Regional comparison of absolute gravimeters, EURAMET.M.G-K2 key comparison

In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeters were compared in November 2015. Four gravimeters were from different NMIs and DIs, they were used to link the regional comparison to the CCM.G.K2 by means of linking converter. Combined least-squares adjustments with weighted constraint was used to determine KCRV. Several pilot solutions are presented and compared with the official solution to demonstrate influences of different approaches (e.g. definition of weights and the constraint) on results of the adjustment. In case of the official solution, all the gravimeters are in equivalence with declared uncertainties. == Main text To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/M/G-K2/EURAMET.M.G-K2.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA)

Regional comparison of absolute gravimeters SIM.M.G-K1 key comparison

Twelve absolute gravimeters were compared during the regional Key Comparison SIM.M.G-K1 of absolute gravimeters. The four gravimeters were from different NMIs and DIs. The comparison was linked to the CCM.G-K2 through EURAMET.M.G-K2 via the DI gravimeter FG5X-216. Overall, the results and uncertainties indicate an excellent agreement among the gravimeters, with a standard deviation of the gravimeters' DoEs better than 1.3 μGal. In the case of the official solution, all the gravimeters are in equivalence well within the declared uncertainties. == Main text To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/M/G-K1/SIM.M.G-K1.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA)

Final report of EURAMET.M.G-K3 regional comparison of absolute gravimeters

The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in the spring of 2018.Here we present the list of the participants who actually performed measurements during the comparison, the data submitted by the operators as well as the results of the determination of the gravity as a function of height at the comparison sites. The measurement strategy is briefly discussed and the results of the data harmonization is documented. Finally, the results of the constrained least squares adjustment are presented including the degrees of equivalence of each gravimeter and the key comparison reference values.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).Export citation and abstract BibTeX RIS

A Gravimetric Support Network for Very Long Baseline Atom Interferometry

With the introduction of portable atom interferometers (AI), a genuinely independent method for the determination of g is available for the first time since the introduction of laser interferometer based instruments. Current AIs offer several advantages and already reach the accuracy of classical sensors. Additionally, a small number of stationary experiments were implemented for research in fundamental physics and geodesy. These instruments, extending the free fall distance of atoms to several meters, allow for longer evolution times of the wave function, thereby increasing the sensitivity of the AI compared to decimetres in portable devices. The construction of an AI with a 9 m interaction zone is currently being completed at Leibniz University Hannover. The knowledge of g and its gradient is required for the evaluation of systematic effects and uncertainties in AI experiments. Therefore, a gravimetric control network connected to one absolute gravimeter pier was established and repeatedly observed during the construction of the Very Long Baseline Atom Interferometry facility (VLBAI). Before the installation of the instrument, this network included the central axis of the VLBAI and one vertical off-axis parallel profile. The latter profile can also be observed during operation of the VLBAI. The effect of local gravity changes, e. g., hydrology, is comparable to 1 nm/s² on both axes. The gravimetric measurements serve as a reference during initial tests of the VLBAI. Repeated observations in the future will be used to characterize the effect of local hydrology and other mass variations along the vertical axis. A model of the research building and groundwater level monitoring supplements the gravimetric network. As the VLBAI is capable of measuring g and its vertical gradient with higher accuracy (<1 nm/s²) than classical instruments, the model will be used to transfer g to a gravimetry laboratory for gravimeter comparisons. We present our strategy for gravimetric control of the VLBAI. This will provide a reference at first and will later be used to establish the VLBAI as a reference for gravimeter comparisons. The results of the first gravimetric campaigns and the comparison with the model of the VLBAI environment show an agreement within the instrumental uncertainties of the relative gravimeters used

Experimental assessment of the speed of light perturbation in free-fall absolute gravimeters

Precision absolute gravity measurements are growing in importance, especially in the context of the new definition of the kilogram. For the case of free-fall absolute gravimeters with a Michelson-type interferometer tracking the position of a free falling body, one of the effects that needs to be taken into account is the speed of light perturbation due to the finite speed of propagation of light. This effect has been extensively discussed in the past, and there is at present a disagreement between different studies. In this work, we present the analysis of new data and confirm the result expected from the theoretical analysis applied nowadays in free-fall gravimeters. We also review the standard derivations of this effect (by using phase shift or Doppler effect arguments) and show their equivalence

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

Postglacial 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

Indoor height determination of the new absolute gravimetric station of L'Aquila

In this paper we describe all the field operations and the robust post-processing proceduresto determine the height of the new absolute gravimetric station purposely selected to belong to a new absolute gravimetric network and located in the Science Faculty of the L’Aquila University. This site has been realized indoor in the Geomagnetism laboratory, so that the height cannot be measured directly, but linking it to the GNSS antenna of AQUI benchmark located on the roof of the same building, by a classical topographic survey. After the topographic survey, the estimated height difference between AQUI and the absolute gravimetric site AQUIgis 14.970±0.003 m. At the epoch of the 2018 gravimetric measures, the height of AQUI GNSS station was 712.974±0.003 m, therefore the estimated ellipsoidalheight of the gravimetric site at the epoch of gravity measurements is 698.004±0.005 m. Absolute gravity measurements are referred to the equipotential surface of gravity field, so that the knowledge of the geoidal undulation at AQUIg allows us to infer the orthometric height as 649.32 m

Superconducting gravimeter and seismometer shedding light on FG5’s offsets, trends and noise: what observations at Onsala Space Observatory can tell us

Ten-year worth of absolute gravity (AG) campaigns at Onsala Space Observatory (OSO), Sweden, are simultaneously reducedusing synchronous data from a superconducting gravimeter (SG). In this multi-campaign adjustment, the a priori modelscommonly applied for each setup in AG-alone experiments are sidestepped in favour of SG records and a model to estimateits drift. We obtain a residual (hourly samples) at the 5 nm/s2 RMS level, reducing the SG data with a range of ancillary datafor the site’s exposure to ocean and atmospheric loading, and hydrology effects. The target quantity in AG projects in theBaltic 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 ofinternational comparison campaigns of FG5 instruments. Two of these have been campaigning at OSO since 2009 when theSG 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’sscale factor when campaigns are evaluated one by one. The simultaneous adjustment afforded us an SG scale factor verynear the result from a campaign with a prototype quantum gravimeter.Whence, we propose that single-campaign results maybe biased and conjectures into their variation, let alone its causes misleading. The OSO site appears to present manageableproblems as far as environmental influences are concerned. Our findings advocate the use of AG instruments and proceduresthat are more long-term stable (reference realization), more short-term stable too (setup drifts), less service craving and moreresilient to microseismic noise

Using a Superconducting Gravimeter in Support of Absolute Gravity Campaigning — A Feasibility Study

Preparing for joint analysis of absolute gravity (AG) campaigns, this report investigates whether astationary superconducting gravimeter (SCG) can provide a long-term stable measurement of sitedependentperturbations 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 physicalorigin, where biasses in the inferred long-term drift rate may offset the rate that the reduced AG campaignsdeliver. Thus, the main objective is to include a set of gravity models and proxy series as completeas possible in the SCG analysis. Findings indicate consistency for dg/dt in the drift model at the 0.5 nm/s2/yrlevel using observations at Onsala Space Observatory from 2009 to 2017. In pursuit of the overridingobjective to improve the accuracy of secular rates of gravity owed to Glacial Isostatic Adjustment, ourapproach may even put numbers on a range of long-term changes due to atmosphere, hydrology, andnon-tidal ocean loading, namely the rate biasses reported here

Postglacial gravity change in Fennoscandia - three decades of repeated absolute gravity observations

For the first time, we present a complete, processed compilation of all repeated absolute gravity (AG) observations in the Fennoscandian postglacial land uplift area and assess their ability to accurately describe the secular gravity change, induced by Glacial Isostatic Adjustment (GIA). The dataset spans over more than three decades and consists of 688 separate observations at 59 stations. Ten different organisations have contributed with measurements using 14 different instruments. The work was coordinated by the Nordic Geodetic Commisson (NKG). Representatives from each country collected and processed data from their country, respectively, and all data were then merged to one dataset. Instrumental biases are considered and presented in terms of results from international comparisons of absolute gravimeters. From this dataset, gravity rates of change (g_dot) are estimated for all stations with more than two observations and a timespan larger than two years. The observed rates are compared to predicted rates from a global GIA model as well as the state of the art semi-empirical land uplift model for Fennoscandia, NKG2016LU. Linear relations between observed g_dot and the land uplift, h_dot (NKG2016LU), are estimated from the absolute gravity observations by means of weighted least squares adjustment (WLSA) as well as weighted orthogonal distance regression (WODR). The empirical relations are not significantly different from the modelled, geophysical relation g_dot = 0:03 - 0:163(+-0.016)h_dot. We also present a g_dot -model for the whole Fennoscandian land uplift region. At many stations, the observational estimates of g_dot still suffer from few observations and/or unmodelled environmental effects (e.g. local hydrology). We therefore argue that, at present, the best predictions of GIA-induced gravity rate of change in Fennoscandia are achieved by means of the NKG2016LU land uplift model, together with the geophysical relation between g_dot and h_dot