AIPS HELP file for DIGICOR in 31DEC26

As of Tue Feb 10 14:02:07 2026

HELP SECTION

DIGICOR
Type: Adverb  (Logical,  > 0  =>  true)
Use:  Standard data selection adverb. True (1) means apply
      the digital corrections to VLBA data in FITLD.
      False (-1,0) means do not apply the corrections.
Null value:  false (-1)
Tasks:
   FITLD.........Reads FITS files to load images or UV (IDI or UVFITS)
                 data to disk.  DIGICOR use for IDI only: Data processed
                 in digital correlators such as the VLBA correlator and
                 DiFX are affected by a variety of phenomena that we
                 collectively refer to as digital effects. FITLD is able
                 to apply the corrections needed to scale the data to
                 the values that would be returned by a purely analogue
                 correlator.  DIGICOR = -1 will turn off the application
                 of these correction, DIGICOR = 0 or 1 will apply them
                 to both cross and total power, DIGICOR = 2 will apply
                 the corrections to cross-power and only to total power
                 if zero-padding was used in the correlator.  The latter
                 case is designed to deal with a situation in which the
                 total-power spectrum is dominated by multiple, strong
                 spectral lines.  In that case, if zero-padding was not
                 used, the reconstructed total-power spectrum, after an
                 FFT, is inaccurate at some level. In all continuum
                 cases DIGICOR = 1 should be the default.  In nearly all
                 line cases DIGICOR = 1 is fine. only if the Tant in the
                 line is about equal to the Tsys should DIGICOR = 2 be
                 used.  One word of caution, for data correlated prior
                 to Aug 1 1994 the correlator was incorrectly scaling
                 the data by a factor of 1.57 (i.e. PI/2) . So for that
                 data, DIGICOR can be used but a BFACTOR of 0.6369 (i.e.
                 1/1.57) should be applied in APCAL or to the final
                 images.  Unfortunately FITLD had no knowledge of the
                 date of correlation so cannot perform this correction.
                 The code detects data from the DiFX correlator and
                 applies a different (1.0) saturation correction in that
                 case.
            **** FITLD no longer alters DIGICOR for non-VLBA arrays,
            **** so set it carefully.  Before 5 Feb 2013, it changed
            **** DIGICICOR to -1 if the array name was not VLBA.
            **** Note that DiFX correlators may write VLBA as the
            **** array even when no VLBA antennas are involved.

EXPLAIN SECTION