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Chan, S. J., Persson, S. E., McMahon, R. G., Mackay, C. D., Ellis, R., Beckett, M. G., & Hoenig, M. 1999, in ASP Conf. Ser., Vol. 172, Astronomical Data Analysis Software and Systems VIII, eds. D. M. Mehringer, R. L. Plante, & D. A. Roberts (San Francisco: ASP), 502
CIRSI Data Reduction System - CIRDR
S. J. Chan1,
S. E. Persson2,
R. G. McMahon3, C. D. Mackay4,
R. Ellis5, M. G. Beckett6,
M. Hoenig7
Abstract:
We report on our on-going software project CIRSI Data Reduction System,
which has been developed under the IRAF environment. This is a compact
infrared processing and analysis software system for a wide-field infrared
camera, the Cambridge Infrared Survey Instrument (CIRSI). It contains
four subpackages for quick-look analysis during real-time
observing, preprocessing, basic reduction and useful tools. This system can
handle a large amount of raw
data which can be pre-processed and reduced automatically during
real-time observations.
CIRSI is based on 4 Rockwell HAWAII 1024 x 1024 detectors. It contains no
cold optics other than a cold filter wheel inside a dewar. It
operates from 0.8 to 1.8 m (Z to H band) on non-infrared
optimized telescopes, with a planned upgrade for K band operation in 1999. The image
scales are dependent on the telescopes to be used (e.g.,
045/pixel on the 2.5 m Isaac Newton Telescope
(INT) f3.3 Prime and
032/pixel on the 4.2 m William Herschel Telescope
f2.8 Prime).
A single channel CCD controller is used to multiplex the 16 outputs
(4 outputs per chip) into a single pre-amplifier and signal processing
data chain. The camera control software, PIXCEL, runs under Windows 95
(Beckett et al. 1998).
There are two read-out modes from the camera which are Reset-Read-Read
Sampling (RRR) and Non-Destructive Read or Sloping Sampling (NDR, see
Fig. 1, Fowler & Gatley 1991).
CIRDR is a data reduction and analysis system for reducing and analysing data
obtained from CIRSI. It is written under the IRAF environment. The programming
languages which are being used in this system are IRAF-CL, IRAF-SPP
(IRAF subset preprocessor language), Fortran and C-shell scripts. In the
current version (version 0.0.3), there are four packages (see Fig. 2) which are
CQLOOK (CIRSI Quick Look Data Reduction Package) for producing rough sky
subtracted images from sets of dithered observations during an observation run,
CPLINE (CIRSI Pipeline Data Reduction Package) for producing
second pass/final-version of sky subtracted images,
CIRUTIL (CIRSI General Toolkit
Package) and CIRCONTRIB (CIRSI General Contribution Package).
On-line help is available in all active subpackages and sub-subpackages.
Two on-line introductory user guides, CIRSI User Guide and
CQLOOK User Guide,
are also available.
CQLOOK is the most developed package in this system. It is used
for producing rough sky subtracted images from sets of dithered
observations during an observation run. Because the observations are in the
near-infrared, the strong and variable sky background
requires dithering of many short exposures and the recombination of the
images with careful sky subtraction to produce deep images.
There are two active subpackages which are for basic preprocessing in order to
produce real astronomical images (CPREPROC) and for quick (first
pass)
data reduction to produce rough sky subtracted, dithering-mosaic
images (CREDUCT), as well as tasks for the first INT run (CINT1).
The file handling system uses a system-level approach which is an
object-oriented like infrastructure. The advantages of this design are
that it is simple and
portable, as well as that it has a compact structure on a solid foundation. The main
functionality is in the first level. Handling files from quadrants and/or
chips as well as read-out modes are in the second and third levels.
The automatic processing is in the 4th level.
Quick processing tasks can be used during real time observation,
normal data reduction at a telescope, or at a home institute.
There are two master programs (CNDRPROC, CRRRPROC) to process data
automatically for quick look purposes. They can
process data from 1 to 4 chips, 1 to 16 quadrants,
one selected chip, or one selected quadrant. There are several display
tasks to examine fields and two tasks to check saturation levels. Tasks for
pre-processing can get raw data from a data reservoir in which
raw data are stored.
There
are two tasks for making a mosaic image (dithering or offset) (see Fig. 3).
Both are interactive and semi-automatic.
Tasks for making flats are based on all currently available methods
which are domeflat, twilight-sky flat, and moving-sky flat. There are
at least two tasks for making bad pixel masks. For extra flexibility,
users may enter their own parameters for making calibration images and
sky images. Furthermore, tasks are also available to automatically
suppress objects in images
and to make second pass sky images.
Uniform stripe noise appears in images (Fig. 4a). The current correction
methods in the system are based on a linear median filtering method. There are
two typical problems occurring in the current algorithms which are ghost
stripes caused by bright objects within images (Fig. 4b) and the size of
bright objects are decreased and faint objects are smoothed out (Fig. 4c).
An improved method, which can eliminate the above problems, is based on a
second pass linear median filtering method (Fig. 4d).
Figure 1:
The read-out mode in CIRSI.
|
Figure 2:
CIRSI Data Reduction System flowchart.
|
Figure 3:
The center field of M51 in the H band. It was obtained
during June 1998 CIRSI commissioning run at the INT with 4 offset
pointings (447
) and 3 ditherings
(235). Exposure time is 12 minutes.
|
Figure 4:
Noise correction: (a). no correction, (b) and
(c). current
noise correction methods in the system, (d). second pass linear
median filtering method.
|
Acknowledgments
S. J. Chan thanks the Program Organizing Committee of
the Eighth Annual Conference on Astronomical Data Analysis Software
and Systems for offering her full financial support to attend the
conference.
References
Beckett, M. G., Mackay, C. D., McMahon, R. G.,
Parry, I. R., Ellis, R. S., Chan, S. J., & Hoenig, M. 1998, in SPIE Proc., Vol.
3354, ed. A. M. Fowler (Bellingham: SPIE), 431
Fowler, A. M., & Gatley, I. 1991, in SPIE Proc., Vol. 1541, Infrared
Sensors: Detectors, Electronics, and Signal Processing, ed. T. S. Jayadev, (Bellingham: SPIE), 127
Footnotes
- ... Chan1
- Institute of Astronomy, University of Cambridge,
Cambridge, U.K.
- ... Persson2
- Carnegie Observatories, Pasadena, California, U.S.A.
- ... McMahon3
- Institute of Astronomy, University of Cambridge,
Cambridge, U.K.
- ... Mackay4
- Institute of Astronomy, University of Cambridge,
Cambridge, U.K.
- ... Ellis5
- Institute of Astronomy, University of Cambridge,
Cambridge, U.K.
- ... Beckett6
- Carnegie Observatories, Pasadena, California, U.S.A.
- ... Hoenig7
- Institute of Astronomy, University of Cambridge,
Cambridge, U.K.
© Copyright 1999 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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