Imaging VGOS Observations and Investigating Source Structure Effects

The next-generation, broadband geodetic very long baseline interferometry system, named VGOS, is being developed globally with an aim to achieve 1 mm accuracy for station positions. Currently, the systematic errors in VGOS broadband delays are still about 20 ps. In this study, we demonstrate that it is feasible to make images directly from VGOS observations without the need of complicated calibrations and determine the source structure effects in VGOS broadband delays through the process of model fitting to the structure phases from our imaging results. Source structure effects are investigated in detail, and it is shown that the systematic errors in VGOS observations are well explained by these effects. For instance, the root-mean-square (RMS) closure delays of the observations of sources 0016 + 731 and 1030 + 415 are 24.9 and 50.2 ps in session VO0034, respectively; after correcting source structure effects based on the images, the RMS values of the residual closure delays are 5.5 and 10.1 ps. The jumps in delay observables with magnitudes of several hundreds of picoseconds are found to be caused by 2π phase shifts among the four bands due to strong source structure effects. The impact of the alignment of the images at the four frequency bands in VGOS is discussed. Our study provides a methodology for deriving images of radio sources at the four bands of VGOS observations and discusses the alignment of the images at the four bands, which is fundamental to mitigating these systematic effects.

Description

Funding Information: This research has made use of the Generic Mapping Tools package, the pgplot library, and the SAO/NASA Astrophysics Data System. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al., 2018 ). This research was supported by the Academy of Finland project No. 315721. Susanne Lunz is supported by the DFG Grant No. HE5937/2‐2. Funding Information: We would like to thank the two reviewers Sergei Bolotin and Arthur Niell for their helpful comments. The results reported in this study used the data owned by the International VLBI Service (IVS) and its international self-funded member organizations. We are grateful to the IVS VGOS stations at GGAO (MIT Haystack Observatory and NASA GSFC, USA), Ishioka (Geospatial Information Authority of Japan), Kokee Park (U.S. Naval Observatory and NASA GSFC, USA), McDonald (McDonald Geodetic Observatory and NASA GSFC, USA), Onsala (Onsala Space Observatory, Chalmers University of Technology, Sweden), Westford (MIT Haystack Observatory), Wettzell (Bundesamt f?r Kartographie und Geod?sie and Technische Universit?t M?nchen, Germany), and Yebes (Instituto Geogr?fico Nacional, Spain), to the staff at the MPIfR/BKG correlator center and the MIT Haystack Observatory correlator for performing the correlations and the fringe fitting of the data, to the NASA GSFC VLBI group for doing the geodetic solutions, and to the IVS Data Centers at BKG (Leipzig, Germany), Observatoire de Paris (France), and NASA CDDIS (Greenbelt, MD, USA) for the central data holds. Publisher Copyright: © 2021. The Authors.

Keywords

geodetic VLBI, imaging VGOS observations, source structure, VGOS

DOI

10.1029/2020JB021238

Citation

Xu, M H, Savolainen, T, Zubko, N, Poutanen, M, Lunz, S, Schuh, H & Wang, G L 2021, ' Imaging VGOS Observations and Investigating Source Structure Effects ', Journal of Geophysical Research: Solid Earth, vol. 126, no. 4, e2020JB021238 . https://doi.org/10.1029/2020JB021238

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https://urn.fi/URN:NBN:fi:aalto-202107017835

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[article-cris] Sähkötekniikan korkeakoulu / ELEC

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Imaging VGOS Observations and Investigating Source Structure Effects

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