| 1. |
- Appleby, Graham, et al.
(author)
-
GGOS Requirements for Core Sites
- 2015
-
Reports (peer-reviewed)abstract
- The Global Geodetic Observing System, an entity under the International Association of Geodesy (IAG) has undertaken the task of advocating for the geodetic infrastructure necessary to meet the global change and other societal challenges, and defining the requirements for the geodetic observatories that constitute it. In this role, GGOS will work with the IAG Measurement Services, the scientific Community, and national and international agencies to bring a combined effort to bear on these areas of international concern. A major task within this effort is the upgrading, expansion, and maintenance of the global ground network of co-located Core Sites for geodesy to enable the realization and maintenance of the International Terrestrial Reference Frame (ITRF), Earth orientation parameters and precision orbits to meet the needs of Earth orbiting missions, Earth Surface and interior programs, and deep space navigation. GGOS and the geodetic Core Sites should be compliant with the UN resolution from Feb 26, 2015. See http://www.unggrf.org/. This Site Requirements Document outlines what is needed for that compliance.
|
|
| 2. |
- Bergstrand, Sten, et al.
(author)
-
A gravitational telescope deformation model for geodetic VLBI
- 2019
-
In: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 93:5, s. 669-680
-
Journal article (peer-reviewed)abstract
- We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.
|
|
| 3. |
- Bergstrand, Sten, et al.
(author)
-
Activities of the IERS Working Group on Site Survey and Co-location
- 2016
-
In: International VLBI Service for Geodesy and Astrometry 2016 General Meeting Proceedings. - Greenbelt, MD : National Aeronautics and Space Administration. ; , s. 113-117
-
Conference paper (other academic/artistic)abstract
- The objective of the International Earth Rotation and Reference Systems Service (IERS) Working Group on Site Survey and Co-location is to improve local measurements at space geodesy sites. We appointed dedicated Points of Contact (POC) with the four different services of IERS as well as the NASA Space Geodesy Project in order to improve the efficiency of internal communication within the working group. Following the REFAG2014 conference, the POCs agreed on a common and general terminology on local ties that clarifies the communication regarding site surveying and co-location issues between and within the IERS services. We give brief introductions to the different observation techniques and mention some contemporary issues related to site surveying and co-location.
|
|
| 4. |
- Bergstrand, Sten, 1971, et al.
(author)
-
BIFROST: Noise properties of GPS time series
- 2007
-
In: 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
-
Conference paper (peer-reviewed)
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Bergstrand, Sten, 1971, et al.
(author)
-
Geometric Variations of a Geodetic Radio Telescope
- 2017
-
In: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041104 ; , s. 61-64
-
Conference paper (other academic/artistic)
|
|
| 9. |
- Bergstrand, Sten, 1971
(author)
-
GPS for Geophysics: Glacial Isostatic Adjustment and Tests of Ionospheric Models
- 2006
-
Doctoral thesis (other academic/artistic)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.
|
|
| 10. |
|
|
