1 UV_GAIN Compute (from self‐calibration of observation on a given model) a table of gain for use by UV_CAL
        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 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.

2 UVDATA$
        TASK\CHARACTER  "UV data table"         UVDATA$

    Input UV table to be self‐calibrated. This table can be a  continuum  or
    line table.

2 UVMODEL$
        TASK\CHARACTER  "UV model table"        UVMODEL$

    Input  UV  table of the source model. This table is assumed to have only
    one channel.

2 UVGAIN$
        TASK\CHARACTER  "UV gain table"         UVGAIN$

    Output table of gain for use by UV_CAL task. This table is will have on‐
    ly one channel.

2 UVCAL$
        TASK\CHARACTER  "UV calibrated table"   UVCAL$

    Output UV table of self‐calibrated visibilities.

2 TINTEG$
        TASK\REAL       "Smoothing time [s]"    TINTEG$

    Visibilities  of the input table will be averaged on TINTEG$ time inter‐
    vals to improve signal to noise ratio before self‐calibration.   Indeed,
    signal to noise MUST BE SUFFICIENT TO IMPROVE the phase or amplitude de‐
    terminations.  If TINTEG$ is too short, noise will be added to the data,
    rather than the expected improvement.  Required values are

            S/N    =  11  for 5 degree phase noise
            S/N    =  20  for 5 % amplitude correction

2 CHANNEL$
        TASK\INTEGER    "The channel number of input UV data"   CHANNEL$

    If  the  UV  table  (UVDATA$)  is a spectral line UV table, WCOL$ is the
    spectral channel to be self‐calibrated.

2 DO_AMP$
        TASK\LOGICAL    "Calibrate amplitudes"  DO_AMP$

    Logical switch to enable separate self‐calibration of amplitude. The ta‐
    ble of gain will then be filled only with the modulus of the gains.

2 DO_PHA$
        TASK\LOGICAL    "Calibrate phases"      DO_PHA$

    Logical  switch to enable separate self‐calibration of phases. The table
    of gain will then be filled only with the phase of the gains.

2 ANTENNA_BASED$
        TASK\LOGICAL    "Antenna based"         ANTENNA_BASED$

    Logical switch to compute the gains either by baseline or by antenna.

1 ENDOFHELP














































