| 1. |
- Poutanen, Markku, et al.
(författare)
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The Nordic Geodetic Observing System (NGOS)
- 2007
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Ingår i: International Association of Geodesy Symposia, Dynamic Planet. ; , s. 749-756
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Nordic Geodetic Observing System (NGOS) integrates fundamental geodetic techniques for the long-term observation of Earth system parameters. The Nordic Geodetic Commission (NKG) established a Task Force with the mission to prepare a document providing the definition and draft for the implementation of the NGOS.The regional system aligns with international efforts such as the Global Earth Observation System of Systems (GEOSS) and Global Observing Systems and adheres to the Integrated Global Observing Strategy (IGOS). Recent developments in the structure and function of the International Association of Geodesy cumulated in the establishment of the Global Geodetic Observing System, GGOS. NGOS is planned as a regional implementation and densification of the GGOS.The NGOS is proposed as a system that will serve a wide range of scientific and practical applications. For the Nordic countries, a main focus will be on crustal motion, dynamics of glaciated areas and sea level. NGOS aims to provide geodetic observations for the Nordic area that are of sufficient quantity and quality to serve most of the needs of global Earth observation as well as practical and scientific applications in the region. In particular, NGOS will contribute to the GGOS and other IAG Services; European activities such as EUREF, ECGN, EUVN, and ESEAS; provide the reference frames for the Nordic countries, as well as contribute to the global ones; support scientific projects related to the geodynamics of the Nordic area and provide ground-truth for satellite missions. In this paper we describe the plans and current status of the NGOS.
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| 2. |
- 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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| 3. |
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| 4. |
- Bock, Dagmar, et al.
(författare)
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Atmospheric pressure loading displacement of SLR stations
- 2005
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 39:3, s. 247-266
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the local displacement at ground stations of the world-wide Satellite Laser Ranging (SLR) network induced by atmospheric pressure variations. Since currently available modelling options do not satisfy the requirements for the target application (real-time availability, complete coverage of SLR network), a new representation is developed. In a first step, the 3-dimensional displacements are computed from a 6-hourly grid of 1°×1° global pressure data obtained from the ECMWF, for the period 19972002. After having been converted into pressure anomalies, this pressure grid is propagated into horizontal and vertical station displacements using Greens functions and integrating contributions covering the entire globe; oceans are assumed to follow the inverted barometer (IB) approximation. In the next step, a linear regression model is developed for each station that approximates the time-series of the predicted vertical displacements as well as possible; this regression model relates the vertical displacement of a particular station to the local (and instantaneous) pressure anomaly. It is shown that such a simple model may represent the actual vertical displacements with an accuracy of better than 1 mm; horizontal displacements are shown to be negligible. Finally, the regression model is tested on actual SLR data on the satellites LAGEOS-1 and LAGEOS-2, covering the period January 2002 until April 2003 (inclusive). Also, two model elements are shown to be potential risk factors: the global pressure field representation (for the convolution method) and the local reference pressure (for the regression method). The inclusion of the atmospheric pressure displacement model gives improvements on most of the elements of the computations, although the effects are smaller than expected since the nominal effect is absorbed by solved-for satellite parameters.
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| 5. |
- Bos, Machiel, 1960, et al.
(författare)
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Computations of Green's Functions for Ocean Tide Loading
- 2012
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Ingår i: Sciences of Geodesy-II. - Berlin, Heidelberg : Springer Berlin Heidelberg. ; 9783642280009, s. 1-52
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Earth deforms periodically due to the varying weight of the ocean tides. Classical terrestrial geodetic techniques such as gravimetry, strain and tilt observe this deformation clearly. Also space geodetic techniques have reached an accuracy level where this loading signal can no longer be ignored. We present here the basic physical assumptions that underlie, and the derivation of, the mathematical framework that is used nowadays to compute these deformations. Special attention has been paid to the definition of the boundary conditions, how to treat the fluid core and the peculiarities that surround the deformation of the solid Earth at degree one. Also a short explanation of the Longman-Paradox is given. Finally, we discuss numerical methods to solve the differential equations and how to form the Green's functions that describe the ocean tide loading due to a point load.
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| 6. |
- Elgered, Gunnar, 1955, et al.
(författare)
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GNSS for global environmental Earth observation
- 2013
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This booklet is produced within the Gfg2 project, a three year coordination action, funded by the 7th Framework Program of the European Commission under the Environment theme. Its mission is to better assess the value of Global Navigational Satellite Systems (GNSS) for Global Environmental Earth Observation (GEEO) and GEOSS.
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| 7. |
- Elgered, Gunnar, 1955, et al.
(författare)
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GNSS för globala jordobservationer
- 2014
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Detta häfte har producerats av Gfg2-projektet, en treårig koordineringsaktivitet finansierad av Europeiska kommissionens sjunde ramprogram inom dess miljötema. Projektets uppgift är att belysa värdet av jordobservationer med hjälp av globala navigationssystem (GNSS = Global Navigational Satellite Systems) för Global Environmental Earth Observation (GEEO) och Global Earth Observation System of Systems (GEOSS).
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| 8. |
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| 9. |
- Freier, Christian, et al.
(författare)
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Mobile quantum gravity sensor with unprecedented stability
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 723:1, s. Art. no. 012050-
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Konferensbidrag (refereegranskat)abstract
- Changes of surface gravity on Earth are of great interest in geodesy, earth sciencesand natural resource exploration. They are indicative of Earth system's mass redistributions andvertical surface motion, and are usually measured with falling corner-cube- and superconductinggravimeters (FCCG and SCG). Here we report on absolute gravity measurements with amobile quantum gravimeter based on atom interferometry. The measurements were conductedin Germany and Sweden over periods of several days with simultaneous SCG and FCCGcomparisons. They show the best-reported performance of mobile atomic gravimeters todate with an accuracy of 39 nm/s^2, long-term stability of 0,5 nm/s^2 and short-term noise of 96 nm/s^2/(Hz)^1/2. These measurements highlight the unique properties of atomic sensors. Theachieved level of performance in a transportable instrument enables new applications in geodesyand related Fields, such as continuous absolute gravity monitoring with a single instrument underrough environmental conditions.
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| 10. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Contributions of Onsala Space Observatory to GGOS
- 2015
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Ingår i: Proceedings of the 22nd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789892061917 ; , s. 125-129
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 11. |
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| 12. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Analysis Center
- 2009
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Ingår i: International VLBI Service for Geodesy and Astrometry 2008 Annual Report, edited by D. Behrend and K. Baver. ; NASA/TP-2009-214183, s. 295-298
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We briefly summarize the activities of the IVS Analysis Center at the Onsala Space Observatory during 2008 and give examples of results of ongoing work.
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| 13. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory - IVS Analysis Center
- 2012
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Ingår i: International VLBI Service for Geodesy and Astrometry 2011 Annual Report, edited by K. D. Baver and D. Behrend. ; :NASA/TP-2012-217505, s. 249-251
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This report briefly summarizes the activities of the IVS Analysis Center at the Onsala Space Observatory during 2011 and gives examples of results of ongoing work.
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| 14. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Analysis Center
- 2013
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Ingår i: International VLBI Service for Geodesy and Astrometry 2012 Annual Report. ; , s. 298-301
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This report briefly summarizes the activities of the IVS Analysis Center at the Onsala Space Observatory during 2012 and gives examples of results of ongoing work.
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| 15. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Analysis Center
- 2011
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Ingår i: International VLBI Service for Geodesy and Astrometry 2010 Annual Report, edited by D. Behrend and K.Baver. ; :NASA/TP-2011-215880, s. 240-243
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We briefly summarize the activities of the IVS Analysis Center at the Onsala Space Observatory during 2010 and give examples of results of ongoing work.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory - IVS Network Station
- 2012
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Ingår i: International VLBI Service for Geodesy and Astrometry 2011 Annual Report, edited by K. D. Baver and D. Behrend. ; :NASA/TP-2012-217505, s. 88-91
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- During 2011 we contributed to 38 IVS sessions, including the CONT11 campaign. We used the majority of the sessions that involved both Onsala and Tsukuba to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. In particular, the whole CONT11 campaign was operated in ultra-rapid mode. Furthermore, we observed one additional one-baseline ultra-rapid dUT1 session, a three-station ultra-rapid EOP-session, the Venus Express space probe, and the RadioAstron satellite.
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| 20. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station
- 2013
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Ingår i: International VLBI Service for Geodesy and Astrometry 2012 Annual Report. ; , s. 130-133
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- During 2012 we participated in 40 IVS sessions. As in the previous four years, we used the majority of the sessions that involved both Onsala and Tsukuba to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. We observed one four-station ultra-rapid EOP session together with Tsukuba, Hobart, and HartRAO. We also observed the RadioAstron satellite and several GLONASSsatellites using the Onsala 25 m telescope.The highlight in 2012 was that our proposal to the Knut and Alice Wallenberg Foundation to establish a twin-telescope system at Onsala in accordance with the VLBI2010 recommendations was accepted.
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| 21. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory - IVS Network Station
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- During 2010 the Onsala Space Observatory contributed as an IVS Network Station to 27 VLBI sessions organized by the IVS. We used the majority of these sessions to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. Furthermore, we observed several additional one-baseline ultra-rapid dUT1 sessions. This report briefly summarizes the activities during the year 2010.
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| 22. |
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| 23. |
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| 24. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station Activities during 2014
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We participated in 39 IVS sessions, includ-ing CONT14. Eleven out of the initially planned ses-sions could not be observed due to the installation ofa new radome for the 20-m radio telescope. As in theprevious six years, we used several of the sessions thatinvolved both Onsala and Tsukuba to perform ultra-rapid UT1-UTC sessions together with our colleaguesin Tsukuba. This included the complete CONT14 cam-paign where near real-time UT1-UTC on the baselineOnsala—Tsukuba could be determined. The procure-ment of the telescopes for the Onsala Twin Telescopeswas started in the summer of 2014. The contract to buytwo VGOS radio telescopes was signed at the end of the year.
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| 25. |
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| 26. |
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| 27. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station Activities During 2021–2022, in International VLBI Service for Geodesy and Astrometry 2021+2022 Biennial Report, edited by K. L. Armstrong, D. Behrend, and K. D. Baver, NASA/TP-20230014975
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- During 2021 and 2022 we participated in a total of 81 IVS 24-hour legacy S/X sessions with the Onsala 20-m telescope. We observed in a total of 73 VGOS 24-hour sessions with one or both of the Onsala twin telescopes (OTT) in 2021 and 2022. In total we observed 114 VGOS one-hour Intensive sessions during 2021 and 2022, the majority together with the partner station Ishioka in Japan, but also five with Kokee Park. More than 50 % of these sessions involved both Onsala twin telescopes.We also performed 22 local interferometry measurements at Onsala during 2021 and 2022 for measuring the local ties between our telescopes that are used for geodetic VLBI. In 2021 we also performed 91 short (20-minute) flux-monitoring sessions with the OTT as a standalone instrument.
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| 28. |
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| 29. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Periodic station motion in Gothenburg observed with GPS - possibily related to hydrological phenomena?
- 2009
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Ingår i: Advances in Geosciences: Volume 13: Solid Earth (SE). - : World Scientific Publishing Co. Pte. Ltd.. - 9789812836175 ; 13:Solid Earth, s. 181-192
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- We analyze several years of GPS data recorded with roof-top stations in Gothenburg (Sweden) and permanent stations of the Swedish national reference network in the larger Gothenburg region. The derived station positions of several of the roof-top stations in Gothenburg reveal periodic horizontal motions with amplitudes of several millimeters and periodic vertical motions with amplitudes of up to 1.5 mm. The observed motions have primarily an annual period. We compare the GPS-derived station motions with hydrological information (ground water and river level) and meteorological information (air temperature and pressure). The results indicate that the GPS-detected motions might be related to hydrological phenomena.
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| 30. |
- Haas, Rüdiger, 1966, et al.
(författare)
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The IVS Analysis Center at the Onsala Space Observatory
- 2007
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Ingår i: International VLBI Service for Geodesy and Astrometry 2006 Annual Report, edited by D. Behrend and K. Baver, NASA/TP-2007-214151. ; , s. 224-227
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 31. |
- Haas, Rüdiger, 1966, et al.
(författare)
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The IVS Analysis Center at the Onsala Space Observatory
- 2006
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Ingår i: IVS 2005 Annual Report, NASA/TP-2006-214136. ; , s. 260-263
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This report briefly summarizes the activities of the IVS Analysis Center at the Onsala Space Observatory during 2005. Some examples of achieved results and ongoing analyses are presented.
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| 32. |
- Haas, Rüdiger, 1966, et al.
(författare)
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The IVS Analysis Center at the Onsala Space Observatory
- 2008
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Ingår i: International VLBI Service for Geodesy and Astrometry 2007 Annual Report, edited by D. Behrend and K. Baver. ; NASA/TP-2008-214162, s. 228-231
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 33. |
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| 34. |
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| 35. |
- Johansson, Jan, 1960, et al.
(författare)
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Continuous GPS measurements of postglacial adjustment in Fennoscandia - 1. Geodetic results
- 2002
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 107:B8
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Tidskriftsartikel (refereegranskat)abstract
- Project BIFROST (Baseline Inferences for Fennoscandian Rebound Observations, Sea-level, and Tectonics) combines networks of continuously operating GPS receivers in Sweden and Finland to measure ongoing crustal deformation due to glacial isostatic adjustment (GIA). We present an analysis of data collected between August 1993 and May 2000. We compare the GPS determinations of three-dimensional crustal motion to predictions calculated using the high-resolution Fennoscandian deglaciation model recently proposed by Lambeck et al. [1998a, 1998b]. We find that the maximum observed uplift rate (~10 mm/yr) and the maximum predicted uplift rate agree to better than 1 mm yr-1. The patterns of uplift also agree quite well, although significant systematic differences are evident. The root-mean-square residual rate for a linear error model yields estimates of rate accuracy of 0.4 mm/yr for east, 0.3 mm/yr for north, and 1.3 mm/yr for up; these figures incorporate model errors, however. We have also compared the values for the observed radial deformation rates to those based on sea level rates from Baltic tide gauges. The observational error for the vertical GPS rates required to give a reduced chi^2 of unity is 0.8 mm/yr. The time series do exhibit temporal variations at seasonal frequencies, as well as apparent low-frequency noise. An empirical orthogonal function analysis indicates that the temporal variations are highly correlated among the sites. The correlation appears to be regional and falls off only slightly with distance. Some of this correlated noise is associated with snow accumulation on the antennas or, for those antennas with radomes, on the radomes. This problem has caused us to modify the radomes used several times, leading to one of our more significant sources of uncertainty.
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| 36. |
- Lidberg, Martin, 1964, et al.
(författare)
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An improved and extended GPS-derived 3D velocity field of the glacial isostatic
- 2007
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Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 81:3, s. 213-230
-
Tidskriftsartikel (refereegranskat)abstract
- We present a new GPS-derived 3D velocity field for the Fennoscandia glacial isostatic adjustment (GIA) area. This new solution is based upon 3,000 days of continuous GPS observations obtained from the permanent networks in Fennoscandia. The period encompasses a prolongated phase of stable observation conditions after the northern autumn of 1996. Several significant improvements have led to smaller uncertainties and lower systematic errors in the new solutions compared to our previous results. The GPS satellite elevation cut-off angle was lowered to 10°, we fixed ambiguities to integers where possible, and only a few hardware changes occurred over the entire network. The GAMIT/GLOBK software package was used for the GPS analysis and reference frame realization. Our new results confirmed earlier findings of maximum discrepancies between GIA models and observations in northern Finland. The reason may be related to overestimated ice-sheet thickness and glaciation period in the north. In general, the new solutions are more coherent in the velocity field, as some of the perturbations are now avoided. We compared GPS-derived GIA rates with sea-level rates from tide-gauge observations, repeated precise leveling, and with GIA model computations, which showed consistency. © Springer-Verlag 2006.
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| 37. |
- Lidberg, Martin, 1964, et al.
(författare)
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Geodetic reference frames in the presence of crustal deformations - with focus on Nordic conditions
- 2008
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Ingår i: Report on the symposium of the IAG sub commission for Europe (EUREF), Riga, June 14-17, 2006, eds. J.A. Torres, H. Hornik, EUREF publication no. 16, Mitteilungen des Bundesamtes für Kartographie und Geodäsie, Frankfurt am Main 2008. - 1436-3445. - 3898888452 ; 40, s. 189-198
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 38. |
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| 39. |
- Lidberg, Martin, 1964, et al.
(författare)
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Recent results based on continuous GPS observations of the GIA process in Fennoscandia from BIFROST
- 2010
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 50:1, s. 8-18
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Tidskriftsartikel (refereegranskat)abstract
- We present the latest 3D velocity field of the Fennoscandian glacial isostatic adjustment (GIA) processfrom BIFROST. It is derived from more than 4800 days (13 years) of data at more than 80 permanentGPS sites. We use the GAMIT/GLOBK and the GIPSY/OASIS II software packages for GPS analysis andcompare the results. The solution has an internal accuracy at the level of 0.2 mm/year (1 sigma) forhorizontal velocities at the best sites.Wealso present a revised GIA prediction model. At the best sites, theoptimal model agrees with the observations to within 0.4 mm/year. However, the model systematicallyoverpredicts the magnitude of horizontal rates in the north. We discuss limitations in computed andpresented GNSS station velocities, where especially possible instability over time causing non-linearpattern in vertical time series are considered. In extension, preliminary results from an investigationapplying revised analysis strategies on a sparse subset of the database are presented, indicating possibleimprovements for the future.
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| 40. |
- Löfgren, Johan, 1983, et al.
(författare)
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Remote Sensing of the Coastal Ocean with Standard Geodetic GNSS-Equipment
- 2012
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Ingår i: European Geosciences Union General Assembly 2012, 22-27 April, Vienna, Austria.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We use standard geodetic Global Navigation Satellite System (GNSS) equipment to perform remote sensing measurements of the coastal ocean. This is done by a so-called GNSS-based tide gauge that uses both direct GNSS-signals and GNSS-signals that are reflected off the sea surface. Our installation is located at the Onsala Space Observatory (OSO) at the west coast of Sweden and consists of a zenith-looking Right Hand Circularly Polarized (RHCP) and a nadir-looking Left Hand Circularly Polarized (LHCP) antenna. Each antenna is connected to a standard geodetic-type GNSS-receiver.We applied two different analysis strategies to our GNSS data set. The first strategy is based on a traditional geodetic differential analysis [Löfgren et al., 2011] and makes use of the data from both receivers; connected to the zenith and the nadir looking antennae. This approach results in local sea level that is automatically corrected for land motion, meaning that the GNSS-based tide gauge can provide reliable sea-level estimates even in tectonic active regions. The second strategy focuses on the Signal-to-Noise Ratio (SNR) recorded with the receiver connected to the zenith-looking antenna [Larson et al., 2011]. The SNR is affected by multipath originating from the sea surface reflections. Analysis of the SNR data allows to determine the distance between the antenna and the reflecting surface, and thus to measure sea surface height. Results from both analysis strategies are compared to independently observed sea-level data from two stilling-well gauges operated by the Swedish Meteorological and Hydrological Institute (SMHI), which lie in a distance of several km from OSO. The root-mean-square agreement between the different time series of several month's length is on the order of 5 cm and better. These results indicate the large potential for using coastal GNSS-sites for the monitoring of the coastal ocean.References:Löfgren J.S., Haas R., Scherneck H-G., Bos M.S., (2011), Three months of local sea level derived from reflected GNSS signals, Radio Science, 46 (RS0C05).Larson K., Löfgren J.S., Haas R., (2011), The GPS tide gauge problem revisited, AGU Fall Meeting, 5-9 December, San Francisco, USA, Poster.
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| 41. |
- Löfgren, Johan, 1983, et al.
(författare)
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Sea-Level Analysis Using 100 Days of Reflected GNSS Signals
- 2011
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Ingår i: Proceedings of the 3rd International Colloquium - Scientific and Fundamental Aspects of the Galileo Programme, 31 August - 2 September 2011, Copenhagen, Denmark. ; :WPP 326, s. 5-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Global Navigation Satellite System (GNSS) signals reflected off the sea surface can be used for remote sensing of the sea level. We present results from a GNSS-based tide gauge using standard geodetic-type GNSS receivers for receiving both the reflected and the direct GNSS signals. The local sea level is then obtained using relative geodetic processing of the carrier phase delay.We show results from our analysis of 100 days of GNSS data from the Onsala Space Observatory (OSO). The GNSS-derived sea level is compared to a weighted average of sea level observations from two stilling well gauges located 18 km and 33 km away from OSO. The comparison shows a high level of agreement with a correlation coefficient of 0.96. Furthermore, the standard deviation (1σ) between the time series is 5.0 cm and the pairwise mean difference is 3.6 cm.Additionally, we present a tidal analysis of the three sea level datasets and compare the derived tidal constituents both to each other and to a Regional Tide Model (RTM). From the GNSS-derived sea level we find significant ocean tidal signals with reasonable amplitudes and with most phases in between those for the stilling well gauges sites. The comparison to the RTM shows limitations of the model for long-period tidal signals.
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| 42. |
- Löfgren, Johan, 1983, et al.
(författare)
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Sea Level Derived from Reflected GNSS Signals
- 2011
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Ingår i: American Geophysical Union Fall Meeting 2011, 5-9 December, San Francisco, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The traditional way to observe sea level is to use tide gauges, resulting in measurements relative to the Earth’s crust. However, in order to measure the sea-level change due to changes in ocean water volume and/or other oceanographic phenomena, all types of crustal motion at the measurement site need to be known.We present a remote sensing technique for measuring local sea level using standard geodetic-type Global Navigation Satellite System (GNSS) receivers. The installation consists of a zenith-looking Right Hand Circular Polarized (RHCP) antenna, receiving the direct signals, and a nadir-looking Left Hand Circular Polarized antenna, receiving the signals reflected of the sea surface. Each antenna is connected to a receiver and the antenna pair is deployed back-to-back at a coastal site. Estimating the vertical baseline between thetwo antennas, using standard geodetic analysis, the local sea level and its temporal variations can be determined. The advantage of this technique is that it allows to measure both sea surface height changes with relative positioning and land surface height changes, e.g., by precise point positioning of the RHCP antenna. Furthermore, the combined measurements of local sea level are automatically corrected for land motion, meaning that this installation could provide continuously reliable sea-level estimates in tectonic active regions.This GNSS-based tide gauge has been operating continuously at the Onsala Space Observatory (OSO) on the west coast of Sweden since September 2010. We present results from several months of operations and compare them to sea-level measurements from two stilling well gauges about 18 km south and 33 km north of OSO. We find a high degree of agreement between the time series with correlation coefficients of larger than 0.95. The root-mean-square differences between the GNSS-derived sea level and the stilling well gauge measurements are 5.9 cm and 5.5 cm, which is lower than between the two stilling well (6.1 cm). Furthermore, we present a tidal analysis of the three independent sea level time series and compare the derived tidal constituents among each other and with respect to theoretical models.
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| 43. |
- Löfgren, Johan, 1983, et al.
(författare)
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Sea Level Records from Geodetic GPS Receivers: a New Coastal Sea Level Dataset
- 2012
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Ingår i: American Geophysical Union (AGU) Fall Meeting, 3-7 December 2012, San Francisco.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Global sea level rise and local sea level variations due to climate change has the potential for a significant impact on coastal societies. Thus, it is of great importance to monitor and understand how the sea level is changing. Existing techniques to measure sea level have provided important insights in this field during the last decades. However, further observations are necessary in order to fully understand the underlying processes.We present the possibility of a new coastal sea level dataset based on analysis of Signal-to-Noise Ratio (SNR) data from existing permanent GPS stations at the coast. For a GPS antenna close enough to the ocean, the multipath signals, reflected off the sea surface, interfere with the direct satellite signals. This becomes especially visible as oscillations in the recorded SNR data. The analysis of the SNR oscillations provides the distance between the sea surface and the GPS antenna phase center. Thus, such an installation can be called a GPS tide gauge and can be used to monitor sea level.The advantage of a GPS tide gauge is that it allows both determination of the sea level and determination of the position with respect to the International Terrestrial Reference Frame, using a single geodetic instrument. This is particularly valuable in areas with land surface motion where the usefulness of traditional tide gauges is restricted.The technique has been verified through comparison to traditional tide gauges at two sites. The comparison of more than three months long time series resulted in correlationcoefficients of better than 0.97 for both sites. For the station with low and high tidal range, the root-mean-square agreement between the GPS results and the tide gauge records were better than 5 and 10 cm, respectively.In this presentation we show preliminary results for sea level records world wide by applying this technique to several existing permanent GPS stations.
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| 44. |
- Löfgren, Johan, 1983, et al.
(författare)
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Sea level time series and ocean tide analysis from multipath signals at five GPS sites in different parts of the world
- 2014
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 80, s. 66-80
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Tidskriftsartikel (refereegranskat)abstract
- We present sea level observations derived from the analysis of signal-to-noise ratio (SNR) data recorded by five coastal GPS stations. These stations are located in different regions around the world, both in the northern and in the southern hemisphere, in different multipath environments, from rural coastal areas to busy harbors, and experience different tidal ranges.The recorded SNR data show periodic variations that originate from multipath, i.e. the interference of direct and reflected signals. The general assumption is that for satellite arcs facing the open sea, the rapid SNR variations are due to reflections off the sea surface. The SNR data recorded from these azimuth intervals were analyzed by spectral analysis with two methods: a standard analysis method assuming a static sea level during a satellite arc and an extended analysis method assuming a time dependent sea level during a satellite arc.The GPS-derived sea level results are compared to sea level records from co-located traditional tide gauges, both in the time and in the frequency domain. The sea level time series are highly correlated with correlation coefficients to the order of 0.89–0.99. The root-mean-square (RMS) difference is 6.2 cm for the station with the lowest tidal range of 165 cm and 43 cm for the station with the highest tidal range of 772 cm. The relative accuracy, defined as the ratio of RMS and tidal range, is between 2.4% and 10.0% for all stations.Comparing the standard analysis method and the extended analysis method, the results based on theextended analysis method agree better with the independent tide gauge records for the stations with a high tidal range. For the station with the highest tidal range (772 cm), the RMS is reduced by 47% when using the extended analysis method. Furthermore, the results also indicate that the standard analysis method, assuming a static sea level, can be used for stations with a tidal range of up to about 270 cm, without performing significantly worse than the extended analysis method.Tidal amplitudes and phases are derived by harmonic analysis of the sea level records. Again, a high level of agreement is observed between the tide gauge and the GPS-derived results. Comparing the GPS-derived results, the results based on the extended analysis method show a higher degree of agreement with the traditional tide gauge results for stations with larger tidal ranges. Spectral analysis of the residuals after the harmonic analysis reveals remaining signal power at multiples of the draconitic day. This indicates that the observed SNR data are to some level disturbed by additional multipath signals, in particular for GPS stations that are located in harbors.
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| 45. |
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| 46. |
- Löfgren, Johan, 1983, et al.
(författare)
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Three months of local sea level derived from reflected GNSS signals
- 2011
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 46:RS0C05
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Tidskriftsartikel (refereegranskat)abstract
- By receiving Global Navigation Satellite System (GNSS) signals that are reflected off the sea surface, together with directly received GNSS signals (using standard geodetic‐type receivers), it is possible to monitor the sea level using regular single difference geodetic processing. We show results from our analysis of three months of data from the GNSS‐based tide gauge at the Onsala Space Observatory (OSO) on the west coast of Sweden. The GNSS-derived time series of local sea level is compared with independent data from two stilling well gauges at Ringhals and Gothenburg about 18 km south and 33 km north of OSO, respectively. A high degree of agreement is found in the time domain, with correlation coefficients of up to 0.96. The root‐mean‐square differences between the GNSS‐derived sea level and the stilling well gauge observations are 5.9 cm and 5.5 cm, which is lower than for the stilling well gauges together (6.1 cm). A frequency domain comparison reveals high coherence of the data sets up to 6 cycles per day, which corresponds well to the propagation of gravity waves in the shallow waters at the Kattegat coast. Amplitudes and phases of some major tides were determined by a tidal harmonic analysis and compared to model predictions. From the GNSS‐based tide gauge results we find significant ocean tidal signals at fortnightly, diurnal, semi‐diurnal, and quarter‐diurnal periods. As an example, the amplitudes of the semi‐diurnal M2 and the diurnal O1 tide are determined with 1σ uncertainties of 11 mm and 12 mm, respectively. The comparison to model calculations shows that global ocean tide models have limited accuracy in the Kattegat area.
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| 47. |
- Mantovani, Matteo, 1974, et al.
(författare)
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DInSAR investigation in the Pärvie endglacial fault region, Lapland, Sweden
- 2013
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 34:23, s. 8491-8502
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Tidskriftsartikel (refereegranskat)abstract
- Northern Fennoscandia bears witness to the Pleistocene glaciation in the form of a seriesof large faults that have been shown to have ruptured immediately after the retreat ofthe ice sheet, about 9500 years ago. The largest one, known as the Pärvie fault, consistsof a 155 km long linear series of fault scarps forming north–northeast-trending, thatstretch west of Kiruna, Lapland. End-glacial intra-plate faults of this extent are veryrare in the continental crust and the Pärvie system represents one of the major faultzone structures of this type in the world. Seismological evidence shows that there isstill noticeable seismic activity, roughly one event of magnitude 2 per year that can beattributed to the fault. Nevertheless assessing its state of activity is a difficult task dueto the extent and remoteness of the area. This study is aimed at the determination ofcrustal motion around the Pärvie fault zone using the differential inter-ferometric syntheticaperture radar (DInSAR) technique, based on images acquired with the EuropeanSpace Agency (ESA) satellites European Remote Sensing (ERS) 1, ERS-2, and theEnvironmental Satellite (ENVISAT). We present results achieved in terms of deformationof the crystalline bedrock along different sectors of the fault where high levels ofcoherence were obtained, even from image pairs several years apart. This finding doesnot exclude deformation in other segments, as observing conditions are not always asfavourable in terms of data availability.
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| 48. |
- Mantovani, Matteo, 1974, et al.
(författare)
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Observation of Crustal Deformation around the Pärvie Postglacial Fault, Lapland, Sweden, using InSAR techniques
- 2012
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Ingår i: European Geosciences Union General Assembly 2012, 22-27 April, Vienna, Austria.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Pärvie postglacial fault is a 155 km long fault that probably snapped in one single and anomalously steepreverse-slip event at the end of the Pleistocene glaciation about 9,500 ybp. Still today the seismicity, limitedto roughly one magnitude-3.5 event per 15 years, one M=2 event per year, is anomalous and events have beenattributed to the fault system by seismologists. In this project we try to find signatures of deformation usingdifferent interferometric Radar Remote Sensing techniques. A stack of ERS and ENVISAT acquisitions straddlingover 15 years has been analysed with multi-baseline interferometric stacking (MB) and with the Short Baseline(SBAS) method. Also Persistent Scatterer methods have been attempted, but with less success owing to the lackof strong and sharply confined reflectors. In our findings we notice correlation between mm-sized displacementsin outlined zones near the fault; they appear to correlate with the variations of seismicity that seismologists of theSwedish National Seismic Network have determined. In addition, rockfalls and slumps in areas of typically 1-3 kmdiameter could be found. The results of SBAS and MB techniques show comparable signatures of deformation.Our results may bracket the range of the ratio of "aseismic" to seismoc slip in this area. The fault scarp itself is notvisible in the deformation patterns. Thus we expect rather low values for this ratio.
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| 49. |
- Milne, G.A., et al.
(författare)
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Continuous GPS measurements of postglacial adjustment in Fennoscandia: 2. Modeling results
- 2004
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 109:B2
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Tidskriftsartikel (refereegranskat)abstract
- [1] Data collected under the auspices of the BIFROST GPS project yield a geographically dense suite of estimates of present-day, three-dimensional (3-D) crustal deformation rates in Fennoscandia [Johansson et al., 2002]. A preliminary forward analysis of these estimates [Milne et al., 2001] has indicated that models of ongoing glacial isostatic adjustment (GIA) in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3-D velocity field. In this study we revisit our previous GIA analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the BIFROST rate estimates. To establish insight into the physics of the GIA response in the region, we begin by decomposing a forward prediction into the three contributions associated with the ice, ocean, and rotational forcings. From this analysis we demonstrate that recent advances in postglacial sea level theory, in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin, involve peak signals that are larger than the observational uncertainties in the BIFROST network. The forward analysis is completed by presenting predictions for a pair of Fennoscandian ice histories and an extensive suite of viscoelastic Earth models. The former indicates that the BIFROST data set provides a powerful discriminant of such histories. The latter yields bounds on the ( assumed constant) upper and lower mantle viscosity (nu(UM), nu(LM)); specifically, we derive a 95% confidence interval of 5 x 10(20) less than or equal to nu(UM) less than or equal to 10(21) Pa s and 5 x 10(21) less than or equal to nu(LM) less than or equal to 5 x 10(22) Pa s, with some preference for (elastic) lithospheric thickness in excess of 100 km. The main goal of the ( Bayesian) inverse analysis is to estimate the radial resolving power of the BIFROST GPS data as a function of depth in the mantle. Assuming a reasonably accurate ice history, we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle. We conclude that the BIFROST data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer. However, these data provide little constraint on viscosity in the bottom half of the mantle. Finally, elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity.
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| 50. |
- Milne, Glenn A., et al.
(författare)
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Space-Geodetic Constraints on Glacial Isostatic Adjustment in Fennoscandia
- 2001
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Ingår i: Science. - 0036-8075 .- 1095-9203. ; 291:23 March 2001, s. 2381-2385
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisÞes independent geologic constraints and bounds both the average viscosity in the upper mantle (5 x 10^20 to 1 x 10^21 pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than ~1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field.
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