Investigations of a Suspected Jump in Swedish Repeated Absolute Gravity Time Series

Self Cite

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/s$$^2$$ 2 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.

Section: Figmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

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

Scherneck

Rajner

Engfeldt

2020

Self Cite

“…The variation of the bias of an instrument can be explained by a variety of factors. For example, Olsson et al (2016) show that a permanent change in the bias of a classical AG can occur during manufacturer service or unusual transport conditions (e.g. aviation transport).…”

Section: Gravimeter Bias and Si Traceabilitymentioning

confidence: 99%

Gravity field modelling for the Hannover 10 m atom interferometer

Schilling

Wodey

Timmen

et al. 2020

Absolute gravimeters are used in geodesy, geophysics and physics for a wide spectrum of applications. Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes. Users of absolute gravimeters participate in comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. However, since no measurement standard of higher-order accuracy currently exists, users of absolute gravimeters participate in key comparisons led by the International Committee for Weights and Measures. These comparisons provide the reference values of highest accuracy compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large-scale atom interferometers paves the way for a new measurement standard in absolute gravimetry used as a reference with a potential stability up to $$1\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 1 nm / s 2 at 1 s integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10-m-long interaction zone. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument’s uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We therefore established a control network for relative gravimeters and repeatedly measured its connections during the construction of the atom interferometer. We additionally developed a 3D model of the host building to investigate the self-attraction effect and studied the impact of mass changes due to groundwater hydrology on the gravity field around the reference instrument. The gravitational effect from the building 3D model is in excellent agreement with the latest gravimetric measurement campaign which opens the possibility to transfer gravity values with an uncertainty below the $${10}\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 10 nm / s 2 level.

“…Van Camp et al 2017), geodynamics (e.g. Olsson et al 2016) and geodesy (Pálinkáš et al 2013). In metrology, the highest requirements on g-values are related to the realization of the kilogram by the Kibble balance (Stock 2013;Robinson and Schlamminger 2016) where the absolute gravity has to be known at the centre of the test mass with accuracy better than 5 µGal (e.g.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of comparisons of absolute gravimeters using correlated quantities: reprocessing and analyses of recent comparisons

Pálinkáš

Wziontek

Vaľko

et al. 2021

Due to the lack of a natural reference for the absolute acceleration of free fall and gravity, absolute gravimeters are compared at international comparisons, where the gravity reference is realized based on a set of precise absolute measurements and the functional model for their processing. The main estimates of comparisons, specifically, the reference values, deviations of gravimeters (biases) and associated uncertainty estimates, are obtained by the method of constrained least squares. In this paper, based on data from six comparisons, we demonstrate and discuss the importance of several aspects that significantly influence the estimated parameters, such as the type of the constraint, the weighting schemes, the correlations between measurements or outlier detection. Following the state-of-the-art key comparisons in metrology, we are applying correlations between measurements of a particular gravimeter for the first time, showing the ability to obtain appropriate uncertainty estimates, strictly applying the law of error propagation. The processing of comparisons by the method of least squares is described step by step to provide a background for analyses of absolute gravimeter comparisons in the future, reflecting all specifics of these comparisons. Estimated parameters from uniformly elaborated comparisons represent an interesting statistical data set that has been used to analyse the significance of differences between FG5, FG5X and other types of gravimeters. We believe that the described method of processing, as well as the published results, will be especially useful in the realization of the International Gravity Reference System.