AIPS HELP file for SNP2D in 31DEC20
As of Tue Jul 7 4:38:19 2020
SNP2D: Convert single-channel phase to delay in SN table
INNAME Input image name (name)
INCLASS Input image name (class)
INSEQ 0.0 9999.0 Input image name (seq. #)
INDISK 0.0 9.0 Input image disk unit #
INVERS Input table file version no.
OUTNAME Output image name (name)
OUTCLASS Output image name (class)
OUTSEQ -1.0 9999.0 Output image name (seq. #)
OUTDISK 0.0 9.0 Output image disk unit #.
BIF 1.0 IF of channel used in CALIB
in dataset INNAME
BCHAN 1.0 Channel in BIF used in CALIB
DOAPPLY -1.0 1.0 > 0 copy amplitudes in SN
else force amplitude to 1.0.
Task: In some cases, a strong spectral line is the best calibration
source available. With the wide bandwidth of modern
instruments, the phase measured at the frequency of the line
cannot be transferred directly to calibrate all other channels.
Instead, the measured phase needs to be interpreted as a delay
and that delay applied to all IFs (spectral windows).
Note that the antennas, source numbers, subarrays, frequency
IDs, etc. in the output file must exactly match those in the
input file. Otherwise, the information conveyed in the output
SN file will be confusing at best.
Note that the delay is simply the phase in turns divided by the
frequency of the spectral channel used to determine the phase.
This task determines the current frequency quite carefully
using the same code as CVEL. You must set a rest frequency in
the source table with SETJY if there is none to begin with.
WARNING: This task is to be used AFTER you have done as good a
job as possible with your absolute calibrator and your phase
reference calibrator. Run a FRING on the former to take out
gross delays and line up phases. Then run a FRING or CALIB as
a function of time on the phase reference calibrator. Then run
a CALIB on the reference spectral line preferably using a few
rounds of self-cal (unless you know it to be a point source).
SNP2D will then convert small phases into modest additional
delays as a function of time. If there is any issue of phase
wraps and the like, then this task will not do the right
thing. If you used CALIB rather than FRING on the phase
reference source, you may need to run CALIB again on that
source after SNP2D (and CLCAL of course).
INNAME.....Input image name (name). Standard defaults.
INCLASS....Input image name (class). Standard defaults.
INSEQ......Input image name (seq. #). 0 => 1.
INDISK.....Disk drive # of input image. 0 => any.
INVERS.....Version number of input SN table, 0 => highest
OUTNAME....Output image name (name). ' ' => INNAME
OUTCLASS...Output image name (class). ' ' => INCLASS
OUTSEQ.....Output image name (seq. #). 0 => INSEQ
OUTDISK....Disk drive # of output image. 0 => INDISK
BIF........IF in data set INNAME containing channel used in CALIB -
BCHAN......Spectral channel of BIF in INNAME used in CALIB -
DOAPPLY....The real and imaginary parts of the gain determine the
phase from which the output delay is computed. The
output gain will have zero imaginary part (no phase).
If DOAPPLY > 0, the output real part will be equal to the
amplitude in the SN table of BIF. Otherwise, the output
real part of the gain will be 1.0.