AIPS HELP file for VLBACPOL in 31DEC22
As of Tue Dec 5 1:14:00 2023
VLBACPOL: Procedure to calibrate cross polarization delays
INNAME UV file name (name)
INCLASS UV file name (class)
INSEQ 0.0 9999.0 UV file name (seq. #)
INDISK 0.0 9.0 UV file disk drive #
OUTDISK Disk for temporary files
FLAGVER Flagging table
GAINUSE Prior calibration CL
SUBARRAY 0.0 99.0 Selected subarray
BASELINE List of antennas; MUST
REFANT Reference antenna; MUST BE
HIGHEST OR LOWEST NUMBERED
ANTENNA IN BASELINE LIST
CALSOUR Calibrator source to use
TIMERANG select time range with good
SNR for RL and LR corr.
SOLINT Solution interval (min)
0=> 10 minutes
DPARM for strong sources, it is
only necessary to set
DPARM(4)=the int. time (sec).
DPARM(1) and (8) are
automatically set by
for rest see HELP VLBACPOL
OPCODE 'AVIF' => avg SB delays
BADDISK Disk drive #'s to avoid
Procedure: This procedure uses a selected subset of a uv data set to
determine cross polarized multi- and single-band delays. The
average single-band and multi-band delays will be written into an
SN and CL table. See EXPLAIN VLBACPOL for details.
Before attempting to use VLBACPOL the RUN file VLBAUTIL must be run
to define the procedure. This is done by:
and only needs be done once.
VLBACPOL creates several temporary files which it will destroy if
able. The names of these files are fixed and must be destroyed if
a previous attempt at VLBACPOL failed. Also the output files must
not exist before running VLBACPOL. To execute the procedure simply
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 -> highest.
INDISK.....Disk drive # of input UV file. 0 -> any.
OUTDISK....Disk for temporary files 0=>INDISK.
FLAGVER....Flag table version to apply
GAINUSE....CL table from prior calibration to apply before
determining solutions. There is no default.
SUBARRAY...Subarray to use.
BASELINE...List of antennas, normally the reference antenna
and the others to be used, see EXPLAIN VLBACPOL.
NOTE: the reference antenna should have a number
either above or below ALL other antenna numbers.
REFANT.....Reference antenna. MUST BE HIGHEST OR LOWEST NUMBERED
ANTENNA LISTED IN BASELINE
CALSOUR....Calibrator source(s) to use.
TIMERANG...Time range of the data subset.
SOLINT.....The FRING solution interval (min), 0=> 10 minutes
DPARM......Delay rate parameters.
DPARM(1)...Number of baseline combinations to use in the initial,
coarse fringe search (1-3). Larger values increase the
point source sensitivity but reduce the sensitivity to
extended sources when an accurate model is not available.
0=>3. THIS PARAMETER IS AUTOMATICALLY SET TO 1 IN THIS
DPARM(2)...The delay window to search (nsec) centered on 0 delay.
0 => full Nyquist range defined by the frequency spacing.
If DPARM(2) < 0.0 no delay search will be performed.
DPARM(3)...The rate window to search (mHz) centered on 0 rate.
0 => full Nyquist range defined by the integration time.
DPARM(4)...The minimum integration time of the data (sec);
0 => search the data to find the minimum integration
The correct minimum of all baselines should be supplied.
DPARM(5)...If > 0 then don't do the least squares solution. If the
least squares solution is not done then only the coarse
search is done and much less accurate solutions are
DPARM(6)...If > 0 then the output data will not be averaged in
frequency else, all frequencies in each IF will be
averaged. Affects single source files only.
DPARM(7)...If > 0 then the phase, rate and delays will not be
re-referenced to a common antenna. This option is only
desirable for VLBI polarization data.
DPARM(8)...DPARM(8)>0 allows zero'ing of RATE, DELAY, and/or PHASE
solutions. ** Note that the ZEROing is done _AFTER_ the
FRING solution is found, this is not the mechanism for
turning off the DELAY, RATE, or PHASE search, see
DPARM(2-3) for that capability. **
DPARM(8) value zero RATES? zero DELAYs? zero PHASEs?
0 No No No
1 Yes No No
2 No Yes No
3 Yes Yes No
4 No No Yes
5 Yes No Yes
6 No Yes Yes
7 Yes Yes Yes
THIS PARAMENTER IS AUTOMATICALLY SET TO 1 IN THIS
OPCODE.....'AVIF' means average single band delays
corrections in IF, else do each IF independently.
The best value depends on the SNR.
BADDISK...Disk drive #'s to avoid for scratch files
VLBACPOL: Make an SN for the calibration of cross polarized
Documentor: W. D. Cotton
Related Programs: SWPOL, FRING, POLSN, CLCAL
Calibration of cross polarized delays
This procedure will take a selected subset of a uv data set
and determine the corrections needed to remove differences in
single and multiband delays for the right and left handed
systems. The output is an SN and CL. The output SN and CL tables
will be written to the input data set and on successful completion of
VLBACPOL will be the highest version SN/CL table. Cross polarized
rate errors are assumed to be zero.
This should run after correcting the instrumental delays (VLBAPCOR)
and before or after fringe fitting.
The basic steps of this procedure are the following:
1) Run UVCOP to select a short section of data for one or more
antennas and the reference antenna. This time/source/baseline
combination should have a reasonable SNR for the RL and LR
2) Run FRING on this segment of data to obtain corrections for
the parallel fringes. Use APARM=2,0; DOCAL=1; SNVER=1. Other
FRING parameters are as passed to the procedure either
explicitly in the inputs file or implicitly by the appropriate
3) Use CLCAL to apply this SN table to the CL table used to
calibrate the input to FRING.
4) Use SWPOL to swap the polarizations of the reference antenna.
Set ANTENNAS = ref. antenna; DOCALIB = 1
5) Run FRING as before but on the output of SWPOL. Do this once for
each antenna in the BASELINE array with the reference antenna.
6) Run POLSN on the SN table produced by FRING.
7) Use TACOP to copy the SN table produced by POLSN to the
original data set.
8) Run CLCAL to apply this SN table to the CL table given in
GAINUSE. There are 2 lines at the end which will state
which SN and CL tables contain the corrections.
This procedure will create a number of temporary files on
OUTDISK. These temporary files will have name 'CROSSPOL TMP'
and should be deleted by the procedure on successful completion.
As the names are fixed any residual files from a previous run of
CROSSPOL should be deleted before executing the procedure.