on a simulated network with five points, where three receivers simultaneously take data from four satellites.
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| 8. |
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| 9. |
- Amin, Hadi
(författare)
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Study on the Earth’s Surface Mass Variations using Satellite Gravimetry Observations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our complex planet is continuously undergoing temporal and spatial changes. In this context, ongoing processes in the Earth subsystems (geosphere, biosphere, cryosphere, hydrosphere, and atmosphere) cause changes in the gravity field of the Earth across a wide range of temporal and spatial scales. Accordingly, by both spatially and temporally tracing our planet’s ever-changing gravity field, scientists can better constrain the underlying processes contributing to such dynamic changes of mass distribution within the Earth system. Monitoring the Earth’s gravity field and its temporal variations is essential, among others, for tracking disasters and specifying land areas with a high risk of flooding, earthquakes, and droughts, movements of tectonic plates, and providing accurate positioning through satellite positioning technology. On short-term timescales, temporal variations in the Earth’s gravity field are mainly caused by the movement of water in its various forms. Accordingly, sea-level variations and ice-sheet and glacier changes, which are known as critical indicators of global warming and climate change, can be accurately monitored by tracking the Earth’s gravity field changes. Since there is a close link between water redistribution and the Earth’s energy cycle, climate system, food security, human and ecosystem health, energy generation, economic and societal development, and climate extremes (droughts and floods), it is essential to accurately monitor water mass exchange between the Earth system components. Among all observational techniques, satellite gravimetry has provided an integrated global view of ongoing processes within the Earth system. The current generation of satellite gravimetry missions (the Gravity Recovery and Climate Experiment (GRACE) mission and its successor, GRACE Follow-On) has dramatically revolutionized our understanding of dynamic processes in the Earth’s surface and, consequently, has significantly improved our understanding of the Earth’s climate system. By considering different aspects of studying the Earth’s gravity field, this thesis brings new insights to the determination and analysis of the mass change in the Earth system. First, by studying the shortcomings of the common techniques of estimating the geoid potential, a new approach is examined that simultaneously estimates the geoid potential, W0, and the geometrical parameters of the reference Mean Earth Ellipsoid (MEE). In this regard, as the geoid needs to be considered as a static equipotential surface, the sensitivity of the estimations to the time dependent Earth’s gravity field changes is studied. Secondly, relying on the GRACE monthly gravity fields and the complementary observational techniques, and by pushing the limit of GRACE, mass redistribution over land and ocean is investigated. Within the ocean, satellite altimetry and Argo products are utilized along with the GRACE monthly solutions for quantifying the global barystatic sea-level change and assessing the closure of the global mean sea level budget. Over land, a region with relatively high temporal mass change (oil and water extraction) is chosen in which by taking advantage of having in-situ observations and hydrological models, the ability of GRACE products in quantifying the changes in groundwater storage is studied. In this frame, for both the ocean and land studies, different aspects of the processing of GRACE monthly gravity fields are investigated and GRACE inherent errors are addressed appropriately to arrive at reliable and accurate estimates of the Earth’s surface mass change. As the final contribution in this thesis, a rigorous analytical model for detecting surface mass change from the time-variable gravity solutions is proposed and examined in different case studies of surface mass change. Since the launch of the GRACE twin satellites, the GRACE(-FO) time-varying gravity fields are conventionally converted into the surface mass change using a spherical analytical model that approximates the Earth by a sphere. More recently, the analytical mass change detection model has been improved by considering an ellipsoid as the shape of the Earth, which improved the previous estimations of surface mass change, especially over high latitudes with relatively large mass change signals. However, by taking into account the real shape of the Earth and considering more realistic assumptions, a new analytical solution for the problem of surface mass change detection from the time-varying gravity fields is proposed in this thesis. It is shown that the simplistic spherical and ellipsoidal geometries are no longer tenable and the new model surpasses the common spherical approach and its ellipsoidal version.
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| 10. |
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| 11. |
- Goyal, Ropesh, et al.
(författare)
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Empirical comparison between stochastic and deterministic modifiers over the French Auvergne geoid computation test-bed
- 2022
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Ingår i: Survey review - Directorate of Overseas Surveys. - : Taylor & Francis. - 0039-6265 .- 1752-2706. ; 54:382, s. 57-69
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Tidskriftsartikel (refereegranskat)abstract
- Since 2006, several different groups have computed geoid and/or quasigeoid (quasi/geoid) models for the Auvergne test area in central France using various approaches. In this contribution, we compute and compare quasigeoid models for Auvergne using Curtin University of Technology’s and the Swedish Royal Institute of Technology’s approaches. These approaches differ in many ways, such as their treatment of the input data, choice of type of spherical harmonic model (combined or satellite-only), form and sequence of correction terms applied, and different modified Stokes’s kernels (deterministic or stochastic). We have also compared our results with most of the previously reported studies over Auvergne in order to seek any improvements with respect to time [exceptions are when different subsets of data have been used]. All studies considered here compare the computed quasigeoid models with the same 75 GPS-levelling heights over Auvergne. The standard deviation for almost all of the computations (without any fitting) is of the order of 30–40 mm, so there is not yet any clear indication whether any approach is necessarily better than any other nor improving over time. We also recommend more standardisation on the presentation of quasi/geoid comparisons with GPS-levelling data so that results from different approaches over the same areas can be compared more objectively.
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| 12. |
- Hardling, Mats, et al.
(författare)
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Serial monitoring of BCR-ABL transcripts in chronic myelogenous leukemia (CML) treated with imatinib mesylate
- 2004
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Ingår i: Med Oncol. - 1357-0560. ; 21:4, s. 349-58
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Tidskriftsartikel (refereegranskat)abstract
- Survival among chronic myelogenous leukemia (CML) patients can be linked to the reduction in leukemic cell burden. Treatment with imatinib mesylate results in a high frequency of complete cytogenetic response, which can be further stratified using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). We have serially monitored peripheral blood and bone marrow BCR-ABL transcripts using qRT-PCR in CML patients commencing imatinib therapy, and compared the results with bone marrow cytogenetics. Seventeen patients (aged 25-74 yr) with Philadelphia chromosome positive CML in first chronic phase were treated with imatinib targeting a dose of 400 mg/d. The median follow up is 30 mo (range 9-33 mo). Every third month the product of the BCR-ABL fusion gene was evaluated in both blood and bone marrow specimens by real-time RT-PCR using the TaqMan probe system. In 113 simultaneously obtained blood and bone marrow samples, the BCR-ABL transcript values agreed well with cytogenetic data. Blood and bone marrow specimens gave comparable values for BCR-ABL transcripts. Before start of imatinib therapy there was a considerable variation in BCR-ABL transcripts among the patients, ranging approximately one log (base 10). Similarly, patients with a complete cytogenetic response following imatinib therapy had variable BCR-ABL transcript levels, ranging at least three logs (base 10). The major decline in BCR-ABL transcripts occurred within 6 mo after start of imatinib therapy. The decline in BCR-ABL transcripts, following imatinib therapy, appears to level off at 12-15 mo. Two late responders were identified with a still decreasing level in BCR-ABL transcripts after 24 mo of treatment. It is concluded that BCR-ABL mRNA quantification in peripheral blood is suitable for routine monitoring of the response to treatment and long-term disease status in CML, especially in patients who have achieved a complete cytogenetic response. A plateau in BCR-ABL transcripts seems to have been reached after 12-15 mo of imatinib treatment; however, some "late responders" are seen.
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| 13. |
- Holmgren, Anton, et al.
(författare)
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Detailed analyzes of the relation between childhood BMIand gain in height during puberty, separated into different Components
- 2016
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Ingår i: International Journal of Obesity. - 0307-0565 .- 1476-5497.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background: We have previously found that childhood BMI is inversely related to pubertal height gain: overweight/obese children of both genders have less specific pubertal height gain. The QEPS-model (describing total growth in height as a combination of four mathematical functions), can be used for calculation of estimates of pubertal growth. Growth in height during puberty can be described as a combination of continuous ongoing growth, Q(ES), and a specific pubertal growth function, P. Objectives: To investigate the importance of when overweight/obesity starts during childhood in relation to subsequent growth in height during puberty; and to study the relationship between childhood BMI and pubertal growth functions from the QEPS-model in greater detail than previously presented. Material/Methods: The longitudinally followed GrowUpGothenburg 1990 birth cohort, with growth data from birth until adult height was analyzed, using the QEPS-model. Individual BMI-SDS values, from 3.5–8.0 years of age (n = 1901) were calculated for linear and subgroup analyses (normal /underweight, NwUw, overweight/obese, OwOb), based on the IOTF 2012 reference2. Relationships between childhood-BMI and total pubertal height gain were considered according to P-function and Q(ES)-function. Results: We found no significant difference in pubertal height gain depending on when in childhood the BMI-SDS peaked, in either sex. In general, the total pubertal growth in girls depended more on the continuous Q(ES)-function than P-function and this balance was shifted towards less P-function with higher BMI-SDS, especially for Ob girls (figure, left). NwUw boys had pubertal gain mostly from the P-function, for the Ow boys the pattern was more mixed and for Ob boys all had less P- than Q(ES)-function (figure, right). Conclusion: The results of the present study have shown that the reduced pubertal gain in height for OwOb children is not related to when during childhood the BMI peaked. For both genders, the pubertal gain shifted to less specific pubertal growth (P) and relatively more continuous growth (Q(ES)) with higher BMI-SDS.
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| 14. |
- Holmgren, Anton, et al.
(författare)
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Estimating secular changes in longitudinal growth patterns underlying adult height with the QEPS model: the Grow Up Gothenburg cohorts
- 2018
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Ingår i: Pediatric Research. - : Springer Science and Business Media LLC. - 0031-3998 .- 1530-0447. ; 84:1, s. 41-49
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Over the past 150 years, humans have become taller, and puberty has begun earlier. It is unclear if these changes are continuing in Sweden, and how longitudinal growth patterns are involved. We aimed to evaluate the underlying changes in growth patterns from birth to adulthood by QEPS estimates in two Swedish cohorts born in 1974 and 1990. METHODS: Growth characteristics of the longitudinal 1974 and 1990-birth cohorts (n = 4181) were compared using the QEPS model together with adult heights. RESULTS: There was more rapid fetal/infancy growth in girls/boys born in 1990 compared to 1974, as shown by a faster Etimescale and they were heavier at birth. The laterborn were taller also in childhood as shown by a higher Q-function. Girls born in 1990 had earlier and more pronounced growth during puberty than girls born in 1974. Individuals in the 1990 cohort attained greater adult heights than those in the 1974 cohort; 6 mm taller for females and 10 mm for males. CONCLUSION: A positive change in adult height was attributed to more growth during childhood in both sexes and during puberty for girls. The QEPS model proved to be effective detecting small changes of growth patterns, between two longitudinal growth cohorts born only 16 years apart.
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| 15. |
- Holmgren, Anton, et al.
(författare)
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Gender Difference in Secular Trend in Sweden
- 2014
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Ingår i: Hormone Research in Paediatrics. 82 (suppl 1), s. 132. - : S. Karger AG. - 1663-2818 .- 1663-2826.
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Konferensbidrag (refereegranskat)abstract
- Background, objective and hypotheses: By using QEPS, a new mathematic growth model, different components of growth can be analyzed, comparing secular trends of prepubertal and pubertal growth in Swedish birth cohorts born 1974 and 1990. Materials and methods: Two birth cohorts followed to adult height (AH) born around 1974 (1691 boys; 1666 girls) and 1990 (1647 boys; 1501 girls) being healthy, Nordic and born term. A subpopulation of 1974 (1177 boys; 1168 girls) and 1990 (989 boys; 919 girls) with < 10 height measurements evenly distributed during growth phases, and high data quality was used for comparison. The different components of the QEPS-model: (Q)uadratic, (E)xponential, (P)ubertal, and (S)top function were estimated with corresponding maximum values at AH and tempo adjusting ‘time scale ratios’ of E and P. Multivariate regression analyses were used for explaining the variation of AH. Results: Both boys and girls born 1990 compared to those born 1974 had at birth an increased lengthSDS and weightSDS and during infancy a more rapid growth (shorter Etimescale). Boys -1990 had increased prepubertal growth (P= 0.0001 for Qmax, Qheightscale), their pubertal part of growth was not significantly changed. Their AHcm increased 1.3 from 180.4 to 181.7; the variation in AH was explained to 44% by mid parental height (MPH) and birth characteristics, to 72% by adding Qmax, to 75% by pubertal onset age and to 99% by Pmax. Girls -1990 had prepubertal growth increased (P=0.05 for Qmax, Qheightscale). Their pubertal gain was markedly increased (P=0.001 for Pmax; Pheightscale), and duration decreased whereas mean menarche age remained 12.8 years. AHcm increased 0.7 from 167.6 to 168.3. AH could be explained to 52% by MPH and birth characteristics, to 71% by adding Qmax, to 75% by pubertal onset, and to 99% by Pmax. Conclusion: In cohorts born 16-years apart; a secular trend with increased AHcm was found, 1.3 in boys, due to more prepubertal growth, 0.7 in girls, due to more pubertal growth, indicating gender specific underlying regulations.
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| 16. |
- Holmgren, Anton, et al.
(författare)
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Higher childhood BMI is associated with less pubertal gain
- 2015
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Ingår i: Obesity Facts (The European Journal of Obesity). - : S. Karger AG. - 1662-4025 .- 1662-4033.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Objective: Our objective was to investigate the impact of body mass index (BMI) in childhood on the pattern of growth during puberty. Methods: The longitudinally followed Grow up 1990 Gothenburg birth cohort, with growth data from birth until adult height was analyzed, using the QEPS growth model (describing total height as a combination of four mathematical functions; Quadratic -Q, Exponential -E, Pubertal -P and Stop –S, Fig 1.), for calculation of estimates for pubertal growth (1). Individual BMI-SDS values, from 3.5–8 years of age (n = 1908) were calculated for linear and subgroup analyses (low/normal- nw, overweight – ow, obese– ob), based on the IOTF 2012 reference. Results: Ow/ob children already at birth were heavier and grew faster in height in the pre pubertal period compared to nw, due to an increased Q function. Ow/ob children of both genders had 3.4–4.3 months earlier puberty, reduced growth during puberty, boys and girls had 3 cm and 2 cm, respectively, less pubertal gain from the specific pubertal growth function (P) compared to their nw peers. We saw a negative dose-response effect of childhood BMI on pubertal gain, across the whole BMI spectrum (Fig 2–3.). The adult height was not related to BMI in childhood. Conclusion: For the first time, the result of the present study has shown that; the higher the BMI is in childhood, the less is the pubertal gain. Higher childhood BMI was also associated with increased pre pubertal growth due to an increased Q-function and the resulting adult height was similar for ow/ob and nw children. Reference 1.Holmgren A et al.: Horm. res. in paed. 2013;80(suppl. 1):177.
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| 17. |
- Holmgren, Anton, et al.
(författare)
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Pubertal height gain is inversely related to peak BMI in childhood.
- 2017
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Ingår i: Pediatric research. - : Springer Science and Business Media LLC. - 1530-0447 .- 0031-3998. ; 81:3, s. 448-454
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundChildhood BMI may influence subsequent growth in height as well as the timing of puberty. The aim of the present study was to investigate associations between BMI in childhood and subsequent height gain/pubertal growth.MethodsLongitudinal growth data were used (GrowUp1990 Gothenburg cohort, n=1901). The QEPS growth-model was used to characterize height gain in relation to the highest BMISDS value between 3.5 and 8 years of age. Children were defined as overweight/obese (OwOb) or normal weight/underweight (NwUw), using the 2012 International Obesity Task Force criteria.ResultsA negative association between childhood BMISDS and pubertal height gain was observed. Already at birth, OwOb children were heavier than NwUw children, and had a greater height velocity during childhood. Onset of puberty was 3.5/3.0 months earlier in OwOb girls/boys, and they had 2.3/3.1cm less pubertal height gain from the QEPS-models specific P-function than NwUw children. Adult height was not related to childhood BMI.ConclusionWe found that pubertal height gain was inversely related to peak BMI in childhood. Higher childhood BMISDS was associated with more growth before onset of puberty, earlier puberty and less pubertal height gain, resulting in similar adult heights for OwOb and NwUw children.
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| 18. |
- Holmgren, Anton, et al.
(författare)
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The Pubertal Gain in Height is Inversely Related to BMI in Childhood
- 2015
-
Ingår i: Hormone Research in Paediatrics. ; 84:Supplement 1, s. 268-69
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background: Weight in childhood may influence the pubertal timing and pattern of growth. Objective: To investigate the impact of BMI in childhood on further growth, especially the specific pubertal pattern of growth. Method: The longitudinally followed GrowUpGothenburg1990 birth cohort, was analyzed using the QEPS growth model (Nierop et al. Horm Res in Ped.2013; 80(suppl 1):152–153) (describing total height as a combination of four mathematical functions; Quadratic – Q, Exponential – E, Pubertal – P and Stop – S). Individual BMISDS values, from 3.5–8 years of age were calculated for linear and subgroup analyses (low/normal – Lw/Nw, overweight/obese – Ow/Ob), based on the IOTF 2012 reference (Cole TJ, Lobstein T. Pediatric obesity. 2012; 7(4):284–94.). Results: Across the whole BMI range a negative dose-response effect of childhood BMI on pubertal gain (Pmax) was found. Already at birth Owob children were heavier, and they grew faster in height in the prepubertal period compared to Lw/Nw, as evidenced by an increased Q function. Owob children of both genders had earlier puberty (91–117 days), P = 0.0004, reduced growth during puberty, boys/girls 3.13/2.26 cm less pubertal gain P<0.0001, from the specific pubertal growth function (Pmax). The adult height was not related to BMI in childhood. Conclusion: The higher BMI in childhood, the faster the prepubertal growth, the earlier onset of puberty, the less pubertal gain. This was evident across the whole BMI-range, making weight status an important modifier of growth. Funding information: This work was supported by the Swedish Research Council (VR no 7509 and VR 2006-7777), VR/FORMAS/FORTE/VINNOVA (259-2012-38 and 2006-1624); EpiLife-TEENS research program, Pfizer AB, the Governmental Grants for University Hospital Research (ALF), the R&D Department, County of Halland, and the Foundation Växthuset for children.
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| 19. |
- Holmgren, Anton, et al.
(författare)
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The Specific Pubertal Height Gain is Higher in Boys as Well as in Children with Lower BMISDS
- 2016
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Ingår i: Hormone Research in Paediatrics. - 1663-2818 .- 1663-2826.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background: Growth in height during puberty can be described by the QEPS-model as a combination of continuous basal growth, QES, and a specific pubertal growth function, P. Objective and hypotheses: To study the relationship between childhood BMISDS and the prepubertal gain and pubertal gain related to growth functions from the QEPS-model. Method: The longitudinally followed GrowUpGothenburg 1990 birth cohort, was analyzed, by the QEPS-model. Individual maximal BMISDS values, from 3.5–8.0 years of age (n=1901) were calculated for linear and subgroup analyses, underweight (blue cross), normal (blue open circles), overweight (red open circles), obese (red circles). Results: For girls (Figure left), total pubertal gain (Tpubgain) depended more on QESgain during puberty. For boys, total pubertal gain depended more on specific Pgain (Figure right). With higher BMISDS this balance was shifted towards less Pgain for both girls and boys. Before puberty, children with higher BMISDS were taller, expressed as higher QESgain, with a linear correlation over the whole BMI–range (P<0.001for both girls/ boys). Conclusion: During puberty, girls grew more due to the QES than the P functions, with opposite findings in boys. For both boys and girls, there were less Pgain and more QES- gain with higher childhood BMISDS. Before puberty, children with higher BMISDS were taller.
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| 20. |
- Sjöberg, Agneta, 1956, et al.
(författare)
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Energy intake in Swedish adolescents: validation of diet history with doubly labelled water
- 2003
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Ingår i: Eur J Clin Nutr. ; 57:12, s. 1643-52
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To compare habitual energy intake (EI) estimated from diet history (DH) with total energy expenditure (TEE) measured with doubly labelled water (DLW) in adolescents. DESIGN: DH included a detailed questionnaire and an interview. TEE was measured during a 14-day period. Adequate (AR), under- (UR) and over-reporters (OR) were defined from the ratio EI/TEE: AR 0.84-1.16, UR <0.84 and OR >1.16. SETTING: Participants were recruited from grade 9 in a compulsory school in Goteborg, Sweden. All data were collected at school and DLW dosages were distributed at Sahlgrenska University Hospital. SUBJECTS: A total of 35 adolescents (18 boys, 17 girls), 15.7 (0.4) y. RESULTS: EI was 11.0 (3.6) MJ and TEE was 11.4 (2.1) MJ (P=0.42). DH was able to rank EI compared to TEE (Spearman's r=0.59, P< or =0.001). For girls, EI was 18% lower (P=0.0067) and for boys, EI was 7% higher (P=0.26) compared to TEE. The 95% limits of agreement for difference between TEE and EI were -5.6 to 6.5 MJ. In total, 20 subjects were defined as AR (57%), nine as UR (26%) and six as OR (17%). Energy from in-between meals was 33% lower (P=0.0043) in UR girls and 57% higher (P=0.026) in OR boys, compared to adequate reporting girls and boys, respectively. In UR girls, energy-adjusted intake (10 MJ) of specific foods did not differ significantly, fat was lower and carbohydrate and vitamin C were higher compared to AR girls (all P<0.05). OR boys had no significant differences in food and nutrient intake in 10 MJ compared to AR boys. CONCLUSION: The diet history was able to capture EI for the group and to rank subjects. There was a wide individual range in reporting-accuracy related to gender. SPONSORSHIP: The Ingabritt and Arne Lundberg Foundation, The Wilhelm and Martina Lundgren Foundation.
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| 21. |
- Sjöberg, Lars, 1947-
(författare)
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Arne Bjerhammar- a personal summary of his academic deeds
- 2021
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Ingår i: Journal of Geodetic Science. - : DE GRUYTER POLAND SP Z O O. - 2081-9919 .- 2081-9943. ; 11:1, s. 1-6
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Arne Bjerhammar is well known worldwide mainly for his research in physical geodesy but also for introducing a new matrix algebra with generalized inverses applied in geodetic adjustment. Less known are his developments in geodetic engineering and contributions to satellite and relativistic geodesy as well as studies on the relation between the Fennoscandia land uplift and the regional gravity low. Most likely part of his research has contributed to worldwide political relaxation during the cold war, which deed was honored by a certificate of achievement awarded by the Department of Research of the US army as well as the North Star Order by the King of Sweden. Arne Bjerhammar’s pioneer scientific production, in particular on a world geodetic system, towards what would become GPS, as well as relativistic geodesy, is still of great interest among the worldwide geodetic community, while the memories and spirit along his outstanding academic deeds have more or less fainted away from his home university (KTH) only a decade after he passed away.
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| 22. |
- Sjöberg, Lars, 1947-, et al.
(författare)
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Combination of three global Moho density contrast models by a weighted least-squares procedure
- 2022
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 16:4, s. 331-339
-
Tidskriftsartikel (refereegranskat)abstract
- Due to different structures of the Earth's crust and mantle, there is a significant density contrast at their boundary, the Moho Density Contrast (or shortly MDC). Frequently one assumes that the MDC is about 600 kg/m3, but seismic and gravimetric data show a considerable variation from region to region, and today there are few such studies, and global models are utterly rare. This research determines a new global model, called MDC21, which is a weighted least-squares combination of three available MDC models, pixel by pixel at a resolution of 1° × 1°. For proper weighting among the models, the study starts by estimating lacking standard errors and (frequently high) correlations among them. The numerical investigation shows that MDC21 varies from 21 to 504 kg/m3 in ocean areas and ranges from 132 to 629 kg/m3 in continental regions. The global average is 335 kg/m3. The standard errors estimated in ocean regions are mostly less than 40 kg/m3, while for continental regions it grows to 80 kg/m3. Most standard errors are small, but they reach to notable values in some specific regions. The estimated MDCs (as well as Moho depths) at mid-ocean ridges are small but show significant variations and qualities.
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| 23. |
- Sjöberg, Lars Erik, 1947-
(författare)
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Comments H. Schmidt's remarks on Sjöberg
- 2006
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Ingår i: Zeitschrift für Geodäsie, Geoinformation und Landmanagement. - Germany. - 1618-8950. ; 131:3, s. 155-
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Tidskriftsartikel (refereegranskat)
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| 24. |
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| 25. |
- Sjöberg, Lars Erik, 1947-
(författare)
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Local Least Squares Spectral Filtering and Combination by Harmonic Functions on the Sphere
- 2011
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Ingår i: Journal of Geodetic Science. - Poland : Versita. - 2081-9943 .- 2081-9919. ; 1:4, s. 355-360
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 26. |
- Sjöberg, Lars Erik, 1947-
(författare)
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On the Best Quadratic Minimum Bias Non-Negative Estimator of a Two-Variance Component Model
- 2011
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Ingår i: Journal of Geodetic Science. - Poland : Versita. - 2081-9943 .- 2081-9919. ; 1:3, s. 280-285
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Sjöberg, Lars Erik, 1947-
(författare)
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On the Definition and Realization of a Global Vertical Datum
- 2011
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Ingår i: Journal of Geodetic Science. - Poland : Versita. - 2081-9943 .- 2081-9919. ; 1:2, s. 154-157
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 28. |
- Sjöberg, Lars Erik, 1947-
(författare)
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Solving the Topographic Potential Bias as an Initial Value Problem
- 2009
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Ingår i: Artificial Satellites: journal of planetary geodesy. - Poland : Versita. - 0208-841X. ; 44:3, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- If the gravitational potential or the disturbing potential of the Earth be downward continued by harmonic continuation inside the Earth's topography, it will be biased, the bias being the difference between the downward continued fictitious, harmonic potential and the real potential inside the masses. We use initial value problem techniques to solve for the bias. First, the solution is derived for a constant topographic density, in which case the bias can be expressed by a very simple formula related with the topographic height above the computation point. Second, for an arbitrary density distribution the bias becomes an integral along the vertical from the computation point to the Earth's surface. No topographic masses, except those along the vertical through the computation point, affect the bias. (To be exact, only the direct and indirect effects of an arbitrarily small but finite volume of mass around the surface point along the radius must be considered.) This implies that the frequently computed terrain effect is not needed (except, possibly, for an arbitrarily small inner-zone around the computation point) for computing the geoid by the method of analytical continuation.
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| 29. |
- Sjöberg, Lars E., 1947-, et al.
(författare)
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The uncertainty of CRUST1.0 Moho depth and density contrast models
- 2021
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 15:2, s. 143-152
-
Tidskriftsartikel (refereegranskat)abstract
- As crustal structure models based on seismic and other data are frequently used as a-priori information for further geophysical and geological studies and interpretations (e. g., for gravity inversion), it is important to accurately document their qualities. For instance, the uncertainties in published crustal structures deeply affect the accuracies of produced Moho contour maps. The qualities in seismic crustal models arise from several factors such as the survey method, the spatial resolution of the survey (for example the spacing of the shot points and the recording stations), and the analytical techniques utilized to process the data. It is difficult to determine the uncertainties associated with seismic based crustal depth/Moho depth (MD) models, and even more difficult to use such data for estimating the Moho density contrast (MDC) and its accuracy. However, there is another important observable available today, namely global satellite gravitational data, which are fairly homogeneous v. r. t. accuracy and distribution over the planet. For instance, we find by simple error propagation, using the error covariance matrix of the GOCE TIM5 gravitational model, that this model can determine the MD to a global RMS error of 0.8 km with a resolution of about 1 degrees for a known MDC of 200 kg/m(3). However, the uncertainty in the MDC will further deteriorate the result. We present a new method for estimating the MD and MDC uncertainties of one model by comparing it with another (correlated or uncorrelated) model with known uncertainty. The method is applied in estimating the uncertainty for the CRUST1.0 MD model from four global models (CRUST19, MDN07, GEMMA1.0, KTH15C), yielding mean standard errors varying between 2 and 4.9 km in ocean regions and between 3.2 and 6.0 km on land regions with overall means of 3.8 +/- 0.4 and 4.8 +/- 0.6 km, respectively. Also, starting from the KTH15C MDC model, the mean standard error of CRUST1.0 MDC was estimated to 47.4 and 48.3 kg/m(3) for ocean and land regions, respectively.
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| 30. |
- Sjöberg, Lars E., 1947-
(författare)
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Unbiased least-squares modification of Stokes' formula
- 2020
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Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 94:9
-
Tidskriftsartikel (refereegranskat)abstract
- As the KTH method for geoid determination by combining Stokes integration of gravity data in a spherical cap around the computation point and a series of spherical harmonics suffers from a bias due to truncation of the data sets, this method is based on minimizing the global mean square error (MSE) of the estimator. However, if the harmonic series is increased to a sufficiently high degree, the truncation error can be considered as negligible, and the optimization based on the local variance of the geoid estimator makes fair sense. Such unbiased types of estimators, derived in this article, have the advantage to the MSE solutions not to rely on the imperfectly known gravity signal degree variances, but only the local error covariance matrices of the observables come to play. Obviously, the geoid solution defined by the local least variance is generally superior to the solution based on the global MSE. It is also shown, at least theoretically, that the unbiased geoid solutions based on the KTH method and remove–compute–restore technique with modification of Stokes formula are the same. © 2020, The Author(s).
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| 31. |
- Sjöberg, Lars, 1947-, et al.
(författare)
-
Estimation of Crustal Motions at the Permanent GPS Station SVEA, Antarctica from 2005 to 2009
- 2011
-
Ingår i: Journal of Geodetic Science. - : Walter de Gruyter GmbH. - 2081-9919 .- 2081-9943. ; 1:3, s. 215-220
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Tidskriftsartikel (refereegranskat)abstract
- Estimation of Crustal Motions at the Permanent GPS Station SVEA, Antarctica from 2005 to 2009: 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.
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| 32. |
- Sjöberg, Lars, 1947-
(författare)
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Geoid model validation and topographic bias
- 2022
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Ingår i: Journal of Geodetic Science. - : De Gruyter Open. - 2081-9919 .- 2081-9943. ; 12:1, s. 38-41
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Tidskriftsartikel (refereegranskat)abstract
- Recently a number of geoid campaigns were performed to verify different types of geoid and quasigeoid modeling techniques. Typically, GNSS-leveling was employed as an independent method, but in some cases zenith camera astronomic deflection data were also used in astrogeodetic determinations of the geoid and/or quasigeoid. However, due to the uncertainty in the topographic density distribution data (and thereby in orthometric heights), we conclude that neither GNSS-leveling nor astrogeodetic techniques can reliably verify differences between gravimetric geoid models at several centimeter levels in rough mountainous regions. This is because much the same topographic data are used both in the gravimetric geoid models and in their verifications by geometric and/or astrogeodetic geoid models. On the contrary, this is not a problem in verifying gravimetric quasigeoid models, as they are independent of the topographic density distribution, and so is the related normal height used in GNSS-leveling.
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| 33. |
- Sjöberg, Lars, 1947-, et al.
(författare)
-
Geoid or Quasi-Geoid? A Short Comparison
- 2024
-
Ingår i: X Hotine-Marussi Symposium on Mathematical Geodesy - Proceedings of the Symposium, 2022. - : Springer Nature. ; , s. 171-174
-
Konferensbidrag (refereegranskat)abstract
- This article is a short introduction to the debate on choosing the geoid and orthometric heights or the quasi-geoid and normal heights as the vertical coordinate system. It mainly compiles some more or less already known facts for comparing the two systems.
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| 34. |
- Sjöberg, Lars, 1947-, et al.
(författare)
-
MOHV21 : a least squares combination of five global Moho depth models
- 2022
-
Ingår i: Journal of Geodesy. - : Springer Nature. - 0949-7714 .- 1432-1394. ; 96:6
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to determine MOHV21, a Moho depth model based on an optimal combination of five global seismic and gravimetric-isostatic models of Moho depth by a weighted least squares approach at a resolution of 1° × 1°. For proper weighting among the data, the study starts with determining (mostly missing) standard errors and correlations among the models. The standard errors among the input models range from 1.0 (in Brazil) to 6.8 km (in Peru) and from 0.1 (in Huna Bay) to 6.0 km (in East Pacific Ridge) for Moho depth on land and ocean, respectively. The correlations among the five models range between − 0.99 and + 0.90. The Moho depths for MOHV21 at land regions vary between 14.5 (at the Horn of Africa) and 75 km (in the Himalayas) and between 6.6 (in the Greenland Sea) and 51.8 (in the Gulf of Bothnia) for land and ocean regions, respectively (However, note that, the Gulf of Bothnia belongs to continental crust, while the oceanic crust is generally within 20 km). The standard errors are generally within a few km but reaches 6.8 km (9%) in the highest mountains. The shallow Moho depths along mid-ocean ridges are well exposed in the model. Notable regional Moho highs are visualized in the Tarim basin in NW China of 59 ± 6.5 km and in Central Finland of 57 ± 4.7 km. A comparison of MOHV21 with a mosaic of regional models shows large differences reaching ± 25 km in Africa, Antarctic, and parts of S. America, while the differences are relatively modest in those parts of oceans that are available in the regional models.
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| 35. |
- Sjöberg, Lars, 1947-, et al.
(författare)
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On Gravity Inversion by No-Topography and Rigorous Isostatic Gravity Anomalies
- 2015
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Ingår i: Pure and Applied Geophysics. - : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136. ; 172:10, s. 2669-2680
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 36. |
- Sjöberg, Lars, 1947-
(författare)
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On the gravity and geoid effects of glacial isostatic adjustment in Fennoscandia : a short note
- 2015
-
Ingår i: Journal of Geodetic Science. - : Walter de Gruyter. - 2081-9919 .- 2081-9943. ; 5, s. 189-191
-
Tidskriftsartikel (refereegranskat)abstract
- Many geoscientists argue that there is a gravity low of 10-30 mGal in Fennoscandia as a remaining fingerprint of the last ice age and load, both vanished about 10 kyr ago. However, the extraction of the gravity signal related with Glacial Isostatic Adjustment (GIA) is complicated by the fact that the total gravity field is caused by many significant density distributions in the Earth. Here we recall a methodology originating with A. Bjerhammar 35 years ago, that emphasizes that the present land uplift phenomenon mainly occurs in the region thatwas covered by the ice cap, and it is highly correlated with the spectral window of degrees 10-22 of the global gravity field, whose lower limit fairly well corresponds to the wavelength that agrees with the size of the region. This implies that, although in principle the GIA is a global phenomenon, the geoid and gravity lows as well as the land upheaval in Fennoscandia are typically regional phenomena that cannot be seen in a global correlation study as it is blurred by many irrelevant gravity signals. It is suggested that a regional multi-regression analysis with a band-limited spectral gravity signal as the observable, a method tested already 2 decades ago, can absorb possible significant disturbing signals, e.g. from topographic and crustal depth variations, and thereby recover the GIA signal.
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| 37. |
- Sjöberg, Lars, 1947-
(författare)
-
On the topographic bias by analytical continuation in geoid determination
- 2023
-
Ingår i: Studia Geophysica et Geodaetica. - : Springer Nature. - 0039-3169 .- 1573-1626. ; 67:1-2, s. 27-38
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Tidskriftsartikel (refereegranskat)abstract
- We consider the topographic bias in gravimetric geoid determination when analytically downward continuing the disturbing potential from the Earth’s surface to sea level. The total bias is subdivided into those of the Bouguer shell or plate and the terrain. In this process, the potential of the Bouguer shell always has a downward continuation bias in the process, which increases with the square of the topographic height and typically exceeds 1–2 cm for elevations higher than 1 km. The main conclusion is that the terrain does not provide a potential bias except possibly for masses located inside a dome of height of about 0.4 times the height of the computation point, and base radius equal to the height of the computation point. This result implies that the potential of all terrain masses of arbitrary density located exterior to the Bouguer shell as well as those outside the dome are unbiasedly downward continued to sea level.
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| 38. |
- Sjöberg, Lars, 1947-, et al.
(författare)
-
Remarks on the Terrain Correction and the Geoid Bias
- 2024
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Ingår i: X Hotine-Marussi Symposium on Mathematical Geodesy - Proceedings of the Symposium, 2022. - : Springer Nature. ; , s. 3-5
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Konferensbidrag (refereegranskat)abstract
- The incomplete knowledge of the topographic density distribution causes a topographic bias in all gravimetric geoid determinations. This bias becomes critical in aiming for accurate geoid models in high mountainous regions. The bias can be divided into two components: the bias of the Bouguer shell (or Bouguer plate) and that of the remaining terrain. Starting from the known (disturbing) potential at the Earth’s surface, we study the possible location of the bias caused by incomplete reduction of the terrain masses in the computational process, We show that there is no such bias for terrain masses located exterior to the Bouguer plate/shell and/or inside the Bouguer plate at a lateral distance exceeding the height HP of the topography at the computational point. We conclude that the only possible terrain bias could be generated by masses inside a dome of height 2−1HP centered along the radius vector through the computational point with its base of radius HP at sea-level.
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| 39. |
- Sjöberg, Lars, 1947-
(författare)
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Rigorous geoid-from-quasigeoid correction using gravity disturbances
- 2015
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Ingår i: Journal of Geodetic Science. - : Walter de Gruyter GmbH. - 2081-9919 .- 2081-9943. ; 5:1, s. 115-118
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Tidskriftsartikel (refereegranskat)abstract
- We present rigorous solutions for the geoid-fromquasigeoid correction (GQC) using Taylor expansions of surface gravity disturbances along the vertical from the Earth's surface to the geoid. One solution takes advantage of the topographic potential bias at the geoid, which can be expressed by a simple formula. This implies that the accurate GQC does not need a terrain correction.
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| 40. |
- Sjöberg, Lars, 1947-
(författare)
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The development of physical geodesy during 1984-2014 : - a personal review
- 2015
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Ingår i: Journal of Geodetic Science. - : Walter de Gruyter. - 2081-9919 .- 2081-9943. ; 5, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- This article is a personal review of the development of physical geodesy during 1984-2014. The period is characterized by an intensive advance in both data and theory to meet the growing technical demands in GPS/GNSS applications and scientific needs in geoscience. As a result,many parts of theworld are nowmapped with a 1cmdetailed geoid model, and the global long- to mediumwavelengths of the gravity field and geoid are homogeneously determined to 1 mGal and 1 cm by satellite-only dedicated satellite gravity missions. The future can expect to see even higher demands for accuracy and reliability to satisfy the specifications for a pure geoid model based vertical datum.
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| 41. |
- Sjöberg, Lars, 1947-
(författare)
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The three Swedish kings of geodesy : Speech at the NKG General Assembly dinner in 2022
- 2023
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Ingår i: Journal of Geodetic Science. - : Walter de Gruyter GmbH. - 2081-9919 .- 2081-9943. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- During the 1950s-1970s, there were three geodesy professors in Sweden. Before and after that period the only such position was at KTH in Stockholm. One in the triple proposed the creation of the Nordic Geodetic Commission, which was realized in 1953 and still exists in much the same form as originally proposed.
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| 42. |
- Sjöberg, Lars, 1947-
(författare)
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The topographic bias in Stokes’ formula vs. the error of analytical continuation by an Earth Gravitational Model- are they the same?
- 2015
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Ingår i: Journal of Geodetic Science. - : Walter de Gruyter. - 2081-9919 .- 2081-9943. ; 5, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- Geoid determination below the topographic surface in continental areas using analytical continuation of gravity anomaly and/or an external type of solid spherical harmonics determined by an Earth GravitationalModel (EGM) inevitably leads to a topographic bias, as the true disturbing potential at the geoid is not harmonic in contrast to its estimates. We show that this bias differs for the geoid heights represented by Stokes’ formula, an EGMand for the modified Stokes formula. The differences are due to the fact that the EGM suffers from truncation and divergence errors in addition to the topographic bias in Stokes’ original formula.
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| 43. |
- Ågren, Jonas, 1919-, et al.
(författare)
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The new gravimetric quasigeoid model KTH08 over Sweden
- 2009
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Ingår i: Journal of Applied Geodesy. - Germany : de Gruyter. - 1862-9024. ; 3:3, s. 143-153
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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