1993 NRAO VLBI/VLBA Summer School

Very Long Baseline Interferometry
and the VLBA

Proceedings from the 1993 NRAO Summer School,
NRAO Workshop No. 22,
held in Socorro, New Mexico 23-30 June 1993
J. A. Zensus, P. J. Diamond, and P. J. Napier (Eds.)
ASP Conference Series, Vol. 82, 1995

This book is intended to serve two primary purposes: to provide an introduction and reference of the basic hardware and software concepts relevant for very long baseline interferometry (VLBI), and to describe the fundamental design properties, observing capabilities, and analysis approaches of the VLBA. The book should be useful for both experienced VLBI practitioners and novices to the field. We recommend two outstanding complementary texts: Interferometry and Synthesis in Radio Astronmy by A. R. Thompson, J. Moran, and G. W. Swenson, Jr., and Synthesis Imaging in Radio Astronomy, edited by R. A. Perley, F. R. Schwab, and A. H. Bridle (ASP Conference Series, Vol. 6).

Order Information

The proceedings are published (August 1995) and distributed by the Astronomical Society of the Pacific, Copyright © 1995. Orders can be placed by phone or fax (with credit card) directly to the ASP (Phone: 1-800-962-3412 or 1-415-337-2126, fax: 1-415-337-5205). The cost is $36.- for members of the ASP or participants of the summer school, and $40.- for non-members (plus shipping/tax).

The NRAO is not selling or distributing copies of the book.

Conference photo


Below are links to preprints of the individual chapters in this book (in Postscript format).

All material is Copyright © 1995, Astronomical Society of the Pacific. Please contact the authors for permission to reproduce in any way.

Part 1: Basic Theory

Interferometry and Coherence Theory
B. Clark bclark@nrao.edu
[PS:0.5 Mb]

A brief overview of the fundamental principles underlying radio interferometry is presented using the terminology of modern optics. This includes the fundamental equations of aperture synthesis, a definition of terms for interferometers, and a brief discussion of the problem of calibrating interferometer phase.

Correlator Theory
J. Romney jromney@nrao.edu
[PS:0.6 Mb]

This lecture presents the general concepts of correlation and spatial coherence functions, as they apply to VLBI and VLBI correlator implementations. A uniform treatment, based in the spectral domain, is applied to both the conventional lag and the spectral or FX correlator architectures. Parallel presentations of both architectures are given, including their strengths and weaknesses, although more emphasis is placed on the FX correlator because it is less familiar.

Imaging Concepts
T. Cornwell tcornwel@nrao.edu
[PS:5.7 Mb]

The three principal areas of imaging are discussed: Fourier-inversion, deconvolution, and self-calibration. The emphasis is on the major concepts in these areas. Other chapters in these proceedings cover the practical details of how one drives a particular imaging algorithm.

Part 2: The Very Long Baseline Array

VLBA Design: Goals and Implementation
P. Napier pnapier@nrao.edu
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The Very Long Baseline Array (VLBA) is a highly flexible radio telescope designed for research in high resolution astronomy and geodesy. It is intended to make the technique of Very Long Baseline Interferometry (VLBI) available to observers who are not experts in radio interferometry. The top-level design goals for the Very Long Baseline Array are discussed and details of the design and performance of the antennas are presented.

The VLBA Receiving System:Antenna to Data Formatter
R. Thompson athompson@nrao.edu
[PS:0.9 Mb]

Details of the design and performance are given for that part of the VLBA electronics system located between the output of the feeds and the input to the formatter. This includes low-noise receivers, hydrogen maser and local oscillators, IF and baseband frequency converters, digital samplers and the calibration system.

VLBA Data Flow: Formatter to Tape
A. Rogers arogers@wells.haystack.edu
[PS:1.1 Mb]

This chapter presents details of the design and performance of the formatter unit, which prepares digital data samples for recording, and of the tape recorders used to record the data collected at each VLBA site.

The VLBA Correlator
J. Benson jbenson@nrao.edu
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This chapter presents details of the design and the data processing capabilities of the VLBA correlator.

What the VLBA Can Do For You
C. Walker cwalker@nrao.edu
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This chapter gives a basic description of what can be done with the VLBA. First the types of observations for which the array was built are reviewed. The special characteristics of the array that facilitate such observations are described. Then the major factors that determine whether a particular experiment can be done are discussed in some detail. These factors are the resolution, uv coverage, sensitivity, and image quality.

Part 3: VLBI Data Analysis

Calibration Techniques for VLBI
J. Moran moran@cfa.harvard.edu and V. Dhawan vdhawan@nrao.edu
[PS:1.2 Mb]

This chapter discusses the various techniques used to calibrate the amplitude and phase of VLBI data. The effect of residual calibration errors on image quality is also considered.

Spectral Line VLBI
M. Reid reid@cfa.harvard.edu
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The special problems encountered when performing spectral-line VLBI observations are discussed in this Chapter. In particular, the usefulness of Fourier transforming measured visibility data with respect to time, delay or frequency for purposes of fringe detection and calibration is clarified.

Fringe Fitting
W. Cotton bcotton@nrao.edu
[PS:0.8 Mb]

The effects of errors in the model used by a VLBI correlator and ways to calibrate these errors are discussed. First, a relatively theoretical discussion of the causes, effects, and methods of correcting these correlator model errors are given. Later sections provide practical demonstrations of the effects and techniques for dealing with them.

Practical Data Analysis
P. Diamond pdiamond@nrao.edu
[PS:1.1 Mb]

Practical guidelines to data processing in AIPS are given.

Practical VLBI Imaging
C. Walker cwalker@nrao.edu
[PS:2.2 Mb]

Practical aspects of VLBI imaging are discussed, with emphasis on the choices of parameters. Particular attention is paid to the interaction between the parameter choices and both the image appearance and the fit of the model [PS:image) to the data. The process is illustrated using an image made from 13 cm data from a VLBA geodesy experiment.

Non-Imaging Data Analysis
T. Pearson tjp@astro.caltech.edu
[PS:1.5 Mb]

In many types of observation it is impossible or inappropriate to make an image from the visibility data. This chapter addresses ways of interpreting visibility data directly, with an emphasis on model-fitting techniques.

Part 4: Advanced VLBI Topics

Polarization VLBI
W. Cotton bcotton@nrao.edu
[PS:0.8 Mb]

Theoretical and practical aspects of imaging VLBI polarization data are discussed, with emphasis on linear polarization measurements.

Multi-Frequency Synthesis
J. Conway jconway@nrao.edu and R. Sault rsault@nrao.edu
[PS:0.8 Mb]

Theory and practice of the technique of multi-frequency synthesis (MFS) are described, with emphasis on its application to VLBA observations.

VLBI Phase Referencing
A. Beasley tbeasley@nrao.edu and J. Conway jconway@nrao.edu
[PS:0.4 Mb]

Phase-referencing allows phase calibration of VLBI data. Using regular observations of a nearby calibrator source, delay, delay-rate, and phase corrections can be derived and their effects removed from the target source visibility data. This technique allows imaging much weaker objects than is possible via fringe-fitting methods. We examine the main types of phase error in VLBI observations (geometrical, instrumental, atmospheric, and ionospheric errors), and we demonstrate how phase-referencing reduces or removes them. Maximum switching times and angles, and the image dynamic ranges and sensitivities achievable using phase-referencing are discussed.

Geodetic Measurements with VLBI
D. Shaffer dshaffer@bootes.gsfc.nasa.gov
[PS:0.7 Mb]

The intent of this chapter is to familiarize VLBI observers with some of the capabilities of geodetic VLBI as well as provide a brief introduction to planning and analyzing a geodetic experiment. I have assumed that in many cases the observer will be more interested in getting results than in acquiring a deep understanding of the software used and the science behind it. Somebody who is interested in becoming a geodesist, with all the understanding that implies, should attach himself/herself to one of the extant geodetic VLBI groups.

E. Fomalont efomalon@nrao.edu
[PS:11.7 Mb]

The special VLBI techniques used to obtain accurate absolute or relative positions of radio sources are discussed.

Part 5: Other Networks and Global VLBI

Global VLBI Networks
R. Schilizzi rts@nfra.nl
[PS:2.4 Mb]

Current and future characteristics of the European VLBI Network (EVN) are described, and a brief description of the Asia-Pacific Telescope (APT) is given.

Part 6: Planning a VLBI Observation

Practical Experiment Preparation
J. Wrobel jwrobel@nrao.edu
[PS:0.2 Mb]

A step-by-step guide to planning a VLBI imaging project is presented, with emphasis on practical aspects.

azensus@nrao.edu 15 June 1995