scholarly journals Gravity reference at the Argentinean–German Geodetic Observatory (AGGO) by co-location of superconducting and absolute gravity measurements

2020 ◽  
Vol 94 (9) ◽  
Author(s):  
Ezequiel D. Antokoletz ◽  
Hartmut Wziontek ◽  
Claudia N. Tocho ◽  
Reinhard Falk
Keyword(s):  
Gravity Data ◽  
Total Error ◽  
International Comparisons ◽  
Superconducting Gravimeter ◽  
Calibration Factor ◽  
Absolute Gravity ◽  
Absolute Level ◽  
Gravity Measurements ◽  
Instrumental Drift

AbstractThe Argentinean–German Geodetic Observatory (AGGO) is a fundamental geodetic observatory located close to the city of La Plata, Argentina. Two high-precision gravity meters are installed at AGGO: the superconducting gravimeter SG038, which is in operation since December 2015, and the absolute gravimeter FG5-227, which has provided absolute gravity measurements since January 2018. By co-location of gravity observations from both meters between January 2018 and March 2019, calibration factor and instrumental drift of the SG038 were determined. The calibration factor of the SG038 was estimated by different strategies: from tidal models, dedicated absolute gravity measurements over several days and a joint approach (including the determination of the instrumental drift) using all available absolute gravity data. The final calibration factor differs from the determination at the previous station, the transportable integrated geodetic observatory, in Concepcion, Chile, by only 0.7‰, which does not imply a significant change. From the combined approach also the mean absolute level of the SG was determined, allowing to predict absolute gravity values from the SG at any time based on a repeatability of $$12\,\hbox {nm}/\hbox {s}^{2}$$ 12 nm / s 2 for the FG5-227 at AGGO. Such a continuous gravity reference function provides the basis for a comparison site for absolute gravimeters in the frame of the international gravity reference frame for South America and the Caribbean. However, it requires the assessment of the total error budget of the FG5-227, including the link to the international comparisons, which will be subject of future efforts.

scholarly journals Twelve Years of High Frequency Absolute Gravity Measurements at the UK’s Space Geodesy Facility: Systematic Signals and Comparison with SLR Heights

2021 ◽  
Author(s):  
Victoria Anne Smith ◽  
Graham Appleby ◽  
Marek Ziebart ◽  
Jose Rodriguez
Keyword(s):  
Time Series ◽  
Gravity Data ◽  
International Comparisons ◽  
Vertical Motion ◽  
Space Geodesy ◽  
Global Navigation Satellite Systems ◽  
Absolute Gravity ◽  
Soil Parameters ◽  
Satellite Systems ◽  
Gravity Measurements

AbstractAbsolute gravity measurements taken on a near-weekly basis at a single location is a rarity. Twelve years of data at the UK’s Space Geodesy Facility (SGF) provides evidence to show that the application of results from international comparisons of absolute gravimeters should be applied to data and are critical to the interpretation of theSGF gravity time series of data from 2007 to 2019. Though residual biases in the data are seen. The SGF time series comprises near weekly data, with exceptions for manufacturer services and participation in international instrument comparisons. Each data set comprises hourly data taken over 1 day, with between 100 and 200 drops per hour. Environmental modelling indicates that the annual groundwater variation at SGFof some 2 m influences the gravity data by 3.1 μGal, based upon some measured and estimated soil parameters. The soil parameters were also used in the calculation of the effect of an additional telescope dome, built above the gravity laboratory, and have been shown to be realistic. Sited in close proximity to the long-established satellite laser ranging (SLR) system and the global navigation satellite systems (GNSS) the absolute gravimetry (AG) measurements provide a complimentary geodetic technique, which is non space-based. The SLR-derived height time series provides an independent measurement of vertical motion at the site which may be used to assess the AG results, which are impacted by ground motion as well as mass changes above and below the instruments.

scholarly journals Measuring gravity changes for decades

2020 ◽  
Author(s):  
Michel Van Camp ◽  
Olivier de Viron ◽  
Bruno Meurers ◽  
Olivier Francis
Keyword(s):  
Gravity Data ◽  
Superconducting Gravimeter ◽  
Rate Of Change ◽  
Earth Tides ◽  
Convective Precipitation ◽  
Absolute Gravity ◽  
Tectonic Deformation ◽  
Time Frequency ◽  
Gravity Measurements ◽  
The Impact

<p>Being sensitive to any phenomena associated with mass transfer, terrestrial gravimetry allows the monitoring of many phenomena at the 10<sup>-10</sup> g level (1 nm/s²) such as Earth tides, groundwater content, tectonic deformation, or volcanic activity. This sensitivity is richness, but also a source of problems because data interpretation requires separating the signatures from the different sources, including possible measurement artefacts associated with high precision. Separating the signal from a given source requires a thorough knowledge of both the instrument and the phenomena.</p><p>At the Membach geophysical laboratory, Belgium, the same superconducting gravimeter has monitored gravity continuously for more than 24 years. Together with 300 repeated absolute gravity measurements and environmental monitoring, this has allowed us to reach an unprecedented metrological knowledge of the instrument and of its sensitivity to hydrological and geophysical signals.</p><p>Separation is possible whenever the phenomena exhibit distinct time/frequency signatures, such as (pseudo)periodic phenomena or long-term processes, so that the signatures from other sources average out by stacking. For example, when performing repeated gravity measurements to evidence slow tectonic deformation, the easiest way to mitigate hydrological effects is to accumulate measurements for many years, at the same epoch of the year: the impact of seasonal variations is then minimized, and the interannual variations cancel out. Using 10 repeated absolute gravity campaigns at the same epoch of the year, we showed that the gravity rate of change uncertainty reaches on average 3–4 nm/s²/yr. Concurrently, using superconducting gravimeter time series longer than 10 years, we also investigated the time variations of tidal parameters.</p><p>It is also possible to separate phenomena by observing them by both gravity and some other techniques, with a different transfer function. By using 11 year-long times series from the gravimeter and soil moisture probes, and by stacking the observations, we measured directly the groundwater mass loss by evapotranspiration in the forest above the laboratory of Membach. Always with a precision better than 1 nm/s² (<=> 2.5 mm of water), we also monitored ground partial saturation dynamics and combining the gravity data with a weather radar allowed measuring convective precipitation at a scale of up to 1 km².</p><p>Extracting and interpreting those elusive signals could only by achieved throughout multi-instrumentation, multi-disciplinary collaborative studies, and 25 years of hard work.</p>

Comparison between a six-year (2015-2020) continuous time series from an iGrav superconducting gravimeter and absolute gravity data at Mt. Etna volcano (Italy).

2021 ◽  
Author(s):  
Filippo Greco ◽  
Daniele Carbone ◽  
Alfio Alex Messina ◽  
Danilo Contrafatto
Keyword(s):  
Time Series ◽  
Continuous Time ◽  
Gravity Data ◽  
Total Error ◽  
Superconducting Gravimeter ◽  
Repeated Measurements ◽  
Absolute Gravity ◽  
Data Sets ◽  
Gravity Changes ◽  
Mt Etna

<p>Since September 2014, iGrav#016 superconducting gravimeter (SG; by GWR) has recorded continuously at the Serra La Nave Astrophysical Observatory (SLN; 1730 m elevation; ~6.5 km from the Etna’s summit craters; Italy).</p><p>Here we present results of a comparison between a six-year (2015-2020) time series from iGrav#16 and absolute gravity data collected through the Microg LaCoste FG5#238 absolute gravimeter (AG), in the framework of repeated measurements that were performed at the same installation site of the SG. Both AG and SG records have been corrected for the local tides, local atmospheric pressure and for the polar motion effect.</p><p>The comparison allows to estimate the long-term drift of the SG, defined as the total SG trend minus the observed trend in AG measurements, which is of the order of 9 microGal/year. Once the drift effect is removed,  there is a remarkably good fit between the two data sets. The differences between absolute gravity changes and corresponding relative data in the continuous time series from the SG are within 1-2 microGal (the total error on AG measurements at this station is typically +/- 3 microGal).</p><p>After being corrected for the effect of instrumental drift, the time series from the SG reveals gravity changes that are due to hydrological and volcanological effects.</p><p>Our study shows how the combination of repeated AG measurements and continuous gravity observations through SGs can be used to obtain a fuller and more accurate picture of the temporal characteristics of the studied processes.</p>

scholarly journals Calibration of the Latest Generation Superconducting Gravimeter iGrav-043 Using the Observatory Superconducting Gravimeter OSG-CT040 and the Comparisons of Their Characteristics at the Walferdange Underground Laboratory for Geodynamics, Luxembourg

2022 ◽  
Author(s):  
Basem Elsaka ◽  
Olivier Francis ◽  
Jürgen Kusche
Keyword(s):  
Gravity Data ◽  
Electrical Power ◽  
Superconducting Gravimeter ◽  
Calibration Factor ◽  
Underground Laboratory ◽  
Linear Behavior ◽  
Exponential Decrease ◽  
The University ◽  
Instrumental Drift

AbstractIn December 2019, the latest generation transportable superconducting gravimeter (SG) iGrav-043 purchased by the University of Bonn was installed in the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. In this paper, we estimate the calibration factor of the iGrav-043, which is essential for long-term gravity monitoring. We used simultaneously collected gravity data from the un-calibrated iGrav-043 and the calibrated Observatory superconducting gravimeter OSG-CT040 that operates continuously at WULG since 2002. The tidal analysis provides a simple way to transfer the calibration factor of one SG to the other. We then assess and compare tidal analyses, instrumental drifts and high frequency noises. After 20 years of continuous operation, the instrumental drift of the OSG-CT040 is almost zero. From 533 days of joint operation, we found that the instrumental drift of iGrav-043 exhibits a composite behavior: just after the setup and for two months a fast exponential decrease of 171 nm s−2, then a linear with a rate of 66 nm s−2 ± 10 nm s−2 per year. We suggest that a period of 3 months is sufficient for calibrating the iGrav. Accidental electrical power cuts triggered slight differences in the reaction and recovery of the OSG-CT040 and iGrav-043. However, it has been found that the long-term linear behavior of the drift was not affected.

scholarly journals The first tidal analysis based on the CG-5 Autograv gravity measurements at Modra station

2013 ◽  
Vol 43 (1) ◽  
pp. 59-72 ◽  
Author(s):  
Michal Mikolaj ◽  
Branislav Hábel
Keyword(s):  
Maximum Amplitude ◽  
Superconducting Gravimeter ◽  
Absolute Gravity ◽  
Ocean Tides ◽  
Tidal Analysis ◽  
Tidal Waves ◽  
Gravity Measurements ◽  
Relative Gravity ◽  
Factor Difference ◽  
Instrumental Drift

Abstract We present the tidal parameters estimated for the absolute gravity site in Modra (Slovakia). This is the first tidal analysis based on gravity measurements for this location. Relative gravity variations observed by Scintrex CG-5 Autograv gravimeter were used for the tidal analysis. We observed large and non-linear instrumental drift which cannot be effectively eliminated by polynomial approximation. Drift was eliminated by a filtering. New set of tidal parameters was estimated and analyzed with the focus on diurnal and semi-diurnal tidal waves. Time and frequency domain comparison between new parameters and those obtained from the superconducting gravimeter located in Vienna was performed. A maximum amplitude factor difference of 0.2% was found between main tidal waves corrected for ocean tides and non-hydrostatic body tide model. New estimated tidal parameters can serve for the correction of local relative gravity measurements

scholarly journals Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

2021 ◽  
Vol 95 (2) ◽  
Author(s):  
Mirjam Bilker-Koivula ◽  
Jaakko Mäkinen ◽  
Hannu Ruotsalainen ◽  
Jyri Näränen ◽  
Timo Saari
Keyword(s):  
Gravity Data ◽  
Gravity Change ◽  
Global Navigation Satellite Systems ◽  
Absolute Gravity ◽  
Data Sets ◽  
Postglacial Rebound ◽  
Land Uplift ◽  
Satellite Systems ◽  
Gravity Measurements ◽  
Global Navigation Satellite

AbstractPostglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

An integrated approach for understanding long-term volcano dynamics based on absolute gravity and GNSS measurements

2020 ◽  
Author(s):  
Alessandro Bonforte ◽  
Filippo Greco ◽  
Daniele Carbone
Keyword(s):  
Gravity Data ◽  
General Pattern ◽  
Integrated Approach ◽  
Absolute Gravity ◽  
Gravity Measurements ◽  
Mt Etna ◽  
Elevation Changes ◽  
Spatio Temporal ◽  
Gnss Measurements ◽  
Relative Measurements

<p>Here we present the results of repeated Absolute Gravity and GNSS measurements, collected at Mt. Etna (Italy) between 2009 and 2018. We aim at investigating the capabilities of this integrated approach for understanding the dynamics of magmatic sources over time-scales of months to years. The absolute gravity and GNSS campaign measurements were repeated roughly once a year; in order to improve the time resolution of gravity data, in some stations we performed, besides absolute gravity measurements, also relative measurements at intervals shorter than 1 year.</p><p>After being corrected for the effect of elevation changes, gravity data reveal an increase/decrease cycle, well spatio-temporal correlated with a general pattern of uplift/subsidence, during a period of intense lava fountains from the summit craters.</p><p>Our results provide insight into the processes that controlled the transfer of the magma from deeper to shallower levels of the plumbing system of Mt. Etna volcano, in periods preceding/accompanying the eruptive activity during 2009–2018.</p><p>Specifically, we propose that coupled changes in height-corrected gravity and elevation might be induced either by the magma storage/withdrawal below the volcanic pile, or by fluids pressurization/depressurization, or by a combination of both processes.</p><p>The application of the proposed approach could led to an improved capability to identify processes heralding eruptions.</p>

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