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Basic Information on pmosmem
Purpose: Maximum Entropy deconvolution for polarization mosaics
PMOSMEM is a MIRIAD task that performs a joint maximum entropy
deconvolution of polarized mosaiced images. Optionally it can
perform a joint deconvolution with a single dish image as well.
Two to five input images. The first must be a Stokes-I mosaic,
then one or more polarized mosaics (Stokes Q, U and V images),
and then optionally a Stokes-I single dish image. These should
have units of Jy/beam. The mosaics should be produced by
INVERT's mosaic mode. All the images must be on exactly the
same pixel grid. If necessary, use REGRID to make this so.
One or perhaps two input dirty beams. The first, corresponding
to the mosaics, 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.
The default image. This is the Stokes-I 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
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 PMOSMEM, as a model, to continue the
The maximum number of iterations. The default is 30.
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.
Tolerance of solution. There is no need to change this from the
default of 0.01.
One or two values (corresponding to the mosaic and single dish
observations). These give estimates of the number of points per
beam. PMOSMEM can usually come up with a good, image-dependent
PMOSMEM 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 PMOSMEM. This is easily done: for image
puthd in=xxxx/rms value=????
where "????" is the rms noise in Jy/beam.
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 that the single-dish data should be multiplied
by to convert it to the same flux units as the mosaic. The
default is 1.
An estimate of the integrated flux of the source. This
parameter cannot be used if there is an input single dish image.
Giving PMOSMEM 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 PMOSMEM will NOT constrain the integrated
flux to be this value, but see the "doflux" option below. The
default is image-dependent.
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
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
Revision: 1.7, 2016/03/18 03:25:44 UTC
Generated by firstname.lastname@example.org on 21 Jun 2016