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

Abstract

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.

First evaluation of an absolute quantum gravimeter (AQG#B01) for future field experiments

“…Its sensitivity after 24 h of data integration is close to that of the iGrav. In low-noise environments, the AQG#B01 showed a sensitivity of 10 nm s −2 after 1 h. On multi-year timescales the performance of the AQG in comparison with superconducting gravimeters still requires evidence with respect to noise and the resolution of sub-daily to weekly phenomena (Scherneck et al, 2020). AQG#B01 g residuals showed no correlation with manually increased tilts nor increased temperatures.…”

Non-tidal ocean loading signals of the North and Baltic Sea from terrestrial gravimetry, GNSS, and high-resolution modeling

“…All datasets used within this study are publicly available. Gravity and barometric pressure data from the gravimeters iGrav 047 and gPhoneX 152 at Heligoland (Voigt et al, 2020) as well as from OSG 054 at Onsala (Scherneck et al, 2022), iGrav 033 at Serrahn (Reich et al, 2024) and iOSG 023 at Strasbourg (Boy et al, 2017) are available from the IGETS database hosted by the Information System and Data Center at GFZ (Voigt et al, 2016). Raw GNSS data are available from BKG (2024), while processed data are published by Deng (2023).…”

Non‐Tidal Ocean Loading Signals of the North and Baltic Sea From Terrestrial Gravimetry, GNSS, and High‐Resolution Modeling

“…All data sets used within this study are publicly available. Gravity and barometric pressure data from the gravimeters iGrav 047 and gPhoneX 152 at Heligoland (Voigt et al, 2020) as well as from OSG 054 at Onsala (Scherneck et al, 2022), iGrav 033 at Serrahn (Reich et al, 2024) and iOSG 023 at Strasbourg (Boy et al, 2017) are available from the IGETS database hosted by the Information System and Data Center at GFZ (Voigt et al, 2016). Raw GNSS data are available from BKG (2024), while processed data are published by Deng (2023).…”