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- Bergstrand, Sten, 1971, et al.
(författare)
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BIFROST: Noise properties of GPS time series
- 2007
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Ingår i: in "Dynamic Planet: Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic Tools", IAG Symposium, Cairns, Australia, 22-26 August, 2005, Series: International Association of Geodesy Symposia , Vol. 130, Tregoning, Paul; Rizos, Chris (Eds.), Springer. - 9783540493495 ; 130, s. 123-130
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Konferensbidrag (refereegranskat)
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| 2. |
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| 3. |
- Bergstrand, Sten, 1971, et al.
(författare)
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Geometric Variations of a Geodetic Radio Telescope
- 2017
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Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041104 ; , s. 61-64
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Bergstrand, Sten, 1971
(författare)
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GPS for Geophysics: Glacial Isostatic Adjustment and Tests of Ionospheric Models
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation is divided into two parts that separately utilize high precision Global Positioning System (GPS) satellite observations for inferences of solid earth and ionospheric parameters.In the first part of the dissertation, solid earth movements in Sweden and Finland are observed with GPS at a precision of the order 0.1 mm/yr.GPS is the first technique that is able to resolve the horizontal movements that are related to the post-glacial rebound or---more generally---glacial isostatic adjustment in the region and the longest baselines are found to be expanding at a rate of the order 3 mm/yr.These results are used for inferences of the viscosity of the mantle of the earth as well as the thickness of the elastically behaving lithosphere without the trade-off between these two parameters that affects observations of the vertical components.The upper mantle viscosity was found to be $ 5\times10^{20} $ Pa~s and the lithospheric thickness larger than 90 km.The position uncertainties for northern stations in the observing network have earlier been found to be larger than in the south due to winter-time snow coverage of the receiving antennas.A fractal model was therefore used in an evaluation of the underlying time series in order to derive realistic uncertainties of the individual velocity estimates.The spectral power of the time series were estimated directly from a smoothed power spectrum using uncorrelated bins and a new transform which normalizes the power spectrum variance.In the second part of the dissertation, the impact of the proposed ionospheric model for the coming European global navigation satellite system Galileo is investigated.A non-physical equivalent sunspot number was used as an input parameter to optimize the global response of the model.Simulations indicate an ionospheric model misfit on single-frequency receiver position estimates generally less than 3 m, with better fits for mid-year months and intermediate to high latitude geomagnetic regions and worse fits for regions associated with the ionospheric equatorial anomaly.An investigation that exploited the multi-layered formulation of the model indicates an improvement with a model change for stand-alone users as well as for surveyors with network real time kinematic abilities.
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| 6. |
- Bergstrand, Sten, 1971, et al.
(författare)
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Ionospheric Corrections for Accurate Positioning in Real Time
- 2005
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Ingår i: in Proc. Radio Science and Communication (RVK), eds. O. Gustafsson, P. Löwenborg, Linköping, Sweden, June 14-16, 2005. - 9170561222 ; , s. 391-394
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
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| 8. |
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| 9. |
- Kallio, Ulla, et al.
(författare)
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Automated Simultaneous Local Ties with GNSS and Robot Tacheometer
- 2016
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Ingår i: IVS 2016 General Meeting Proceedings "New Horizons with VGOS". Edited by Dirk Behrend, Karen D. Baver, and Kyla L. Armstrong, NASA/CP-2016-219016, 2016. ; :NASA/CP-2016-219016, s. 154-158
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Westlund, Karin, et al.
(författare)
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EVALUATION OF NAVIGATION SATELLITE SYSTEMS FOR FORESTRY AND ITS PRECISION IN A FOREST ENVIRONMENT
- 2012
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Ingår i: Proceedings of FORMEC 2012: Forest Engineering - Concern, Knowledge and Accountability in Today’s Environment.
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Konferensbidrag (refereegranskat)abstract
- The Swedish forestry industry is dependent of reliable positioning in the forest since much of the information in the supply chain carries positioning data. Correct coordinates are needed for the survey of the site, information of the harvesting and forwarding progress as well as positioning of road side inventory. The position data should also be able to save e.g. for planning purposes to be used throughout the forest production life-cycle. One way of providing position data is through the use of Global Navigation Satellite Systems (GNSS) where the most accurate equipment and strategies provide positions of order 1 cm accuracy in fair conditions. The GNSS equipment currently being used on the machines in the forest is however often more basic equipment that at best may provide accuracies of order 10 m under the same conditions, and often worse. In addition to the antenna, receiver and other technical equipment many factors affect the positioning quality; the forest environment itself causes uncertainty in the positioning due to tree trunk blockage of signal paths, reflections from trees, etc. Currently there are two operating GNSS systems: the American GPS and the Russian GLONASS systems. Today only GPS is being used, but with more systems emerging in the near future (e.g. the European Galileo system) the availability of satellite signals for positioning will increase significantly in the forest environment. The aim of the project is to evaluate the current accuracy of the positioning as well as compare stand-alone GPS with multiple GNSS system solutions in the forest environment. The project will also suggest techniques for improving the accuracy and robustness of the positioning suitable for the forestry field of application. The project will contribute with improvements of information flows through the whole value chain, making use of reliable positioning data. It will also provide input for ICT based systems to increase logging efficiency and minimize ground and soil impacts. Additionally, costs through misleading positioning in timber transport will be reduced and the traceability of timber and forest products will improve. The project will be ongoing during spring and finalized during the summer 2012.
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