| 1. |
- Timmen, Ludger, et al.
(författare)
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Observing Fennoscandian Gravity Change by Absolute Gravimetry
- 2006
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Ingår i: International Association of Geodesy Symposia, Vol. 131, Geodetic Deformation Monitoring: From Geophysical to Engineering Roles. ; , s. 193-199
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Nordic countries Norway, Sweden, Denmark and Finland are a key study region for the research of glacial isostasy, and, in addition, it offers a unique opportunity for validating and testing the results of the GRACE experiment. Over a period of five years, the expected life time of GRACE, a temporal geoid variation of 3.0 mm is expected in the centre of the Fennoscandian land uplift area, corresponding to a gravity change of about 100 nm/s2. This is expected to be within the detection capabilities of GRACE. With terrestrial absolute gravimetry, the gravity change due to the land uplift can be observed with an accuracy of ±10 to 20 nm/s2 for a 5-year period. Thus, the terrestrial insitu observations (ground-truth) may be used to validate and test the GRACE results.Since 2003, absolute gravity measurements have been performed in Fennoscandia at about 30 stations covering Norway, Sweden, Finland and Denmark. Four groups with FG5 absolute gravimeters (BKG, FGI, IfE, UMB) are engaged to survey the uplift network annually by a mutually controlled procedure. Nearly all absolute stations are colocated with permanent GPS stations. From the 2003 and 2004 comparisons between the instruments, an overall accuracy of ±30 nm/s2 is indicated for a single absolute gravimeter and a single station determination. This is in full agreement with the project goal.
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| 2. |
- Engfeldt, Andreas, et al.
(författare)
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RG 2000 – the New Gravity Reference Frame of Sweden
- 2019
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Ingår i: Geophysica. - : Geophysical Society of Finland. - 0367-4231 .- 2324-0741. ; 54:1, s. 69-92
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Tidskriftsartikel (refereegranskat)abstract
- The increased need for improved geoid models for Global Navigation Satellite Systems (GNSS) height determination calls for additional gravity observations and quality assurance of existing data. In this perspective, a modern gravity system and the renovation of an already existing high order gravity network is considered as a moderate strategic investment which provides a firm foundation for further activities. Here the new gravity reference frame RG 2000 for Sweden is presented. RG 2000 is realized by absolute gravity observations at 109 stations. The absolute points are connected via old and new relative gravity observations, including another 216 points. Points and observations have been chosen so that good overlap with the older Swedish reference frames, RG 62 and RG 82, is achieved, allowing to evaluate the older frames and transformations between them. RG 2000 is based on a zero permanent tide system with epoch 2000.
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| 3. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Preliminary Results in the Baltic Sea
- 2020
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 12:22
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Tidskriftsartikel (refereegranskat)abstract
- Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to the geometric network of a country by operating permanent GNSS receivers next to the tide gauge. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans. First results from applying this technique at selected tide gauges at the Baltic coasts are promising but also exhibit some problems related to the new technique. The paper presents the concept of using the new observation type in an integrated sea level observing system and provides some early results for SAR positioning in the Baltic sea area.
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| 4. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Results in the Baltic Sea
- 2022
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Konferensbidrag (refereegranskat)abstract
- Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to permanent GNSS receivers next to the tide gauge in order to systematically observe vertical land motion. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans.The paper presents the results of a project, which was conducted in the years 2019 to 2021 in the frame of ESA´s Baltic+ initiative. Within this project a test network of electronic corner reflectors (ECR) as targets for Sentinel-1 was realized in the Baltic Sea area. The ECR locations were either co-located with tide gauges or with permanent GNSS stations in order to observe systematically the ellipsoidal heights of the tide gauges and possibly also any vertical land motion at the stations. Data for the year 2020 were collected at 10 stations in Estonia, Finland, Poland and Sweden and jointly analyzed with GNSS data, tide gauge records and regional geoid height estimates. The obtained results are promising, but also exhibit some problems related to the ECR´s and their performance. At co-located GNSS stations the estimated ellipsoidal heights agree in a range between about 2 and 50 cm between both observation systems. From the results it could be identified that most likely variable systematic electronic instrument delays of the ECR´s are the main reason for these differences and that each instrument needs to be calibrated individually. Nevertheless, the project provides a valuable data set, which offers the possibility to enhance methods and procedures in order to develop the geodetic SAR positioning technique towards operability. All data and reports are accessible at the following web site: https://www.asg.ed.tum.de/iapg/baltic/
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| 5. |
- Gruber, Thomas, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Results in the Baltic Sea Test Network
- 2022
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Ingår i: Remote Sensing. - : MDPI. - 2072-4292. ; 14:14
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Tidskriftsartikel (refereegranskat)abstract
- Coastal sea level is observed at tide gauge stations, which usually also serve as height reference stations for national networks. One of the main issues with using tide gauge data for sea level research is that only a few stations are connected to permanent GNSS stations needed to correct for vertical land motion. As a new observation technique, absolute positioning by SAR using off the shelf active radar transponders can be installed instead. SAR data for the year 2020 are collected at 12 stations in the Baltic Sea area, which are co-located to tide gauges or permanent GNSS stations. From the SAR data, 3D coordinates are estimated and jointly analyzed with GNSS data, tide gauge records and regional geoid height estimates. The obtained results are promising but also exhibit some problems related to the electronic transponders and their performance. At co-located GNSS stations, the estimated ellipsoidal heights agree in a range between about 2 and 50 cm for both observation systems. From the results, it can be identified that, most likely, variable systematic electronic instrument delays are the main reason, and that each transponder instrument needs to be calibrated individually. Nevertheless, the project provides a valuable data set, which offers the possibility of enhancing methods and procedures in order to develop a geodetic SAR positioning technique towards operability.
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| 6. |
- Scherneck, Hans-Georg, 1951, et al.
(författare)
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Superconducting gravimeter and seismometer shedding light on FG5’s offsets, trends and noise: what observations at Onsala Space Observatory can tell us
- 2020
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Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 94:9
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Tidskriftsartikel (refereegranskat)abstract
- Ten-year worth of absolute gravity (AG) campaigns at Onsala Space Observatory (OSO), Sweden, are simultaneously reduced using synchronous data from a superconducting gravimeter (SG). In this multi-campaign adjustment, the a priori models commonly applied for each setup in AG-alone experiments are sidestepped in favour of SG records and a model to estimate its drift. We obtain a residual (hourly samples) at the 5 nm/s2 RMS level, reducing the SG data with a range of ancillary data for the site’s exposure to ocean and atmospheric loading, and hydrology effects. The target quantity in AG projects in the Baltic Shield area is the secular change of gravity dominated by glacial isostatic adjustment with land uplift as its major part. Investigating into the details of the associated processes using AG requires a long-term stable reference, which is the aim of international comparison campaigns of FG5 instruments. Two of these have been campaigning at OSO since 2009 when the SG had been installed. In the simultaneous inversion of all sixteen campaigns, we identify weaknesses of AG observations, like varying systematic offsets over time, excess microseismic sensitivity, trends in the AG data and side effects on the SG’s scale factor when campaigns are evaluated one by one. The simultaneous adjustment afforded us an SG scale factor very near the result from a campaign with a prototype quantum gravimeter.Whence, we propose that single-campaign results may be biased and conjectures into their variation, let alone its causes misleading. The OSO site appears to present manageable problems as far as environmental influences are concerned. Our findings advocate the use of AG instruments and procedures that are more long-term stable (reference realization), more short-term stable too (setup drifts), less service craving and more resilient to microseismic noise.
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| 7. |
- Strandberg, Emelie, 1986-, et al.
(författare)
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Influence of combined resistance training and healthy diet on muscle mass in healthy elderly women : a randomized controlled trial
- 2015
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 119:8, s. 918-925
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Tidskriftsartikel (refereegranskat)abstract
- The delivery of efficient nonpharmacological treatment to prevent the loss of muscle mass in older adults is a major challenge, and information on the combined effects of training and diet is particularly important. Here we aimed to evaluate the effects of 24 wk of resistance training combined with a healthy dietary approach (n-6/n-3 ratio < 2) in a population of healthy and physically active older women (65-70 years). The three-armed randomized controlled trial included a resistance training + healthy diet group (RT-HD), a resistance training group (RT), and controls (CON). All subjects included in the study were physically active and had low levels of serum inflammatory markers. In accordance with the dietary goals, the n-6/n-3 ratio dietary intake significantly decreased only in RT-HD by 42%. An increase in 1 repetition maximum in leg extension occurred in RT (+20.4%) and RT-HD (+20.8%), but not in CON. Interestingly, leg lean mass significantly increased only in RT-HD (+1.8%). While there were no changes in serum C-reactive protein and IL-6 levels, a significant decrease in serum level of the pro-inflammatory precursor arachidonic acid (-5.3 +/- 9.4%) together with an increase in serum n-3 docosahexaenoic acid (+8.3%) occurred only in RT-HD. Altogether, this study demonstrates that the effects of resistance training on muscle mass in healthy older adults can be optimized by the adoption of a healthy diet.
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| 8. |
- Timmen, Ludger, et al.
(författare)
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Observed secular gravity trend at Onsala station with the FG5 gravimeter from Hannover.
- 2015
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Ingår i: Journal of Geodetic Science. - : Walter de Gruyter GmbH. - 2081-9943. ; 5:1, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- Annual absolute gravity measurements with aFG5 instrument were performed in Onsala Space Observatoryby the Institute of Geodesy of the Leibniz UniversitätHannover from 2003 to 2011 and have been continued withthe upgraded meter FG5X in 2014. Lantmäteriet, Gävle,with their FG5 absolute gravimeter have visited Onsalasince 2007. Because small systematic errors may be inherentin each absolute gravimeter, their measuring level anda resulting bias (offset) between the instruments must becontrolled over time by means of inter-comparison. From2007 to 2014, 8 direct comparisons took place well distributedover the time span. A complete re-processing ofthe absolute gravity observations with the Hannover instrumenthas been conducted to improve the reduction ofunwanted gravity effects. A new tidal model is based oncontinuous time series recorded with the GWR superconductinggravimeter at Onsala since 2009. The loading effectof the Kattegat is described with a varying sea bottompressure (water and air mass load) and has been validated with the continuous gravity measurements. For theland uplift,which is a result of the still ongoing glacial isostaticadjustment in Fennoscandia, a secular gravity trendof −0.22 μGal/yr was obtained with a standard deviationof 0.17 μGal/yr. That indicates a slight uplift but is still notsignificantly different from zero.
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