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Basic Information on mfclean


Task: mfclean
Purpose: Multi-frequency synthesis CLEAN.
Categories: deconvolution

        MFCLEAN is a MIRIAD task to deconvolve a multi-frequency
        synthesis image.  It can perform either Clark or Hogbom
        iterations.  To achieve good results, the width of the beam
        should be at least 3 times that of the region being cleaned.
        The region being cleaned should be reasonably centred in the
        map, and should have an appreciable guard band around it to the
        map edge (of size comparable to the width of the region being
        cleaned).
 
        To form a multi-frequency synthesis image and beam, use INVERTs
        "mfs" and "sdb" options.  This will create a map with one plane,
        and a beam with two planes (the normal dirty beam, and the
        spectral dirty beam).
 
        The result of MFCLEAN is a component image consisting of two
        planes.  The first plane contains the normal flux components.
        The second consists of components of "flux times spectral index"
        (that is, I*alpha).
 
        Use task MFSPIN to get a crude spectral index image from the
        output of MFCLEAN.
 
        The sign convention used for the spectral index, alpha, is that:
          I(f) = I(f0) * (f/f0) ** alpha
 
        MFCLEAN differs from CLEAN in a number of ways.
        * Task CLEAN only requires that the beam is twice the size of
          the region being cleaned whereas, for MFCLEAN, it is
          recommended that the dirty beam be three times the size of the
          region being cleaned.
        * MFCLEAN requires a guard band around the edge of the region
          being cleaned.
        * MFCLEAN does not have a Steer cleaning option, nor Prussian
          hats.

Key: map
        The input dirty map which should have units of Jy/beam.  No
        default.

Key: beam
        The input dirty beam. This should be formed using INVERT with
        options=sdb. No default.

Key: model
        An initial model of the deconvolved image.  This could be the
        output from a previous run of MFCLEAN.  It must have flux units
        of Jy/pixel.  The default is no model (i.e. a zero map).

Key: out
        The name of the output map.  The units of the output will be
        Jy/pixel.  This file will contain the contribution of the input
        model.  It will consist of two planes, giving the flux density
        image and the "flux times spectral index" image (also called the
        scaled flux derivative image).  No default.

Key: gain
        The minor iteration loop gain.  Two values can be given, the
        second being the gain for the spectral components.  If only one
        value is given, the flux and spectral components use the same
        gain.  The default is 0.1.

Key: cutoff
        MFCLEAN finishes when the absolute maximum residual falls below
        CUTOFF. Default is 0. When two values are given, do a deep
        clean to the second cutoff limiting peak finding to
        the pixels that are already in the model.

Key: niters
        The maximum number of minor iterations.  MFCLEAN finishes when
        abs(NITERS) minor iterations have been performed.  Clean may
        finish before this point, however, if NITERS is negative and the
        absolute maximum residual becomes negative valued, or if the
        cutoff level (as described above) is reached. Optional second
        value will force MFCLEAN to report on the level reached and
        (for mode=clark) start a new major iteration at least every
        niters(2) iterations. This can be useful to avoid overcleaning.

Key: region
        This specifies the region to be Cleaned.  See the User's Manual
        for instructions on how to specify this.  The default is
        generally inadequate, and a smaller region should be explicitly
        specified. An easy way to do this is using the percentage option
        of region. When the beam is the same size as the image use
        region=perc(33), for a 'double' size beam use region=perc(66).

Key: minpatch
        The minimum patch size when performing minor iterations.
        Default is 511, but make it larger if you are having problems
        with corrugations.  You can make it smaller when cleaning
        images that consist of a pretty good dirty beam.

Key: speed
        This is the same as the speed-up factor in the AIPS APCLN.
        Negative values makes the rule used to end a major iteration
        more conservative.  This causes less components to be found
        during a major iteration, and so should improve the quality of
        the Clean algorithm.  Usually this will not be needed unless you
        are having problems with corrugations.  A positive value can be
        useful when cleaning simple point-like sources.  Default is 0.

Key: mode
        This can be either "hogbom", "clark" or "any", and determines
        the Clean algorithm used.  If the mode is "any" MFCLEAN
        determines which is the best algorithm to use.  The default is
        "any".

Key: log
        Output log file containing a list of all the components.  The
        log file consists of 5 columns, being the iteration number, the
        x and y pixel coordinate (in the output model; this goes from 1
        to N), the "I" component and the "I*alpha" component.  The
        default is to not create a log file.
 
Revision: 1.14, 2017/10/19 04:45:13 UTC

Generated by miriad@atnf.csiro.au on 19 Oct 2017