AIPS HELP file for VLBAFPOL in 31DEC25

As of Fri Jun 20 19:53:54 2025

INPUTS

INNAME                             Input file name
INCLASS                            Input file class
INSEQ                              Input file sequence number
INDISK                             Disk number for input file
OUTDISK                            Disk number for output file
                                   (this disk must have enough
                                   free space to hold a copy of
                                   the input file).

          VLBAFPOL is defined in the VLBAUTIL run file.

HELP SECTION

VLBAFPOL
Type: Procedure
Use:  VLBAFPOL is a procedure that checks the polarization labels for
      VLBA data and either creates a new file that is labeled correctly
      or recommends a course of action.

      Type RUN VLBAUTIL to make the VLBAFPOL procedure available.

  INNAME.....The name of the file to be checked. Wildcard characters are
             allowed.
  INCLASS....The class of the file to be checked. Wildcard characters
             are allowed.
  INSEQ......The sequence number of the file to be checked. Zero
             defaults to the highest sequence number of a file matching
             INNAME, INCLASS, and INDISK.
  INDISK.....The disk drive number of the file to be checked. Zero
             defaults to any disk.
  OUTDISK....The disk drive number of a disk to hold the corrected data.
             This disk must have sufficient free space to hold a copy of
             the input file. Zero defaults to any disk.

EXPLAIN SECTION

VLBAFPOL:           Procedure to check VLBA polarizations
Documentor:         Chris Flatters
Related Programs:   VLBAUTIL, FXPOL

WHEN TO USE VLBAFPOL

Use VLBAFPOL to check whether you need to relabel the polarizations in
your data after loading the data, looking for subarrays, and merging
redundant calibration data but before reading any calibration data from
non-VLBA stations.

VLBAFPOL assumes that all of your FREQIDs have similar polarization
setups.  For this reason, you should normally run VLBAFPOL after copying
each frequency ID to a separate file. This may be done using VLBAFQS.
This strategy also reduces the amount of disk space needed for VLBAFPOL.

You should make sure that at least one disk has enough free space to
hold a copy of your data before running VLBAFPOL.

VLBAFPOL is intended for novice and experienced VLBA users.

WHAT VLBAFPOL WILL DO

VLBAFPOL will inspect your data to see if it appears to be a
dual-polarization data set labelled as having a single polarization.
It does this by checking the number of polarizations in the header and
by checking the frequency (FQ) table for IFs with the same frequency.
There are a number of possible outcomes.

* VLBAFPOL will do nothing because the header claims that the data
  already have more than one polarization.

* VLBAFPOL will do nothing because no two IFs have the same frequency
  and VLBAFPOL concludes that there is only one polarization present.
  This conclusion is incorrect if you have used an unusual set-up with
  different polarizations at different frequencies; if this is the case
  you may wish to run FXPOL manually to fix the labelling. You may also
  wish to run FXPOL manually to change the polarization labels from RR
  to LL or vice versa.

* VLBAFPOL will run FXPOL automatically because the IFs are all paired
  in frequency.  There is a small chance that VLBAFPOL will determine
  the output polarizations incorrectly.  If this happens then you will
  need to run FXPOL by hand.

* VLBAFPOL will no nothing because some but not all IFs are paired. This
  indicates that there is more than one polarization present but
  VLBAFPOL cannot guess how the polarizations should be mapped to IFs.
  In this case you need to run FXPOL manually.