Documentation on uvflux

Task: uvflux
Purpose: Determine some statistics about visibilities.
Categories: uv-analysis

        UvFlux is a MIRIAD task which gives a mean visibility value.
        The visibilities are averaged together regardless of time, (u,v)
        coordinate, frequency or baseline. Distinct polarisations
        and sources, however, are averaged separately. This task will be
        most useful when examining the fluxes of point sources.

        Both vector and scalar averages are formed. It also prints out
        the rms scatter around the vector mean, and the RMS variation
        in the amplitude.

        Definitions in Detail: UvFlux prints out five quantities.

        Theoretical RMS -- This is the rms error, resulting from
        receiver thermal noise, that would be expected in the real or
        imaginary part of each visibility.

        Vector Average -- This is simply the normal average (mean)
        of the real and imaginary parts of the visibility data (although it
        is printed out in amplitude and phase form). For a point source,
        the amplitude should give the point source flux density, and the
        phase should be zero (or perhaps 180 degrees, for Stokes Q,U,V).

        RMS Scatter -- This is the RMS scatter of real and imaginary
        parts of the actual visibilities around their mean value. If the
        data do represent a point source, and it is well calibrated, this
        should be the same number as the ``Theoretical RMS''.

        Average Amplitude -- This gives the mean value of the visibilty
        amplitude (the so-call amplitude scalar average). If the S/N
        ratio is much less than 1, this average amplitude will be dominated
        by thermal noise bias, and should be 1.25 times larger than the
        ``Theoretical RMS''. If the S/N ratio is much greater than 1, then
        this should be a good estimate of the point-source's flux density.
        This will be unaffected by phase calibration errors (unlike the
        ``Vector Average'', which decorrelates).

        RMS Amp Scatter -- This gives the RMS scsatter of the visibility
        amplitudes around the mean visibility amplitude. If the S/N ratio
        is much less than 1, then this should be 0.65 times the ``Theoretical
        RMS'. If the S/N ratio is much greater than 1, this should be the
        same as ``Theoretical RMS''.

        Number Visibs -- This gives the number of visibilities, N, used in
        forming each mean. NOTE that the three RMS values printed are RMS
        difference between the visibilities and some mean -- it is not
        an error-of-the-mean. To convert an RMS to an error-in-the-mean,
        divide by sqrt(N).

Key: vis
        The name of the input visibility data-set. Several files can be
        given, wildcarding is supported. No default.

Key: select
        Standard uv selection. The default is all data.

Key: line
        Standard line-type specification. When there are multiple channels
        selected, uvflux averages them all together.

Key: stokes
        Normal Stokes processing. You can select several Stokes or
        polarisation parameters, which will be be averaged independently.

Key: offset
        An offset (arcsec) to shift the uv data. The sign convention is the
        same as INVERT, MAXFIT, UVFIT, etc. The default is 0,0 (no shift).

Key: options
        Extra processing options. Several can be given, separated by
        commas. Minimum match is used. Possible values are:
          nocal    Do not apply any antenna gain calibration corrections.
                   By default these are applied if they exist.
          nopol    Do not apply polarisation leakage corrections. By default
                   these are applied if they exist.
          nopass   Do not apply bandpass corrections. By default these
                   are applied if they exist.