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Astron. Astrophys. 356, 357-362 (2000)

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A GPS-based method to model the plasma effects in VLBI observations

E. Ros 1,2, J.M. Marcaide 1, J.C. Guirado 1, E. Sardón 3 and I.I. Shapiro 4

1 Departament d'Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, València, Spain
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 Deutsche Forschungsanstalt für Luft- und Raumfahrt e.V., Fernerkundungstation Neustrelitz, 17235 Neustrelitz, Germany
4 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

Received 17 September 1999 / Accepted 25 January 2000


Global Positioning System (GPS) satellites broadcast at frequencies of 1,575.42 MHz (L1) and of 1,227.60 MHz (L2). The dispersive property of the ionosphere can be used to combine independent measurements at the two frequencies to estimate the total electron content (TEC) between a GPS receiver site and a broadcasting satellite. Such measurements, made at sites near to Very Long Baseline Interferometry (VLBI) sites, can be used to estimate the ionospheric contribution to VLBI observables. For our 1991.9 astrometric VLBI experiment in which we obtained group-delay observations in the 8.4 and 2.3 GHz bands simultaneously, we found that the GPS and VLBI determinations of the ionosphere delays agreed with root-mean-square differences below 0.15 ns for intercontinental baselines and 0.10 ns for continental ones. We also successfully applied the GPS-based procedure to reduce the ionospheric effect in phase delays used for high precision differenced astrometry at 8.4 GHz for this same experiment.

Key words: plasmas – atmospheric effects – methods: observational – techniques: interferometric – astrometry

Present address: Grupo de Mecánica del Vuelo S.A., Isaac Newton 11, PTM Tres Cantos, 27860 Madrid, Spain

Send offprint requests to: E. Ros, (ros@mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000