| 1. |
- 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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| 2. |
- Scherneck, Hans-Georg, 1951, et al.
(författare)
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Fennoscandian strain rates from BIFROST GPS: A gravitating, thick-plate approach
- 2010
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 50:1, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this investigation is to develop a method for the analysis of crustal strain determined bystation networks that continuously measurements of Global Navigation Satellite Systems (GNSS). Themajor new ingredient is that we require a simultaneous minimum of the observation error and theelastic and potential energy implied by the deformation.The observations that we analyse come from eight years worth of daily solutions from continuousBIFROST GPS measurements in the permanent networks of the Nordic countries and their neighbours.Reducing the observations with best fitting predictions for the effects of glacial isostatic adjustment (GIA)we find strain rates of maximum 5 nano/yr in the interior of the rebound area predominantly as arealstrain. The largest strain rates are found in the Finnmarken area, where however the GNSS networkdensity is much lower than in the central and southern parts.The thick-plate adjustment furnishes a simultaneous treatment of 3-D displacements and the ensuingelastic and potential energy due to the deformation. We find that the strain generated by flexure due toGIA is important. The extensional regime seen at the surface turns over into a compressive style alreadyat moderated depth, some 50 km.
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| 3. |
- 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. ; , s. 1-52, 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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| 4. |
- Scherneck, Hans-Georg, 1951, et al.
(författare)
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Using a Superconducting Gravimeter in Support of Absolute Gravity Campaigning — A Feasibility Study
- 2019
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Ingår i: Geophysica. - 0367-4231 .- 2324-0741. ; 54:1, s. 117-135
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Tidskriftsartikel (refereegranskat)abstract
- Preparing for joint analysis of absolute gravity (AG) campaigns, this report investigates whether a stationary superconducting gravimeter (SCG) can provide a long-term stable measurement of sitedependent perturbations that help in reduction to the local value of little-g and its secular rate of change. The crucial element concerns the discrimination of instrumental drift components from trends of physical origin, where biasses in the inferred long-term drift rate may offset the rate that the reduced AG campaigns deliver. Thus, the main objective is to include a set of gravity models and proxy series as complete as possible in the SCG analysis. Findings indicate consistency for dg/dt in the drift model at the 0.5 nm/s2/yr level using observations at Onsala Space Observatory from 2009 to 2017. In pursuit of the overriding objective to improve the accuracy of secular rates of gravity owed to Glacial Isostatic Adjustment, our approach may even put numbers on a range of long-term changes due to atmosphere, hydrology, and non-tidal ocean loading, namely the rate biasses reported here.
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| 5. |
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| 6. |
- 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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| 7. |
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| 8. |
- 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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| 9. |
- 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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| 10. |
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