UV_PREVIEW Algorithm

###
UV_PREVIEW Algorithm

            UV_PREVIEW  computes  for  Ntapers different tapers the spectrum to-
        wards the phase center. The taper ranges are determined from the  avail-
        able  baseline  lengths  and telescope diameter. Ntapes is controlled by
        the value of Key TAPER.

        These spectra are then smoothed by averaging  several  channels  (1,4,16
        and 64) to be sensitive to different linewdiths. The nummber of smoothed
        spectra per taper is controlled by the value of Key SMOOTH.

        For each spectrum, UV_PREVIEW then attempts to figure out  if  there  is
        line  emission and the line-free channels to define the continuum level.
        This is based on the histogram of  the  intensity  distribution  of  all
        channels. The most likely value and the noise level is derived from this
        histogram. An iterative scheme, blanking out of range  (presumably  line
        emission) channels, is used for this to converge towards a Gaussian his-
        togram, which normally represents the noise distribution around the con-
        tinuum level.

        As  a last step, blanked channels are accumulated in a list of channels,
        which thus contain possible line emission at any of the Ntapers  angular
        scales and Nsmooth spectral resolutions.