A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

Mamoru Sekido (1) , Kazuhiro Takefuji , Hideki Ujihara (1) , Tetsuro Kondo (1, 2) , Masanori Tsutsumi (1) , Eiji Kawai (1) , Hidekazu Hachisu (3) , Nils Nemitz (3) , Marco Pizzocaro (4) , Cecilia Clivati (4) , Federico Perini (5, 6) , Monia Negusini (5, 6) , Giuseppe Maccaferri (5, 6) , Roberto Ricci (4, 5, 6) , Mauro Roma (5, 6) , Claudio Bortolotti (5, 6) , Kunitaka Namba (3) , Jun’ichi Komuro (3) , Ryuichi Ichikawa (3) , Tomonari Suzuyama , Ken-Ichi Watabe , Julia Leute (7, 8) , Gérard Petit (7) , Davide Calonico (4) , Tetsuya Ido (3)

1 Kashima Space Technology Center
2 SHAO - Shanghai Astronomical Observatory [Shanghai]
3 NICT - National Institute of Information and Communications Technology [Tokyo]
4 INRiM - Istituto Nazionale di Ricerca Metrologica
5 IRA - Istituto di Radioastronomia [Bologna]
6 INAF - Istituto Nazionale di Astrofisica
7 BIPM - Bureau International des Poids et Mesures
8 SYRTE - Systèmes de Référence Temps Espace

We have developed a broadband VLBI (very long baseline interferometry) system inspired by the concept of the VLBI Global Observing System (VGOS). The new broadband VLBI system was implemented in the Kashima 34 m antenna and in two transportable stations utilizing 2.4 m diameter antennas. The transportable stations have been developed as a tool for intercontinental frequency comparison but are equally useful for geodesy. To enable practical use of such small VLBI stations in intercontinental VLBI, we have developed the procedure of node-hub style VLBI: In joint observation with a large, high sensitivity ‘hub’ antenna, the closure delay relation provides a virtual delay observable between ‘node’ stations. This overcomes the limited sensitivity of the small diameter node antennas, while error sources associated with large diameter antennas, such as gravitational deformation and delay changes in necessarily long signal cables, are eliminated. We show that this scheme does not result in an increased sensitivity to radio source structure if one side of the baseline triangle is kept short. We have performed VLBI experiments utilizing this approach over both short range and intercontinental distance. This article describes the system components, signal processing procedure, experiment, and results in terms of baseline repeatability. Our measurements reveal signatures of structure effects in the correlation amplitude of several of the observed radio sources. We present a model of the frequency-dependent source size for 1928+738 derived from correlation amplitude data observed in four frequency bands.

Domaines: Physique [physics]; Astrophysique [astro-ph]

Mamoru Sekido, Kazuhiro Takefuji, Hideki Ujihara, Tetsuro Kondo, Masanori Tsutsumi, et al.. A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept. Journal of Geodesy, 2021, 95 (4), ⟨10.1007/s00190-021-01479-8⟩. ⟨hal-03200998⟩