UV_GAIN

        UV_GAIN

    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 antenna-based  method  takes  the  closure relationships  into   ac-
    count.  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  particu-
    lar, the  atmospheric phase contribution  must be stable on the scan du-
    ration.

    Similarly, the source structure should be small enough so that visibili-
    ties  take  during  the  averaging  time  represent the same measurement
    (within the Nyquist sampling). This can be ensured  to  first  order  by
    centering the image on the strongest source.