Figure 1: Schematic flow diagram of components relevant to BIMA software.
Figure 1: PS 11 Kb
Next: Development and Deployment of a Rule-Based Expert System for Autonomous Satellite Monitoring
Previous: Remote Observing and Automatic FTP on Kitt Peak
Table of Contents --- Search ---
PS reprint
W. Hoffman, J. Hudson
University of California, Berkeley
R. K. Sharpe
University of Illinois, Urbana-Champaign
A. W. Grossman, J. A. Morgan, P. J. Teuben
University of Maryland, College Park
The Berkeley-Illinois-Maryland Association (BIMA) operates a millimeter wave interferometer at Hat Creek, California. The array is an aperture synthesis instrument consisting of nine 6-meter diameter antennas which may be deployed in different configurations with spacings ranging from 7 meters up to 1.3 kilometers. At an observing frequency of 100 GHz, the three common configurations yield maps with angular resolutions of 5'', 2'', and 0.4'', over a 2' field. Larger fields must be mapped (``mosaiced'') by using multiple pointings. A technical description of the hardware details and scientific goals of the instrument can be found in Welch et al. (1996) and references therein.
The receivers may be tuned to any frequency in the 75--116 GHz range under full computer control. Each antenna contains a single dewar which accommodates up to four separate receivers.
Both the upper and lower sidebands of the first local oscillator are received and separated, providing two bands extending from 90--900 MHz on each side of the first local oscillator.
The correlation spectrometer covers a bandwidth of up to 800 MHz and provides up to 2048 channels for each antenna pair. There are four independently tunable spectral windows (in each sideband) allowing simultaneous observations of several different spectral lines. The spectral resolution ranges from 6 kHz (0.02 km/s) to 3 MHz (9 km/s).
With the expansion beyond the original three antennas, there have also been a number of major upgrades to the system, some of which have had a profound impact on the software system:
Figure 1: Schematic flow diagram of components relevant to
BIMA software.
Figure 1: PS 11 Kb
The correlator software has been completely rewritten in C++, with a C layer providing the interface to FORTRAN (the PROGRAM MAIN had to be done in FORTRAN). This precluded the use of the standard C++ I/O system, but close attention was given to the object model paradigm.
Control of the telescope is done through a number of standalone programs. Some common basic programs that perform basic operations include:
Most typical observing sessions involve four different sources: a passband calibrator (observed once); an amplitude calibrator (once); and an alternating phase calibrator and your source (both many times). Such basic observing programs with some sanity checks easily can consist of 100 lines of C-shell code. To simplify this process, and minimize errors made by astronomers, we decided to build a run-time processor that executes frequently-used constructs and also frees the observer from common sanity checking. Three basic commands were added:
The following is a very basic observing script that tunes the receivers, observes a passband source, and then alternates between observations of a calibrator and the main source.
# local setups
setup name=tuning cormode=4 corbw=50,50 corf=525,475,525,475
restfqs=115.2701 obsline=co
dopsrc=orimsr freq=115.2712 iffreq=500
setup name=all itime=30 elevlim=12 nchan=-1 stop=+24
setup name=passband setup=all source=3C454.3 vis=3C454.3 maxobs=1
setup name=calib setup=all source=0541-056 vis=0541-056 stop=+6
setup name=orimsr setup=all source=orimsr vis=orimsr nchan=1
# observing can commence: tune, do a passband and start the main loop
scan setup='tuning'
scan setup='passband'
loop srcsetup='orimsr' calsetup='calib'
Normally such scripts also contain comments describing the observations and messages designed to help the current observer.
The checker environment is an emulator of the on-line observing programs and runs completely independent of the on-line software system. In fact it also runs off-line in Maryland. Observers prepare their observing scripts and then run them through checker to look for syntax errors, spelling of source and calibrator (these names are stored in catalogs), and LST ranges. It also provided a summary of the observations of the sources and calibrators, observing efficiency, etc.
Datasets are archived in real-time at NCSA. A MIRIAD program extracts a limited set of fields (projectname, date, source, ra, dec, freq, etc.) from the datasets. A subset of this information is later used to help retrieve data from the archive. Archive retrieval is done directly through the WWW, using a CERN libwww based application that copies a tar file and extracts it on-the-fly at the client side.
BIMA also maintains a web site which contain various documents describing the array, how to apply for observing time, how to write observing scripts and check them, how to monitor data quality during the observation (astronomers are encouraged to be on-line during the observations, which are scheduled well in advance). From this home page the user can select a particular viewpoint of BIMA: an observer who wants to monitor progress at the site (restricted access); a programmer looking for subroutine documentation; an astronomer trying to calibrate and analyze data; etc. The ``observer'' page provides entry points to the most common operations a remote or prospective observer might want to do: check the current status of the interferometer, weather, etc., check the status at the archive and retrieve recent data; browse on-line documentation; etc.
Many members of the BIMA consortium have contributed to the on-line system. Part of this work is supported by the National Science Foundation.
Sault H., Teuben, P. J., & Wright, M. C. H. 1995, in Astronomical Data Analysis Software and Systems IV, ASP Conf. Ser., Vol. 77, eds. R. A. Shaw, H. E. Payne, & J. J. E. Hayes (San Francisco, ASP), p. 433