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UV_SINGLE

        UV_SINGLE

    CAUTION: This task is obsolete. It is keeped because it is still used by
    the ALMA simulator.

    This task prepares one or more (for mosaics) UV tables of short spacings
    from  a   single-dish  table  of  spectra  (as produced by CLASS command
    GRID).  This table may later be merged to an  interferometer  UV  table.
    Two major steps are performed for this:
      - Creation of a "well behaved" map from the spectra.
      - Extraction of UV spacings from this map.

    The  "well  behaved" map is obtained by linear operations (convolutions)
    from the original spectra, in an optimum way from signal to noise  point
    of  view.  The map is extrapolated smoothly towards zero at the map edge
    in order to avoid further aliasing in the Fourier  transform  operations
    required  in  step 2. This extrapolation has a scale length of twice the
    single-dish beam, in order to avoid spurious Fourier components.

    To obtain it, UV_SINGLE performs the following operations:
      -  Resampling (in space) of the original spectra on a regular grid  by
        convolution  with  a  small  (typically 1/4 of the single-dish beam)
        gaussian convolving kernel. In this process, the weights of individ-
        ual spectra is carried on a weight map.
      -  Extrapolation by zero outside the convex hull of the mapped region
      -   Convolution  of the result by a gaussian twice as wide as the sin-
        gle-dish beam.
      -  Within the convex hull of the mapped region, the  smoothed  map  is
        replaced by the original map.

    From this map, UV_SINGLE computes one or several UV tables (one for each
    pointing center in case of a mosaic) in the following way:
      -  Fourier transform of the single dish map
      -  Division by the Fourier transform of the single dish  beam,  up  to
        a maximum spacing (SD_DIAM$, in meters)
      -  Inverse Fourier transform to  the  image  plane
    and then for each pointing center
      -   Multiplication of the  image  by the primary beam of the interfer-
        ometer elements
      -  Fourier transform back to the UV plane.
      -  Creation of the UV table, with a given weight SD_WEIGTH$ and an ap-
        propriate calibration factor to Janskys SD_FACTOR$

    Both the single-dish and the interferometer antennas are assumed to have
    gaussian beams (SD_BEAM$ and IP_BEAM$, in radians).


Gildas manager 2011-09-07