BIMA calibration requirements for AIPS++
AIPS++ User Specification Memo nr. xxx
(Peter Teuben, University of Maryland)
This memo reviews BIMA calibration requirements for AIPS++,
BIMA software development has concentrated on both the offline and
online software. The off-line software consists mainly of the
package (Sault et al. 1995), and is used by both BIMA and the ATNF. A
number of spin-offs (WIP, mxv) have also been produced by the
consortium. The X-windows based mxv data-cube vizualizer is currently
rewritten and available (in beta release) as aipsview from the Illinois
group. WIP is still maintained and available from the Maryland group.
The online software is mainly developed by the Berkeley group (with some
Maryland contributions, see also Hoffman et al. 1996). Although it
crucially depends on the MIRIAD libraries for it's user interface and
data I/O, it contains a number of system dependant modules (currently
running on Solaris 2.5 in a integrated Fortran/C/C++ environment) which
making porting a difficult task.
BIMA has recently completed it's 9-element array, including a
long-(1 km)-baseline project. Over the next year (effectively) two new
elements will be added to the array, polarization will be implemented,
and 1-mm receivers may be installed. Some of these developments are
described in the BIMA
BIMA special interests
Some of the listed items are tightly connected with ongoing hardware
development, and depend on it's individual time-line, which are not
all known at this time.
most likely this will be done in a
time-sliced fashion, measuring circular polarization (LR and RL) with
a quarter-wave plate. See also
for a discussion on some of the possibilities, and
for an implementation of the calibration procedure in MIRIAD.
This will likely have an impact on how flexible
the AIPS++ objects must be.
deconvolution of mosaiced fields. Various
techniques to calibrate these data will be tried out, and a flexible
setup of the resulting software is needed. For example, adding
a pointing parameter to the mosaic algorithm can greatly
improve the achievable dynamic range in a mosaiced image. Another
important obvious feature should be the ease with which
single dish data can be added to interferometry data.
BIMA regularly participates in mm VLBI experiments.
The phased array data are currently processed offline using
standard VLBI techniques (Mark-xxx, ref. xxx),
and whenever AIPS++ will provide VLBI data processing,
BIMA should be able to use them without any major
Unusual telescope modes:
We cannot assume that all telescopes in the array are the same. They
may have different sizes (primary beams). Currently though
all elements are 6m dishes.
Unusual correllator modes:
The correlator can be configured in many
modes, and produces DSB data with a small (< 8) number of windows with
different settings of the IF. An interesting method to calibrate
DSB data is to use the generally much slower varying gain ratio
(phase difference and amplitude ratio). Also wide band data should
not be treated different from narrow band data, and methods exists
to (re)compute one from the other. Individual flags shall be present
for each atomic correlation.
calibration: although some of the calibration will be done
online, we need a general offline calibration package. The DSB calibration
mentioned before is an example of a peculiar application.
Offline phase corrections, using total power measurements (see
Wright 1995b), examplify one of the many ways in which calibration
needs to be flexible.
Most of the functionality in MIRIAD should be available in AIPS++,
but we want to highlight a few specific items.
Visibility file format. MIRIAD employs a very general visibility file
format, where correlations (be it cross- or auto) are tagged
with a rich set of (name based) variables. Variables can be
multi-dimensional of any of the basic types (variables can change
dimension in a dataset, in principle even type).
Obviously, like in the FITS community, these variables need to be
registered and their meaning clarified. Currently MIRIAD knows
about 95 variables.
Although it would be ideal that the telescope data be directly
written in native AIPS++ format, for the forseable future we don't
see this happen. We expect to use a small conversion program,
while the "Telescope Management System" is being reviewed for
AIPS++ Consortium User Specifications (AIPS++ memo #115; 7-apr-92)
AIPS++ User Specifications: BIMA Version (AIPS++ memo #108, 1991)
- Welch, W.J. et al. 1996, PASP, 108, 93-103
- Wright, M.C.H., 1995a. "Polarization Switching for the BIMA array",
BIMA memo #43.
- Wright, M.C.H., 1995b.
"Atmospheric Phase Prediction from Total Power Measurements",
BIMA memo #44.
- Wright, M.C.H., 1996a. "Calibrating and Imaging Polarization Switched Data",
BIMA memo #48.
- W. Hoffman, J. Hudson, R. K. Sharpe, A.W. Grossman, J.A. Morgan, and
Real-Time Observing at Hat Creek,
in: Astronomical Data
Analysis Software and Systems V, ed. G.H. Jacoby and J. Barnes. PASP
Conf Series (in press, 1996).
- R.J. Sault, P.J.Teuben, and M.C.H.Wright.
A Retrospective View of Miriad,
in: Astronomical Data Analysis Software and Systems IV, ed. R.A. Shaw,
H.E. Payne and J.J.E. Hayes. PASP Conf Series 77, 433 (1995).
Last modified on 21-mar-1996. Please direct any comments on
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