AIPS NRAO AIPS HELP file for VLBAAMP in 31DEC21



As of Tue Oct 19 10:03:26 2021


VLBAAMP: Applies a-priori amplitude corrections

INPUTS

INNAME                             Input file name
INCLASS                            Input file class
INSEQ                              Input file sequence number
INDISK                             Disk number for input file
SUBARRAY                           Subarray to correct. 0=>ALL
ICHANSEL                           Array of start and stop chn
                                   numbers, plus a channel
                                   increment and IF to be used
                                   for channel selection in the
                                   averaging in ACSCL.
                                   Default = central 75 percent of band
DOFIT                              Fit for opacity correction
BADDISK                            Disks to avoid for scratch

          VLBAAMP is defined in the VLBAUTIL run file.

HELP SECTION

VLBAAMP
Type: Procedure
Use:  VLBAAMP is a procedure that applies post-bandpass and delay
      calibration amplitude correction and a-priori amplitude corrections.
      These corrections are added to the corrections in the highest
      numbered CL table.

      VLBAAMP assumes that you already have GC and TY tables and that you
      have at least one CL table.

      Type RUN VLBAUTIL to define the VLBAAMP procedure.

  INNAME.....The name of the file to be corrected. Wildcard characters are
             allowed.
  INCLASS....The class of the file to be corrected. Wildcard characters are
             allowed.
  INSEQ......The sequence number of the file to be corrected. 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 corrected. Zero defaults
             to any disk.
  SUBARRAY...The subarray to correct. Zero defaults to doing all.
  ICHANSEL...Array of start and stop channels plus a channel increment
             and IF, used to select the channels to be averaged.  For
             instance, if you wished to exclude channels 1 - 10 and
             121 - 128 because of bandpass effects, and channels 56 -
             80 of IF 1 but not IF 2 because of interference, then you
             would set ICHANSEL = 11,55,1,1, 81,121,1,1, 11,121,1,2.
             If you only wished to use every other channel from the
             second IF then you would set ICHANSEL = 11,55,1,1,
             81,121,1,1, 11,121,2,2.  Up to 20 groups of start, stop
             and increment channel numbers plus IF numbers can be
             specified. The default (ICHANSEL = 0) is to average the
             center 75 percent of the band, i.e.
             ICHANSEL(1,1) = (# channels)/8 + 1
                       For example: # channels=16 => ICHANSEL(1,1)=3
             ICHANSEL(2,1) = (# channels + 1)*7/8
                       For example: # channels=16 => ICHANSEL(2,1)=14
             ICHANSEL(3,1) = 1
             ICHANSEL(4,1) = 0 (meaning all IFs).
             If ICHANSEL describes averaging explicitly for some IFs,
             but skips other IFs, then the center 75 percent of the band is
             averaged for the skipped IFs.  For example:
             ICHANSEL=2,6,1,2 => The channels 2-6 will be averaged for
             IF=2 and the center 75 percent of the band will be averaged for
             the rest of the IFs.
  DOFIT......Do opacity correction in APCAL.  This is recommended
             for high frequency experiments (freq >= 15~GHz) if the
             accuray of the source flux is important.
  BADDISK....A list of disks on which scratch files are not to
             be placed.  This will not affect the output file.

EXPLAIN SECTION

VLBAAMP:            Procedure to apply a-priori amplitude corrections
Documentor:         Amy Mioduszewski
Related Programs:   VLBAUTIL, ACSCL, SNSMO, APCAL, CLCAL

VLBAAMP determines the post-bandpass and delay calibration amplitude
correction and a-priori amplitude corrections from the gain curves and
system temperature measurements, and applies these corrections to the
highest numbered calibration (CL) table attached to the input file.
Note that interpolation type 'SELF' is used for the a-priori amplitude
calibration, to avoid interpolating between sources at different
elevations, among other things.

You should run VLBAAMP after loading any gain curves or system temperature
data for non-VLBA antennas using ANTAB.

VLBAAMP should be used along with (and after) VLBAACOR and VLBABPSS instead
of VLBACALA.  This redesign of the amplitude calibration path is based on
VLBA Scientific Memo #37 (Craig Walker).  VLBAAMP should NEVER be used with
VLBACALA.  The new recommended steps for amplitude calibration are:
  1) Do preliminary calibration steps that are necessary (e.g., VLBAFIX,
      VLBAEOPS, VLBATECR...).
  2) VLBACCOR -- digital sampling corrections
  3) VLBAMPCL (or VLBAPCOR) -- remove instrumental delay
  4) VLBABPSS -- do bandpass
  5) VLBAAMP -- correct auto-correlations and a priori amplitude calibration
  6) Continue with calibration.

ICHANSEL defaults to the inner 75 percent of each IF in ACSCL.  That is a good
deafult for the older PFB backend of the VLBA.  The inner 89 percent could be
used for the more modern DDC backend but this difference should not
matter much.  The more general advice would be to set it to the channels
you intend to use for imaging.


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