Abstract

AbstractAbsolute gravity measurements taken on a near-weekly basis at a single location is a rarity. Twelve years of data at the UK’s Space Geodesy Facility (SGF) provides evidence to show that the application of results from international comparisons of absolute gravimeters should be applied to data and are critical to the interpretation of theSGF gravity time series of data from 2007 to 2019. Though residual biases in the data are seen. The SGF time series comprises near weekly data, with exceptions for manufacturer services and participation in international instrument comparisons. Each data set comprises hourly data taken over 1 day, with between 100 and 200 drops per hour. Environmental modelling indicates that the annual groundwater variation at SGF of some 2 m influences the gravity data by 3.1 μGal, based upon some measured and estimated soil parameters. The soil parameters were also used in the calculation of the effect of an additional telescope dome, built above the gravity laboratory, and have been shown to be realistic. Sited in close proximity to the long-established satellite laser ranging (SLR) system and the global navigation satellite systems (GNSS) the absolute gravimetry (AG) measurements provide a complimentary geodetic technique, which is non space-based. The SLR-derived height time series provides an independent measurement of vertical motion at the site which may be used to assess the AG results, which are impacted by ground motion as well as mass changes above and below the instruments.

Highlights

  • Characterisation of key geodetic sites for the improvement of their products is important for the demands of geodesy and the various reference frames which are built upon the data from the worldwide geodetic observatories

  • A comparison is made between the absolute gravity (AG) time series and station heights derived from satellite laser ranging (SLR)

  • The results indicate that instrument comparisons should be carried out as often as is practical for all users of FG5s

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Summary

Introduction

Characterisation of key geodetic sites for the improvement of their products is important for the demands of geodesy and the various reference frames which are built upon the data from the worldwide geodetic observatories. These features become of particular significance when important events such as changes to the instrumentation or environment are. In earlier work, the magnitude of the bias in 2013 was taken to be 7.3 Gal. Campaign Simulation be tempting to apply an offset for the 2013 to 2017 data and estimate a glacial isostatic adjustment (GIA) rate from the residual. Campaign Simulation be tempting to apply an offset for the 2013 to 2017 data and estimate a glacial isostatic adjustment (GIA) rate from the residual Such an interpretation would be critically flawed given our understanding of events in the whole SGF time series. Interpretation of these results could be critical for a country-wide project: it could

AG vs SLR Heights
Conclusion
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