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Basic Information on mosmem


Task: mosmem
Purpose: Maximum Entropy deconvolution for a mosaiced image
Categories: deconvolution

        MOSMEM is a MIRIAD task that performs a maximum entropy
        deconvolution of a mosaiced image.  Optionally it can also
        perform a joint deconvolution of a mosaic and single dish image.
 
        MOSMEM will also work correctly on a single-pointing observation
        interferometric observation.  In this case, it will be less
        efficient than MAXEN, but it could be used when combining single
        dish data with a single pointing.
 
        MOSMEM spits out some information as it goes:
 
        RMSFAC is the ratio (actual rms)/(theoretical rms).  It measures
        the residuals (i.e. the difference between the dirty image and
        the model modified by the point spread function).  RMSFAC should
        converge to 1.
 
        NormGrd is normalised gradient in the maximisation process.
        Convergence requires this to be less than 0.05
 
        Flux is the sum of all the pixel values in the model.
 

Key: map
        One or perhaps two input dirty images (or cubes).  These should
        have units of Jy/beam.  The first should be produced by INVERTs
        mosaic mode.  The optional second dirty map can be a single-dish
        image.  It must be on exactly the same pixel grid as the first
        image.  If necessary, use REGRID to make this so.  If two inputs
        are given, then a joint deconvolution of the two is performed.

Key: beam
        One or perhaps two input dirty beams.  The first, corresponding
        to the first input dirty map, will be produced by INVERTs mosaic
        mode.  There is no default.  The second dirty beam (which must
        be given if there are two dirty map inputs) gives the point-
        spread function of the single dish dirty map.  This second dirty
        beam need not be the same image size as the input dirty maps,
        and may be appreciably smaller.  This single-dish beam is
        assumed to be position-independent, but it need not be
        symmetric.

Key: model
        An initial estimate of the deconvolved image.  For point
        sources, giving a good initial model may help convergence.  In
        principle, this only helps convergence, but should not affect
        the final solution.  The model could be the output from a
        previous run of MOSMEM or any other deconvolution task.  It must
        have flux units of Jy/pixel.  The default is a flat estimate,
        with the correct flux.

Key: default
        The default image.  This is the image that the final solution
        will tend towards.  The final result will be influenced by this
        default if the constrains that the data put on the solution are
        weak.  The default is a flat estimate, with the correct flux.

Key: out
        The name of the output map.  The units of the output will be
        Jy/pixel.  It can be input to RESTOR to produce a restored
        image, or alternatively to MOSMEM, as a model, to continue the
        deconvolution process.

Key: niters
        The maximum number of iterations.  The default is 30.

Key: region
        This specifies the region to be deconvolved.  See the User's
        Manual for instructions on how to specify this.  The default is
        the entire image.

Key: measure
        The entropy measure to be used, either "gull" (-p*log(p/e)) or
        "cornwell" (-log(cosh(p)) -- also called the maximum emptiness
        criteria).  Using the maximum emptiness criteria is not
        recommended.

Key: tol
        Tolerance of solution.  There is no need to change this from the
        default of 0.01.

Key: q
        One or two values (corresponding to the mosaic and single dish
        observations).  These give estimates of the number of points per
        beam.  MOSMEM can usually come up with a good, image-dependent
        estimate.

Key: rmsfac
        MOSMEM must be able to the theoretical rms noise of the input
        dirty map(s), and will, by default, attempt to reduce the
        residuals to have the same rms as this.  If the true rms noise
        is different from the theoretical, you may give the factor to
        multiply by to convert from theoretical to true rms noise.
 
        The theoretical rms will usually be an optimistic estimate of
        the true noise level.  The true noise will be increased by
        calibration errors, confusion, poorly understood distant
        sidelobes, etc.  The rmsfac factor gives some "fudge factor"
        (usually greater than 1) to scale the theoretical noise estimate
        by.  Either one or two values can be given, with the second
        value corresponding to the single dish input.
 
        For a mosaic, the theoretical rms is position dependent, and is
        determined from information save by INVERT (the mostable table).
        For a single dish image, the rms is assumed to be constant
        across the field, and given by the "rms" item in the image.  If
        the single dish input does not contain this item, then this must
        be added before using MOSMEM.  This is easily done: for image
        xxxx, use
          puthd in=xxxx/rms value=????
        where "????" is the rms noise in Jy/beam.

Key: factor
        The flux calibration factor.  This is only relevant when doing a
        joint deconvolution of a mosaic and a single-dish image.  It
        gives the factor which the single-dish data should be multiplied
        by to convert it to the same flux units as the mosaic.  The
        default is 1.  If the "dofactor" options is used (see below),
        MOSMEM solves for this parameter.

Key: flux
        An estimate of the integrated flux of the source.  This
        parameter is generally not useful if there is an input single
        dish image.  Giving MOSMEM a good value for the integrated flux
        will help it find a good solution.  On the other hand, giving a
        poor value may do harm.  Normally MOSMEM will NOT constrain the
        integrated flux to be this value, but see the "doflux" option
        below.  The default is image-dependent for measure=gull, and
        zero for measure=cornwell.  A value can be given for each plane
        being deconvolved.

Key: options
        Task enrichment parameters.  Several can be given, separated by
        commas.  Minimum match is used.  Possible values are:
          doflux     Constrain the solution to have the correct
                     integrated flux (normally the integrated flux is
                     not constrained).  The integrated flux is
                     determined from the "flux" parameter or (if no flux
                     parameter is given) from the default image.  This
                     option cannot be used if a single dish input map is
                     also given.
          dofactor   Solve for the flux calibration factor.
          verbose    Give lots of messages during the iterations.  The
                     default is to give a one line message at each
                     iteration.
 
Revision: 1.8, 2016/07/14 02:15:13 UTC

Generated by miriad@atnf.csiro.au on 14 Jul 2016