Large-scale strain-rates in Europe derived from observations in the European geodetic VLBI network

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Astrometry and geodesy with radio interferometry: experiments, models, results

Summarizes current status of radio interferometry at radio frequencies between Earth-based receivers, for astrometric and geodetic applications. Emphasizes theoretical models of VLBI observables that are required to extract results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the achievements of VLBI during the past two decades in reference frames, Earth orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys., Vol. 70, Oct. 199

Observed secular gravity trend at Onsala station with the FG5 gravimeter from Hannover

Annual absolute gravity measurements with a FG5 instrument were performed in Onsala Space Observatory by the Institute of Geodesy of the Leibniz Universität Hannover from 2003 to 2011 and have been continued with the upgraded meter FG5X in 2014. Lantmäteriet, Gävle, with their FG5 absolute gravimeter have visited Onsala since 2007. Because small systematic errors may be inherent in each absolute gravimeter, their measuring level and a resulting bias (offset) between the instruments must be controlled over time by means of inter-comparison. From 2007 to 2014, 8 direct comparisons took place well distributed over the time span. A complete re-processing of the absolute gravity observations with the Hannover instrument has been conducted to improve the reduction of unwanted gravity effects. A new tidal model is based on continuous time series recorded with the GWR superconducting gravimeter at Onsala since 2009. The loading effect of the Kattegat is described with a varying sea bottom pressure (water and air mass load) and has been validated with the continuous gravity measurements. For the land uplift,which is a result of the still ongoing glacial isostatic adjustment in Fennoscandia, a secular gravity trend of −0.22 μGal/yr was obtained with a standard deviation of 0.17 μGal/yr. That indicates a slight uplift but is still not significantly different from zero

Analysis of atmospheric loading computations

Modeling computations show that atmospheric loading can cause vertical displacements with a amplitude of 2-5 mm. The uncertainty associated to these computations can also be in the order of a few mm. There are, in fact, errors and artifacts in the surface pressure data, in the inverted barometer assumption and discrepancies on how the data are treated by the different softwares. These effects, for different reasons, limit the accuracy of loading predictions both in the long and short-term. Additionally, there is the problem of the reference frame in which the displacements must be presented: a frame fixed to the solid Earth or one fixed to the centre of mass of the combined solid Earth/atmosphere system. Although, at the moment, the GPS noise level on the estimate of the vertical component is still at the level of a few to several mm for daily solutions, it is important to improve the atmospheric loading computations in view of future GPS noise level reductions. In particular, efforts shall be undertaken to compare the results of different software packages. Examples are the atmospheric pressure loading time series available at the IERS Special Bureau for Loading, those provided by the NASA Goddard VLBI group and the time series obtained with the software packages OLFG and CARGA. The differences will be quantified and, where possible, the source of the discrepancies will be identified