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mfclean

Section: User Commands (1)
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NAME

mfclean - Multi-frequency synthesis CLEAN.  

PERSON RESPONSIBLE

rjs  

CATEGORIES

deconvolution  

DESCRIPTION

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 is the normal flux components. The second plane are 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.  

PARAMETERS

map
The input dirty map, which should have units of Jy/beam. No default.
beam
The input dirty beam. This should be formed using INVERT with options=sdb. No default.
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).
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.
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.
cutoff
MFCLEAN finishes when the absolute maximum residual falls below CUTOFF. Default is 0.
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.
region
This specifies the region to be Cleaned. See the Users Manual for instructions on how to specify this. The default is generally inadequate, and a smaller region should be explicitly specified.
minpatch
The minimum patch size when performing minor iterations. Default is 51, but make this larger if you are having problems with corrugations. You can make it smaller when cleaning images which consist of a pretty good dirty beam.
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.
mode
This can be either "hogbom", "clark" or "any", and determines the Clean algorithm used. If the mode is "any", then MFCLEAN determines which is the best algorithm to use. The default is "any".
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.


 

Index

NAME
PERSON RESPONSIBLE
CATEGORIES
DESCRIPTION
PARAMETERS

This document was created by man2html, using the manual pages.
Time: 18:35:38 GMT, July 05, 2011