Benefits of non-tidal loading applied at distinct levels in VLBI analysis
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ORIGINAL ARTICLE
Benefits of non-tidal loading applied at distinct levels in VLBI analysis Matthias Glomsda1
· Mathis Bloßfeld1 · Manuela Seitz1 · Florian Seitz1
Received: 19 February 2020 / Accepted: 6 August 2020 © The Author(s) 2020
Abstract In the analysis of very long baseline interferometry (VLBI) observations, many geophysical models are used for correcting the theoretical signal delay. In addition to the conventional models described by Petit and Luzum (eds) (IERS Conventions, 2010), we are applying different parts of non-tidal site loading, namely the atmospheric, oceanic, and hydrological ones. To investigate their individual contributions, these parts are considered both separately and combined to a total loading. The application of the corresponding site displacements is performed at two distinct levels of the geodetic parameter estimation process (observation and normal equation level), which turn out to give very similar results in many cases. To validate our findings internally, the site displacements are provided by two different data centres: the Earth-System-Modelling group at the Deutsches GeoForschungsZentrum in Potsdam (ESMGFZ, see Dill and Dobslaw, J Geophys Res Solid Earth, 2013. https:// doi.org/10.1002/jgrb.50353)] and the International Mass Loading Service [IMLS, see Petrov (The international mass loading service, 2015)]. We show that considering non-tidal loading is actually useful for mitigating systematic effects in the VLBI results, like annual signals in the station height time series. If the sum of all non-tidal loading parts is considered, the WRMS of the station heights and baseline lengths is reduced in 80–90% of all cases, and the relative improvement is about − 3.5% on average. The main differences between our chosen providers originate from hydrological loading. Keywords VLBI · Non-tidal loading · Normal equation level · ESMGFZ · IMLS
1 Introduction Due to various geophysical processes, the positions of reference points fixed to the Earth’s crust change over time. When estimating the long-term linear motion of these points in the context of terrestrial reference frames (TRF), the instantaneous positions are regularized by subtracting a number of short-term periodic displacements. The conventional displacements are summarized in chapter 7.1 of the International Earth Rotation and Reference Systems Service (IERS) Conventions of 2010 (Petit and Luzum 2010) and include tidal effects at mainly diurnal and semi-diurnal periods. Displacements by non-tidal loading, however, are usually not applied. The latter is induced by rather local and irregular changes in atmospheric pressure and the mass redistribution of ocean or land water (hydrology). According to Petit and Luzum (2010), the modelling of non-tidal loading
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Matthias Glomsda [email protected] Deutsches Geodätisches Forschungsinstitut der Technischen Universität München (DGFI-TUM), Arcisstr. 21, 80333 Munich, Germany
is less accurate, and the impact on the geodetic parameters is less significant than for the conv
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