AIPS NRAO AIPS HELP file for REWEIGHT in 31DEC21



As of Thu Dec 2 18:21:15 2021



HELP SECTION

REWEIGHT
Type: Adverb (Real(2))

Use: All uv data have associated weights which express the
     relative value of the data.  Internally, these weights are
     treated as statistical weights (i.e. 1 / variance
     (amplitude)).  These weights are used in making images but
     are modified by uniform weighting and tapering.  In
     practice, the weights coming into AIPS from non-AIPS
     calibration systems are in arbitrary units so a
     renormalization of the weights may be necessary when data
     sets are combined.

     The adverb REWEIGHT can be used to modify the relative
     weights of the two input data sets.  The simplest way to
     determine the appropriate relative weighting is to image each
     set of data independently in the same fashion as the desired
     final image (i.e. using the same IMSIZE, CELLSIZE, UVWTFN,
     UVBOX, and UVTAPER but not necessarily doing a deconvolution).
     All AIPS imaging tasks report the "sum of the gridding weights"
     in the message file.  This is the sum of the weights after all
     corrections are applied (this value has been written into the
     history file since 15JUL89).  REWEIGHT is a pair of values to be
     multiplied by the input weights for the first (1) and second (2)
     input uv data file.  These values should be set such that the
     two data sets will have the desired relative sum of weights.

     For example, if the two data sets before DBCON give a sum
     of gridding weights of 1.0E5 and 2.0E2 when imaged by IMAGR AND
     you wish to make them contribute equally to the final image then
     use: REWEIGHT = 1.0,1.0e5/2.0e2 (or 1, 500).

     REWEIGHT is also used by a variety of tasks for various
     re-weighting purposes.

Null value: 0 will be interpreted as 1.0

Tasks:
  BSGEO...Beam-switched Az-El image to RA-Dec image translation
          REWEIGHT(2) minimum convolved weight.
  BSGRD...Task to image beam-switched single-dish data
          REWEIGHT type output, min convolved weight
  DBCON   Used to concatenate 2 uv data sets.  REWEIGHT described
          above in detail.
  DSKEW...Geometric interpolation correction for skew
          REWEIGHT interpolation halfwidth, min fraction good pixels
  FLATN...Re-grid multiple fields into one image incl sensitivity
          REWEIGHT interpolation halfwidth, min fraction good pixels
  OGEOM...Simple image rotation, scaling, and translation
          REWEIGHT interpolation halfwidth, min fraction good pixels
  OHGEO...Geometric interpolation with correction for 3-D effects
          REWEIGHT interpolation halfwidth, min fraction good pixels
  SDGRD...Task to select and image random-position single-dish data
          REWEIGHT type output, min convolved weight
  SDIMG...Task to select and image random-position single-dish data
          REWEIGHT type output, min convolved weight
  SYSOL...Undoes and re-does nominal sensitivity application for Solar
          data   REWEIGHT does additional scaling of visibilities,
          weights.
  TVIEW...Display image cube in all 3 transpositions with rotation &
          reference.  REWEIGHT interpolation halfwidth, min fraction
          good pixels
  TYAPL...Undoes and re-does nominal sensitivity application
          REWEIGHT does additional scaling of visibilities, weights.

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