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Results of absolute measurements at point A.090 during ICAG-2001 (; Table 6) and ICAG-97 (•) for each gravimeter. Solid line: unweighted mean value of ICAG-97 (980 925 707.8 ± 2.8) µGal; dashed line: weighted mean value with some omitted data of absolute measurements of ICAG-2001 (980 925 701.2 ± 5.5) µGal.
Source publication
The Sixth International Comparison of Absolute Gravimeters was held from 5 June to 28 August 2001 at the Bureau International des Poids et Mesures (BIPM), Sèvres. Seventeen absolute gravimeters were used to make measurements at five sites of the BIPM gravity network. The vertical gravity gradients at the sites and the ties between them were also me...
Contexts in source publication
Context 1
... results of the combined adjustment of the relative and absolute data of ICAG-2001 with some data omitted (column 14 of Table 6), are shown in Figure 6 together with the results of the absolute measurements during ICAG-97. The weighted mean of the absolute measurements during ICAG-2001 is (980 925 701.2 ± 5.5) µGal (Table ...
Context 2
... value at A.090 obtained from thirteen absolute gravimeters during ICAG-2001 (Table 6a and Figure 6) is 6.6 µGal lower than the value obtained from fifteen gravimeters during ICAG-97. Eight of these gravimeters participated in both ICAG-97 and ICAG-2001. The results obtained in the two compar- isons lie within 2 µGal (i.e. negligible difference) for two gravimeters; the difference 2001 -1997 is positive for two gravimeters and negative for the other ...
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Citations
... Germany. The different CRVs solutions are presented by [23] for ECAG2003, [24] for ECAG2007, and by [25] for the others. Shortly after the comparison in 2003, an instrumental instability was detected and eliminated: the input beam fiber was only poorly attached to the interferometer base and started to loosen. ...
In 2004, first absolute gravity (AG) measurements were performed on the top of Mt. Zugspitze (2 sites) and at the foot (1 site) and top (1 site) of Mt. Wank. Mt. Wank (summit height 1780 m) and Mt. Zugspitze (2960 m) are about 15 km apart from each other and belong geologically to different parts of the Northern Limestone Alps. Bridging a time span of 15 years, the deduced gravity variations for Zugspitze are in the order of 0.30 μm/s² with a standard uncertainty of 0.04 μm/s². The Wank stations (foot and top) show no significant gravity variation. The vertical stability of Wank summit is also confirmed by results of continuous GNSS recordings. Because an Alpine mountain uplift of 1 or 2 mm/yr cannot explain the obtained gravity decline at Zugspitze, the dominating geophysical contributions are assumed to be due to the diminishing glaciers in the vicinity. The modelled gravity trend caused by glacier retreat between epochs 1999 and 2018 amounts to 0.012 μm/s²/yr at both Zugspitze AG sites. This explains more than half of the observed gravity decrease. Long-term variations on inter-annual and climate-relevant decadal scale will be investigated in the future using as supplement superconducting gravimetry (installed in 2019) and GNSS equipment (since 2018).
... Nowadays the primary location for comparisons within Europe, and arguably the world, is the Walferdange Underground Laboratory of Geodesy in the grand duchy of Luxembourg, which first hosted the ICAG in 2013, but was first used as a comparison site in 2003, for a European Comparison of Absolute Gravimeters (ECAG) (Ruess, 2011), and has hosted regular ECAG's since. The Walferdange laboratory has a large advantage over the BIPM site due to the ability to host a maximum of 16 absolute gravimeters simultaneously, whereas only 3-5 piers were used during comparisons at the BIPM site (Robertsson, et al., 2001) (Jiang, et al., 2012) (Vitushkin, et al., 2002). ...
Measuring the acceleration due to gravity at the NERC Space Geodesy Facility (SGF), Herstmonceux, provides a complimentary geodetic technique to the long established satellite laser ranging and global navigation satellite system measurements. The gravimetry measurements at the SGF were added to conform to the gravity field objective of the Global Geodetic Observing System and the European Combined Geodetic Network. Since both SLR and GNSS measurements are used in the computation of the International Terrestrial Reference Frame any un-modelled movements in the ground stations are undesirable. Gravity measurements can be used in the identification of such signals. This thesis reports the establishment of the technique at the SGF and contains a description of the installation experiences, a maintenance guide for the instrument and a comprehensive analysis of the gravity measurements over the ten years of operation to date, from 2006- 2016. Environmentally driven influences on the gravity measurements are investigated. The precision of the measurements are shown to be seasonally dependent and of varying magnitude. The hydrological influence on the gravity data from groundwater variation is calculated to be approximately 3.14 µGal, determined from temporal measurement of groundwater depth and an estimation of soil properties. A maximum influence from soil moisture content is estimated resulting in an influence of less than a microgal, which confuses correlation studies between local tide gauge data and an intermittent periodic signal seen in the gravity data. The high frequency data taken at the SGF highlights bias corrections two explainable and one of unknown origin. The bias corrections, of magnitude +1.5, -2 and -7.33 µGal, are shown to be critical to the interpretation of the time series, and, simulated campaign style measurements, using one set of measurements on an annual basis, prove that the data would be easily misinterpreted if the bias offsets found are not applied.
... Thus, the errors caused by the height reduction between 0.25 m and the ground level have been cancelled out. The uncertainties were determined analogously to Vitushkin et al. (2002) according to the following expression: ...
... where σ g(h) represents the standard deviation of absolute gravity measurement (at the height of measurement), u ins the instrumental uncertainty of the absolute measurement due to systematic errors (value of 40 nms -2 is taken as determined by Vitushkin et al. (2002)) and u dg(h) is the uncertainty of the reduction to the height of 0.25 m. ...
... In order to evaluate the instrumental uncertainties and check for existence of significant offsets in the absolute measurements, an analysis of the deviations of measurements of gravimeters FG5-101 and FG5-206 from the reference values of the ICAGs have been made based on the results of the ICAGs from 1994 to 2013 (Marson et al. 1995;Robertsson et al. 2001;Vitushkin et al., 2002;Jiang et al., 2011;Jiang et al., 2012;Francis et al., 2015). The deviations presented in Figure 4, in most cases, are not significant for gravimeter FG5-101 with respect to their uncertainties, while for both gravimeters the deviations are not consistent in time. ...
The paper presents the new joint adjustment of the Croatian First Order Gravity Network, for the first time adjusted as a whole. The adjustment involves absolute and relative gravity measurements, latter performed in the course of four survey stages. Firstly, the measurements are concisely described. Revision of the absolute and pre-processing of the relative measurements are briefly presented. The applied adjustment model is described. Accordingly, the gravity values of all stations (absolute and relative), corrections of linear calibration coefficient and linear drift coefficients are included in the functional model as unknown parameters. The absolute measurements are included in the adjustment as observations. The new adjustment resulted in significantly different gravity values as compared to previous adjustments (of individual stages of the network). The differences in gravity values are an order of magnitude greater than the expected accuracy. It is shown that the differences are mainly due to the errors in the gravimeters’ calibration constants, which were neglected in the previous adjustments. Because of the significant differences, the new linear transformation function from the Potsdam to the Croatian Gravity System is determined.
... For that purpose, gravity must be known, hence measured, at the 10 À8 level in laboratories housing a Kibble balance . Used as standards, absolute gravimeters must participate regularly in intercomparison campaigns to look for possible biases (Francis et al., 2015;Jiang et al., 2011;Pálinkáš et al., 2017;Vitushkin et al., 2002). ...
... Intercomparison campaigns (Francis et al., , 2013(Francis et al., , 2015Schmerge et al., 2012;Vitushkin et al., 2002) have shown that offsets between absolute gravimeters range commonly 100-220 nm/s 2 ( Figure A9). Hence, when absolute gravity measurements are performed, if different AGs are used in the same study, instrument differences should be included in the uncertainty budget (Mémin et al., 2011;Pálinkáš et al., 2013;Sato et al., 2006) or accounted for (Lambert et al., 2006;. ...
In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field.Time-variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the changing Earth. Ground-based gravimetry can determine the change in gravity related to the Earth rotation fluctuation, to celestial-body and Earth attractions, to the mass in the direct vicinity of the instruments, and vertical displacement of the instrument itself on the ground.
In this paper, we review the geophysical questions that can be addressed byground gravimeters used to monitor time-variable gravity. This is done in relation to the instrumental characteristics, noise sources and good practices. We also discuss the next challenges to be met by ground gravimetry,the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation.
... Average of self-attraction field ± 2.2 1.9 FEA self-attraction field result ± 2.3 0.5 should be evaluated. Figure 8 shows the historical g measurement differences from 2001 to 2009 based on comparison reference values (CRVs) [31][32][33]. To take the long-term g stability into account, we added an extended uncertainty component of 1.6 µGal, which covers all the measurement results (with uncertainties) of the CRVs. ...
The self-attraction effect needs to be evaluated and corrected towards a 10⁻⁹ level absolute determination of the local gravitational acceleration g in Kibble balance experiments. In this paper, the self-attraction effect of the BIPM Kibble balance apparatus is modelled by linking the gravitational field to the electrical field based on an electrostatic finite element analysis. A mapping of the gravitational field with different construction segments of the apparatus is presented, yielding a total correction of (4.7 ± 0.5) μGal at the mean trajectory position. Experimental measurements are carried out to check the self-attraction model. Based on the obtained result and previous measurements, we updated the g determination along the measurement trajectory for the forthcoming Planck constant measurement.
... Intercomparison campaigns [e.g. Francis et al., 2005;2010;2013;2015;Jiang et al., 2012;Schmerge et al., 2012;Vitushkin et al., 2002] showed that differences between FG5 and JILAg gravimeters are commonly of the order of 100-150 nm/s² . A difference as large as 461 nm/s² was reported for one of the A10 instruments that participated in the ICAG-2001 intercomparison [Vitushkin et al., 2002]. ...
... Francis et al., 2005;2010;2013;2015;Jiang et al., 2012;Schmerge et al., 2012;Vitushkin et al., 2002] showed that differences between FG5 and JILAg gravimeters are commonly of the order of 100-150 nm/s² . A difference as large as 461 nm/s² was reported for one of the A10 instruments that participated in the ICAG-2001 intercomparison [Vitushkin et al., 2002]. In other comparisons, systematic and random errors of A10 gravimeters ranged between 70 and 220 nm/s² [Jiang et al., 2011;Francis et al., 2005;2013;2015]. ...
We estimate the signature of the climate-induced mass transfers in repeated absolute gravity measurements based on satellite gravimetric measurements from the GRACE mission. We show results at the globe scale, and compare them with repeated absolute gravity (AG) time behavior in three zones where AG surveys have been published: Northwestern Europe, Canada and Tibet. For 10 yearly campaigns, the uncertainties affecting the determination of a linear gravity rate of change range 3-4 nm/s²/a in most cases, in absence of instrumental artefacts. The results are consistent with what is observed for long term repeated campaigns. We also discuss the possible artefact that can results from using short AG survey to determine the tectonic effects in a zone of high hydrological variability. We call into question the tectonic interpretation of several gravity changes reported from stations in Tibet, in particular the variation observed prior to the 2015 Gorkha earthquake.
... Let us say that the measured absolute gravity at the reference height is g rf . The absolute gravity value at a reduced height then becomes g rd = g rf +b (h rd − h rf )+c (h rd − h rf ) 2 , where b and c are first-and second-order gravity gradient coefficients (Vitushkin et al. 2002;Jiang et al. 2009Jiang et al. , 2011Jiang et al. , 2012a. In practice, it is usually assumed that the coefficients b and c are 3.086 and 0 μGal/cm, respectively. ...
... Hence, the pillar may cause some vibration during the FG5 measurements. When we excluded the FG5 outside stations, we obtained the differences at the inside stations to be between −3.9 and 5.5 μGal which are similar to the results reported by the other researchers (Vitushkin et al. 2002;Timmen 2010;Jiang et al. 2011Jiang et al. , 2012aFrancis et al. 2010Francis et al. , 2013Schmerge et al. 2012). ...
In order to define gravity datum and gravity scale in the Kingdom of Saudi Arabia (KSA), an absolute gravity network, called KSA Absolute Gravity Network (KSA-AGN), comprising of 25 sites distributed countrywide was observed from January 2013 to February 2013. Two stations were installed at each network site: one inside the building and one outside. Micro-g A10 (#029) portable absolute gravimeter was used for data acquisition of two setups of ten sets each at both inside and outside stations. Set scatters for A10 setups are usually less than ±3 μGal, and the differences between two setups vary in the range of −8 to 5 μGal. The weighted mean of the two setups were calculated as unique absolute gravity value and its uncertainty at the stations. Seven of the stations (five inside and two outside) were collocated by Micro-g FG5 (#111) absolute gravimeter having 24 sets for each setup. Set scatters for FG5 setups are less than ±4 μGal almost like A10 setups. However, we obtained the total uncertainty of FG5 and A10 measurement about ±2 and ±6 μGal, respectively. Furthermore, to reduce measured absolute gravity from the reference height to any height, gravity gradients over both inside and outside stations were measured by using two Scintrex CG5 (#922 and #924) relative gravimeters. Average CG5 gradient at the outside stations is about 3.1 μGal/cm, satisfying the free air gradient in the country. Differences between A10 and FG5 absolute gravities at 72 cm vary between −3.8 and 9.5 μGal at seven stations. Excluding the outside stations, we obtained the differences from −3.8 to 5.5 μGal at inside stations.
... The comparison of the absolute gravimeters (AGs) is the only way to realise the metrological calibration of the instruments or determine the degrees of equivalence (DoEs) between instruments. The A10-003 was tested at the Sixth International Comparison of Absolute Gravimeters (ICAG-2001) with the intention of testing how reliable and repeatable it was at several known absolute gravity sites, the differences between the g value obtained by A10-003 and the result of the combined adjustment of absolute and relative measurement data during ICAG-2001 was (−30.8 ± 12.3) µGal [4,5]. In the ICAG-2005, the A10-008 was also compared, and the offset of the A10-008 versus the Comparison Reference Value (CRV) was (−7.2 ± 3.3) µGal [6]. ...
The A10-022 absolute gravimeter is utilised to measure the gravitational acceleration (g) for the first time at the 24 sites of the six relative gravimeter calibration baselines (the required absolute standard uncertainty for 10 µGal, 1 µGal = 1 × 10−8 m s−2) in China. The A10-022 was firstly used in long-term indoor observations and compared with a FG5 absolute gravimeter. The analysis of the data indicates that the standard deviation of the measurements was 4.7 µGal, the maximum peak-to-peak gravitational acceleration was 16.9 µGal at the laboratory and the offset compared to the FG5-232 absolute gravimeter was less than 4 µGal. The expanded uncertainties of A10-022 are approximately 22.0 µGal combining the uncertainty of the KCRV (Key Comparison Reference Value), the stability of the reference absolute gravimeter (FG5-232 in this case) and the bias measured during the comparison. Since 2011, the experiment has been implemented at the Lushan (LS) relative gravimeter calibration baseline to detect the feasibility and technical requirements of the A10 in field absolute gravity measurements. The gravitational acceleration was measured using the A10-022 at five new calibration baselines in 2012. Finally, all of the data from the A10-022 were adjusted to the height (25 cm) of the CG-5 relative gravimeter to compare with the results of gravity differences from the CG-5 at the six baselines. The results indicate that the average bias and the standard deviation of the differences between the A10 and the relative gravity differences measured by CG-5 were 5.1 µGal and 2.8 µGal, respectively. The expanded uncertainty of the A10-022 measurements covers the average biases between the A10-022 and CG-5 for each calibration baseline.
... The results of the ICAGs in 1997 [20], 2001 [21], and 2005 [19] are compared in Fig. 2. These results are the weighted means of the individual results with all the absolute gravimeters transferred to site A (at the height of 0.9 m). ...
... Due to unknown true gravity values, gravity references and offsets must be periodically determined by means of the international comparisons of absolute gravimeters (ICAGs), see de Viron et al (2011). The last ICAGs held in Sèvres (Vitushkin et al, 2002;Jiang et al, 2011) and Walferdange (Francis et al, 2004 show the following standard deviations of offsets for the FG5 gravimeters: 4.3 µGal (Sèvres 2001), 1.8 µGal (Walferdange 2003), 3.2 µGal (Sèvres 2005), 2 µGal (Walferdange 2007). The ICAG's results clearly demonstrate that offsets of AGs are very important error sources in current absolute gravity measurements and that ICAGs allow for their determination with the precision of 1 µGal. ...
Since August 2001, the absolute gravimeter FG5#215 has been used for the modernization of the national gravity networks of the Czech Republic, Slovakia, and Hungary. Altogether 43 absolute stations were measured, some of them repeatedly. Absolute gravity at 29 stations had already been determined in 1990s by other absolute gravimeters (FG5 or JILAg). Differences of repeated measurements at most of the stations show an unexpected decrease of gravity (up to 22 μGal) over the whole region. An uncertainty assessment of absolute measurements with a special emphasis put on hydrological effects shows a statistical significance of the detected gravity variations at many stations. In this manuscript, three possible reasons of such findings are discussed: (1) a regional geodynamic activity, (2) systematic instrumental errors (offsets), (3) hydrological effects. The analysis and statistics of the gravity differences in context of international comparisons of absolute gravimeters show offsets up to 9μGal related to data of the JILAg-6 and FG5#107 gravimeters. Data collected in this study demonstrate that considering instrumental and hydrological effects on gravity are crucial for a correct interpretation of repeated absolute gravity measurements.
