Very Long Baseline
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).
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.
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 email@example.com
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.
J. Romney firstname.lastname@example.org
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.
T. Cornwell email@example.com
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
Part 2: The Very Long Baseline Array
VLBA Design: Goals and Implementation
P. Napier firstname.lastname@example.org
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
The top-level design goals for the Very Long Baseline Array are
discussed and details of the design and performance of the antennas
The VLBA Receiving System:Antenna to Data Formatter
R. Thompson email@example.com
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 firstname.lastname@example.org
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
The VLBA Correlator
J. Benson email@example.com
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 firstname.lastname@example.org
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 email@example.com and V. Dhawan firstname.lastname@example.org
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 email@example.com
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.
W. Cotton firstname.lastname@example.org
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 email@example.com
Practical guidelines to data processing in AIPS are given.
Practical VLBI Imaging
C. Walker firstname.lastname@example.org
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 email@example.com
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
Part 4: Advanced VLBI Topics
W. Cotton firstname.lastname@example.org
Theoretical and practical aspects of imaging VLBI
polarization data are discussed, with emphasis on linear polarization
J. Conway email@example.com and R. Sault firstname.lastname@example.org
Theory and practice of the technique of multi-frequency
synthesis (MFS) are described, with emphasis on its application to VLBA
VLBI Phase Referencing
A. Beasley email@example.com and J. Conway firstname.lastname@example.org
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 email@example.com
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 firstname.lastname@example.org
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 email@example.com
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 firstname.lastname@example.org
A step-by-step guide to planning a VLBI imaging project is
presented, with emphasis on practical aspects.
email@example.com 15 June 1995