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    UV_GAIN  computes a table of phase and/or amplitude gains from the self-
    calibration of an observed UV table on a model UV table.  The  table  of
    self-calibrated visibilities is also output.  The table of gain can then
    be applied to another UV table through the UV_CAL task. This  is  useful
    for instance to calibrate a line UV table from reference to the gain de-
    rived from the self-calibration of the high signal-to-noise  ratio  con-
    tinuum  UV table of the same source. Only one channel of the observed UV
    table can be calibrated at a time.

    It is STRONGLY ADVISED to self-calibrate the phase first, then  the  am-
    plitude  using a longer smoothing time. You can choose between baseline-
    based and antenna-based method to determine the gain.

      - The baseline-based method output self-calibrated visibilities which are
        identical to the modeled visibilities.  This means that your model must
        be correct to avoid bias.
      - On  the  other  hand,   the  antenna-based  method  takes  the  closure
        relationships into  account. You may thus  iterate the self-calibration
        using this method to try to converge. However, for this method to work,
        decorrelation on  the duration of each  observed scan must  be small to
        avoid  the   loss  of  the  amplitude  closure   relationships  in  the
        averaging. In  particular, the  atmospheric phase contribution  must be
        stable on the scan duration.

Gildas manager 2014-07-01