VLBI: A fascinating technique for geodesy and astrometry

Abstract

a b s t r a c tSince the 1970s Very Long Baseline Interferometry (VLBI) has proven to be a primary space-geodetic technique by determining precise coordinates on the Earth, by monitoring the variable Earth rotation and orientation with highest precision, and by deriving many other parameters of the Earth system. VLBI provides an important linkage to astronomy through, for instance, the determination of very precise coordinates of extragalactic radio sources. Additionally, it contributes to determining parameters of relativistic and cosmological models. After a short review of the history of geodetic VLBI and a summary of recent results, this paper describes future perspectives of this fascinating technique. The International VLBI Service for Geodesy and Astrometry (IVS), as a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU), is well on its way to fully defining a next generation VLBI system, called VLBI2010. The goals of the new system are to achieve on scales up to the size of the Earth an accuracy of 1 mm in position and of 0.1 mm/year in velocity. Continuous observations shall be carried out 24 h per day 7 days per week in the future with initial results to be delivered within 24 h after taking the data. Special sessions, e.g. for monitoring the Earth rotation parameters, will provide the results in near real-time. These goals require a completely new technical and conceptual design of VLBI measurements. Based on extensive simulation studies, strategies have been developed by the IVS to significantly improve its product accuracy through the use of a network of small (∼12 m) fast-slewing antennas. A new method for generating high precision delay measurements as well as improved methods for handling biases related to radio source structure, system electronics, and deformations of the antenna structures has been developed. Furthermore, as of January 2012, the construction of ten new VLBI2010 sites has been funded, with good prospects for one dozen more antennas, which will improve the geographical distribution of geodetic VLBI sites on Earth and provide an important step toward a global VLBI2010 network. Within this paper, the Global Geodetic Observing System (GGOS) of the IAG will also be introduced and the contribution of VLBI to GGOS will be described.

The effects of frequency-dependent quasar variability on the celestial reference frame

“…For example, the next generation VLBI system, the VLBI Geodetic Observing System (VGOS), aims to measure station positions to 1 mm accuracy, and station velocities to 0.1 mm year −1 (Niell et al, 2006;Petrachenko et al, 2009). This is an order of magnitude better than current measurements (Schuh & Behrend, 2012;Lovell et al, 2013). Clearly, many systematic and stochastic sources of error will need to be eliminated, or at least substantially mitigated to reach this goal.…”

Structure of the nucleus of 1928+738

“…The corresponding coordinate time series (Fig. 8), computed after observations of the geodetic VLBI monitoring program of the International VLBI Service for Geodesy and Astrometry (IVS; Schuh & Behrend 2012;Lambert priv. comm.…”

On the estimation of a celestial reference frame in the presence of source structure

“…We use the schedules of one year of standard geodetic VLBI sessions, the 2013 rapid turnaround sessions (R1, R4) of the International VLBI Service for Geodesy and Astrometry (IVS; Schuh & Behrend 2012). These R-sessions are undertaken twice a week for 24 h, using a global antenna network of 7-11 stations that can change from one session to the next (e.g.…”