Content-type: text/html Manpage of pmosmem


Section: User Commands (1)
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pmosmem - Maximum Entropy deconvolution for polarization mosaics  






PMOSMEM is a MIRIAD task which 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 c Stokes-I single dish image. These should have units of Jy/beam. The mosaics should be produced by INVERTs 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 correct flux.
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 deconvolution process.
The maximum number of iterations. The default is 30.
This specifies the region to be deconvolved. See the Users 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 estimate.
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 xxxx, use

  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 which 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
             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.




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Time: 18:35:38 GMT, July 05, 2011