Calibration of the C021 Superconducting Gravimeter in Membach (Belgium) Using 47 Days of Absolute Gravity Measurements

1997 ◽  
pp. 212-219 ◽  
Author(s):  
O. Francis
Keyword(s):  
Superconducting Gravimeter ◽  
Absolute Gravity ◽  
Gravity Measurements

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 Observed secular gravity trend at Onsala station with the FG5 gravimeter from Hannover

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
L. Timmen ◽  
A. Engfeldt ◽  
H.-G. Scherneck
Keyword(s):  
Superconducting Gravimeter ◽  
Absolute Gravity ◽  
Absolute Gravimeter ◽  
Land Uplift ◽  
Isostatic Adjustment ◽  
Sea Bottom ◽  
Onsala Space Observatory ◽  
Mass Load ◽  
Gravity Effects ◽  
Gravity Measurements

AbstractAnnual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observatory by the Institute of Geodesy of the Leibniz Universität Hannover from 2003 to 2011 and have been continued with the upgraded meter FG5X in 2014. Lantmäteriet, Gävle, with their FG5 absolute gravimeter have visited Onsala since 2007. Because small systematic errors may be inherent in each absolute gravimeter, their measuring level and a resulting bias (offset) between the instruments must be controlled over time by means of inter-comparison. From 2007 to 2014, 8 direct comparisons took place well distributed over the time span. A complete re-processing of the absolute gravity observations with the Hannover instrument has been conducted to improve the reduction of unwanted gravity effects. A new tidal model is based on continuous time series recorded with the GWR superconducting gravimeter at Onsala since 2009. The loading effect of the Kattegat is described with a varying sea bottom pressure (water and air mass load) and has been validated with the continuous gravity measurements. For the land uplift,which is a result of the still ongoing glacial isostatic adjustment in Fennoscandia, a secular gravity trend of −0.22 μGal/yr was obtained with a standard deviation of 0.17 μGal/yr. That indicates a slight uplift but is still not significantly different from zero.

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>

scholarly journals On the calibration of a superconducting gravimeter using absolute gravity measurements

1991 ◽  
Vol 106 (2) ◽  
pp. 491-497 ◽  
Author(s):  
J. Hinderer ◽  
N. Florsch ◽  
J. Mäkinen ◽  
H. Legros ◽  
J. E. Faller
Keyword(s):  
Superconducting Gravimeter ◽  
Absolute Gravity ◽  
Gravity Measurements

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.

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