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Basic Information on mfclean
Purpose: Multi-frequency synthesis CLEAN.
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
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
* MFCLEAN does not have a Steer cleaning option, nor Prussian
The input dirty map which should have units of Jy/beam. No
The input dirty beam. This should be formed using INVERT with
options=sdb. No default.
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).
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.
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.
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.
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.
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).
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.
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.
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
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 email@example.com on 19 Oct 2017