Basic Information on linmos

Task: linmos
Purpose: Linear mosaicing of datacubes
Categories: map combination

        LINMOS is a MIRIAD task that performs simple linear mosaicing
        of input cubes to produce a single output cube.  If only one
        input cube is given, LINMOS essentially does primary beam
        correction on it.  If the input cubes overlap, LINMOS combines
        the overlapping regions so as to minimize the rms error.
 
        To determine the primary beam of the telescope, LINMOS first
        checks the map header for the presence of the "pbtype" and then
        "pbfwhm" parameters.  If present, LINMOS assumes the primary
        beam is the given type.  If these parameters are missing, LINMOS
        checks if the telescope is one that it knows.  If so, then the
        known form for the primary beam is used. See task "pbplot" to
        check LINMOS's primary beam models.

Key: in
        The names of the input cubes - many may be given.  There is no
        default.  Inputs should generally be on the same grid system,
        use invert with options=mosaic and the offset keyword to achieve
        this. If not, linear interpolation is performed to regrid using
        the first plane of the first image as the template. LINMOS's
        ability to do this is inferior to task REGRID.
        The intensity units of all the inputs, and the pixel size and
        alignment of the third dimension are assumed to be the same.
        Mosaicing fields with different resolution together will cause
        errors in the fluxdensities of sources.

Key: out
        The name of the output cube.  No default.  The center and pixel
        size of the first input image is used as the grid system of the
        output. The synthesized beam parameters are also taken from the
        first image header - you may want to pick a better average beam.

Key: rms
        RMS noise level in each of the input cubes.  If not specified,
        the value is taken from the 'rms' item in the input image header
        if that is available, and if not, then the rms of the previous
        image is used.  If no value could be determined for the first
        image, a warning is issued and ALL images are given equal weight
        by assigning an RMS of 1.0.

Key: bw
        Bandwidth of the image in GHz, default 0. If specified the beam
        response will either be averaged across the frequency band before
        being applied to the image or, if the input images contain a
        spectral index plane (created with the mfs option of restor)
        the images will be evaluated and corrected across the band.
        Use this for wide band images to improve the accuracy of the
        correction.
        Note that doing wide band primary beam correction at low
        frequency will make the effective observing frequency vary
        significantly across the field.
        An optional second parameter can be given to set the number
        of frequencies to divide the bandwidth into, it defaults to 10.
 

Key: cutoff
        The cutoff level to use for the primary beam, e.g., use 0.5 to
        restrict the contribution of each input cube to the pixels inside
        the half power beam width. Normally the built-in level for each
        beam model is used (generally <0.1). This can be useful
        e.g., to restrict polarization mosaics to use only the part of
        the beam with low instrumental polarization. Use pbplot to see
        what radius each level corresponds to. Defaults to zero
        which means use the built-in level.

Key: options
        Extra processing options.  Several can be given, separated by
        commas.  Minimum match is supported.  Possible values are:
          taper        By default, LINMOS fully corrects for primary
                       beam attenutation.  This can cause excessive
                       noise amplification at the edge of the mosaiced
                       field.  The `taper' option aims at achieving
                       approximately uniform noise across the image.
                       This prevents full primary beam correction at the
                       edge of the mosaic.  See Eq. (2) in Sault,
                       Staveley-Smith and Brouw (1996), A&AS, 120, 375,
                       or use "options=gains" to see the form of the
                       tapering.
          sensitivity  Rather than a mosaiced image, produce an image
                       giving the RMS noise across the field.  This is
                       dependent on the RMS specified, either as an
                       input parameter or else as a header item (see
                       above).
          gain         Rather than a mosaiced image, produce an image
                       giving the effective gain across the field.  If
                       options=taper is used, this will be a smooth
                       function.  Otherwise it will be 1 or 0 (blanked).
          frequency    Rather than a mosaiced image, produce an image
                       giving the effective frequency across the field.
          alpha        If an I*alpha plane is present in the input,
                       produce a mosaiced version of this as well.
                       You can feed the output image to mfspin to
                       produce the mosaiced spectral index image.
                       The spectral index mosaic becomes unreliable
                       when the fractional bandwidth is > 0.4 (this
                       is because higher orders are needed to model
                       the primary beam response with frequency).
 
Revision: 1.34, 2021/06/03 07:09:31 UTC