This training school was held on March 2022. The aim of this training school was to prepare for the next generation of VLBI, both in terms of the technical development, but also in terms of conveying knowledge between generations of researchers. Currently, the VLBI technique is in a very exciting phase of renewal with equipment for the next generation VLBI technique, the VLBI Global Observing System (VGOS) being installed at several places world-wide. VGOS promises to become a significant improvement in accuracy for the VLBI results. Thus, VGOS will be of great importance for geosciences and global change research, e.g., the Global Geodetic Observing System (GGOS). At the same time, a new generation of VLBI researchers is emerging and efforts are necessary to convey research knowledge in VLBI to the new generation, both concerning the legacy system and the new system. This research school shall address these issues and provide the necessary training.
The IVS Training School was organized by the IVS Committee on Education and Training (IVS CTE, more information at IVS CTE webpage )
The program consist of lectures and exercises developed with emphases on new VLBI Global Observing System (VGOS).
The school program covers following topics
L01 Why do we do it? – A motivation for VLBI for Geodesy and Geosciences
This lecture gives a general overview of the role of Geodetic VLBI in Geodesy and Geoscience. It explains what geophysical phenomena we can observe and study with this technique. The introduction of the VGOS concept will be presented here. The IVS activity and its components will be introduced.
L02 What do we use to observe? – VLBI stations, radio telescopes, receivers, backends
This lecture will give overview on the VLBI equipment, specifically VGOS. We go through the whole signal chain, starting from the radio telescope and receiver that collect radio signal and ending with the digital backend, where signal is sampled and digitized.
L03 Signal and Instrument Calibration
The signals pass through various components of the receiving system before they are digitized and time tagged. The signals suffer from system delays which are neither constant nor predictable. In this lecture we focus on the signal calibration used in VGOS.
L04: How do we store and transport the data? – Data acquisition and transport
In this lecture we'll focus on the signal processing steps and the handling of the digital data that is the result of that. The speed at which this data is generated and its sheer volume pose interesting problems for capturing and handling. In order to make inter- and intracontinental VLBI work data from several stations needs to be combined, which introduces yet more possible dimensions of (in)compatibilities. After this lecture you should be better informed about what is "out there" and what tools and mechanism may exist to help address the challenges in contemporary high-bandwidth VLBI.
L05 Why do we do it? – A motivation for VLBI for Astrometry
The main advantage of the VLBI technique over other space geodetic techniques is that our sources do not move. This gives VLBI great long term stability for its applications such as geodesy, earth orientation, spacecraft navigation, differential astrometry and phase referencing. All of these applications require highly accurate global astrometry such as provides by the International Celestial Reference Frame (ICRF).
L06 What do we observe? – Radio sources
Tour of the radio sky with emphasis on the (extragalactic) sources that are used as celestial references for geodetic and astrometric VLBI. Overview of their characteristics and observational properties, including morphology on VLBI scales. Basics on the source physics. General principles behind VLBI imaging.
L07 How do we plan observations? – Scheduling
In this lecture, we will learn the basics of generating a VLBI observing plan, the so-called schedule. We will go through the theory of scheduling and discuss the necessary models and scheduling approaches. Furthermore, we will learn how to best evaluate schedules
L08 How do we estimate delays? – Correlation and fringe-fitting
The fundamental observable for geodetic and astrometric VLBI is the difference in arrival times (time delay) of a signal from an extragalactic radio source received at two (or more) radio observatories. In this lecture, you will learn how to estimate this time delay based on the theory of correlation and bandwidth synthesis.
L09 How do we model observations? – Geophysical modelling
In this lecture we will learn about how the delay is modelled during the analysis. Using the best possible information about station and source positions, Earth Orientation, local deformations and relativistic modelling, one tries to predict the measurement before comparing it to the real data. The used models are briefly introduced, with the main idea of getting an understanding of what is needed for analysis and in return of what VLBI is capable to measure.
L10: How do we model observations? – Signal Propagation
The description of the propagation of VLBI signals in the atmosphere is a major error source and needs close attention. While velocities in the ionosphere are frequency-dependent and handled in fringe-fitting with VGOS, propagation delays in the troposphere need to be modelled with the help of zenith delays and gradients. This lecture covers the standard settings and illuminates the expectations with VGOS settings.
L11 How do we analyze the data? – Data analysis for geodesy
The least-squares adjustment is one of the traditional approach used in geodetic VLBI analysis for the estimation of geodetic parameter. In this lecture we introduce observation equations, parameterization, constraints, ambiguity resolution and quality assessment used in the geodetic analysis. The targeted parameter estimation and global solution will be covered in this lecture.
EX-1 Exercise on technical aspects
In this exercise we consider number of technical aspects that affect the measurements.
EX- 2 Imaging
The imaging of astro-geo VLBI sessions tells us a lot about the astro-physics of our objects. This exercise be presented as a short tutorial on the imaging of the extragalactic radio sources.
In this exercise, we will make use of the theoretical knowledge we have learned in L07 and generate our first VLBI schedules. We start with a simple approach and will gradually increase the complexity and optimization. After each step, we investigate the generated schedule to better understand how certain settings influence our results. Finally, we will have a look at the current status of VGOS scheduling.
EX-4 Exercise on correlation and fringe-fitting
This exercise will give you hands-on experience with software tools to estimate VLBI delays from real and synthetic data.
EX-5 Exercise on data analysis
Introduction to nuSolve software. Preliminary data analysis of INT and 24hr sessions of S/X and VGOS observations.
Teaching team :
Rüdiger Haas (Chalmers University of Technology, Sweden)
Aletha de Witt (SARAO, South Africa)
Christopher Jacobs (JPL, USA)
Marjolein Verkouter (JIVE, Netherland)
Matthias Schartner (ETH Zurich, Switzland)
Lucia McCallum (University of Tasmania, Australia)
Johannes Böhm (TU Vienna, Austria)
John Gipson (NVI, Inc./NASA Goddard Space Flight Center, USA)
Sergei Bolotin (NVI, Inc./NASA Goddard Space Flight Center, USA)
Patrick Charlot (University of Bordeaux)
Frederic Jaron (TU Vienna, Austria)
For further information contact Nataliya Zubko (email@example.com)