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O=NOAO/IRAF V2.5 valdes@lyra Mon 15:42:35 12-Oct-87
\T=vt640
\G=vt640
clear\n\{%V-%!200\}
\n\{%10000
CCD REDUCTION DEMONSTRATION
In this demonstration we are going to make some (artificial) CCD
observations which we will reduce using the CCDRED package. The
dome is opening and we are ready to begin observing...\}
\n\{%V-\}
unlearn\sccdred;unlearn\sccdtest\n\{ # Initialize parameters and data...\}
imdelete\s%B%%*.*\sv-\n\{%V-\}
imrename\sB*.*\s%B%%*.*\sv-\n\{%V-\}
imdelete\sZero*.*,Flat*.*\n\{%V-\}
delete\sDemo*\sv-\n\{%V-\}
\n\{%V-\}
setinstrument\sdemo\sreview-\n\{ # Set instrument parameters...\}
lpar\sartobs\n\{ # List observing parameters...\}
artobs\sobs001\s0.\szero\n\{%15000 # Observe zero level images...\}
artobs\sobs002\s0.\szero\n\{%V-\}
artobs\sobs003\s0.\szero\n\{%V-\}
artobs\sobs004\s0.\szero\n\{%V-\}
artobs\sobs005\s0.\szero\n\{%V-\}
\n\{%V-\}
artobs.skyrate=0\n\{ # Observe a long dark count...\}
artobs\sobs006\s1000.\sdark\n\{%V-\}
\n\{%V-\}
artobs.filter="V"\n\{ # Observe V flat fields...\}
artobs.skyrate=2000\n\{%V-\}
artobs\sobs007\s1.\sflat\n\{%V-\}
artobs\sobs008\s1.\sflat\n\{%V-\}
artobs\sobs009\s1.\sflat\n\{%V-\}
artobs\sobs010\s1.\sflat\n\{%V-\}
artobs\sobs011\s2.\sflat\n\{%V-\}
artobs\sobs012\s2.\sflat\n\{%V-\}
\n\{%V-\}
artobs.filter="B"\n\{ # Observe B flat fields...\}
artobs.skyrate=1000\n\{%V-\}
artobs\sobs013\s1.\sflat\n\{%V-\}
artobs\sobs014\s2.\sflat\n\{%V-\}
artobs\sobs015\s3.\sflat\n\{%V-\}
artobs\sobs016\s3.\sflat\n\{%V-\}
artobs\sobs017\s3.\sflat\n\{%V-\}
artobs\sobs018\s3.\sflat\n\{%V-\}
\n\{%V-\}
artobs.filter="V"\n\{ # Observe objects...\}
artobs.skyrate=100\n\{%V-\}
artobs\sobs019\s10.\sobject\simdata=dev$pix\n\{%V-\}
artobs\sobs020\s20.\sobject\simdata=dev$pix\n\{%V-\}
artobs.filter="B"\n\{%V-\}
artobs\sobs021\s30.\sobject\simdata=dev$pix\n\{%V-\}
artobs\sobs022\s40.\sobject\simdata=dev$pix\n\{%V-\}
\n\{%V-\}
lpar\ssubsection\n\{ # Subsection readout parameters...\}
subsection\sobs023\sobs019\n\{%5000 # Readout a subsection of the CCD...\}
dir\n\{ # Check directory of observations...\}
clear\n\{%10000 # Continue...\}
\n\{%15000
INSTRUMENT SETUP
Because there are a variety of instruments, observatories, and data
formats there are many parameters. To set all of these conveniently
there is a task which reads setup files prepared by the observing
staff. The setup task:
1. Defines an instrument header translation file which
translates the image header parameters to something
the CCDRED package understands. This is an important
feature of the package.
2. It runs a setup script which sets parameters and performs
other functions desired by the observing staff.
3. The user is then given the opportunity to modify the
package and processing parameters...\}
\n\{%V-\}
setinstrument\smode=m\n\{ # Set demo instrument parameters...\}
demo\r
\{%5000\}^Z
\{%5000\}^Z
\{%5000\}\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
\r
Zero\r
\r
Flat*.*\r
^Z
clear\n\{%5000 # Continue...\}
\n\{%20000
IMAGE HEADERS
The CCDRED package uses image header information if present. This
includes the type of data (object, flat field, etc.), exposure
time, region of image containing the data, processing status, and
more. To make this more general there is a instrument header
translation file to translate image header keywords to the standard
names used by the package. In this example the image header
keywords are identical to the package except that the image type is
CCDTYPE, the exposure time is INTEG and the subset parameter is
FILTER. Let's look at the image header using the the standard
image header lister and the special one in the CCDRED package.
This special lister provides additional information about image
types and processing status...\}
\n\{%V-\}
imheader\sobs023\sl+\n\{ # List object image header...\}
ccdlist\sobs*.*\n\{%5000 # List short CCD status...\}
ccdlist\sobs023\sl+\n\{%5000 # List long CCD status...\}
clear\n\{%5000 # Continue...\}
\n\{%20000
COMBINE CALIBRATION IMAGES
In order to reduce calibration noise and eliminate cosmic ray events
we combine many zero level and flat field calibration images. The
combining task provides many options. We will combine the images by
scaling each image to the same exposure time, rejecting the highest
pixel at each image point, and taking a weighted average of the
remainder. Flat field images must be combined separately for each
filter. We will simply specify all the images and the task automatically
selects the appropriate images to combine! ...\}
\n\{%V-\}
zerocombine\smode=m\n\{ # Combine zero level images...\}
obs*.*\r
\{%5000\}^Z
flatcombine\smode=m\n\{ # Combine flat field images...\}
obs*.*\r
\{%5000\}^Z
clear\n\{%5000 # Continue...\}
\n\{%15000
PROCESS OBSERVATIONS
We are now ready to process our observations. The processing steps we
have selected are to replace bad pixels by interpolation, fit and
subtract a readout bias given by an overscan strip, subtract the zero
level calibration image, scale and subtract a dark count calibration,
divide by a flat field, trim the image of the overscan strip and border
columns and lines. The task which does this is "ccdproc". The task is
expert at reducing CCD observations easily and efficiently. It checks
the image types, applies the proper filter flat field, applies the
proper part of the calibration images to subsection readouts, does only
the processing steps selected if not done previously, and automatically
processes the calibration images as needed. As before we simply specify
all the images and the task selects the appropriate images to process
including finding the one dark count image "obs006". Watch the log
messages to see what the task is doing...\}
\n\{%V-\}
ccdproc\sobs*.*\n\{ # Process object images...\}
\n\{%V-\}
\{%V-\}q0,+,\r
NO\n\{%V-\}
\n\{%10000
That's it! We're done. Now lets check the results. The "ccdlist"
listing will show the processing status and the images are now smaller
and of pixel datatype real. The CCDSEC parameter identifies the relation
of the image to the actual CCD pixels of the detector...\}
\n\{%V-\}
ccdlist\sobs*.*\sccdtype=object\n\{ # List short CCD status...\}
ccdlist\sobs023\sl+\n\{%5000 # List long CCD status...\}
imhead\sobs023\sl+\n\{%5000 # List object image header...\}
dir\n\{%5000 # Check the data directory...\}
\n\{%V-
We specified that the original images be saved by using the prefix B.
We are also left with a text log file, a metacode file containing the
fits to the overscan regions, and a file which maps the filter subset
strings to short identifiers used in CCDLIST and when creating the
combined images "FlatV" and "FlatB". You may look through these files,
or use GKIMOSAIC to examine the metacode file, now if you want.
\}
|
