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Basic Information on clean
Purpose: Apply Hogbom, Clark or Steer CLEAN algorithm to a map
CLEAN is a MIRIAD task that performs a hybrid Hogbom/Clark/Steer
Clean algorithm, which takes a dirty map and beam, and produces
an output map which consists of the Clean components. This
output can be input to SELFCAL to self-calibrate visibilities,
or input to RESTOR to produce a "clean" image. Optionally CLEAN
can take as one of its inputs a model of the deconvolved image.
This model could be from a previous CLEAN run, or from other
deconvolution tasks (e.g. MAXEN).
The input dirty map, which should have units of Jy/beam. No
The input dirty beam. No default
An initial model of the deconvolved image. This could be the
output from a previous run of CLEAN, or the output of any of the
deconvolution tasks (e.g. MAXEN). 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 also should have a different name to the input model
(if any). It can be input to RESTOR, CLEAN (as a model, to do
more cleaning), or SELFCAL (for self-calibrating visibility
The minor iteration loop gain. Default is 0.1.
Extra processing options. Several can be given, separated
by commas. Minimum match is used. Possible values are:
negstop Stop when the first negative component is
encounterd. This does not apply when using Steer
positive Apply a positivity constraint. This constrains the
component image to be non-negative. A side-effect
of this is that CLEAN will stop iterating if it
cannot continue to ensure this. This does not apply
when using Steer iterations.
asym The beam is asymmetric. By default CLEAN assumes
the beam has a 180 degree rotation symmetry, which
is the norm for beams in radio-astronomy.
pad Double the beam size by padding it with zeros. This
will give you better stability with Clark and Steer
modes if you are daring enough to CLEAN an area more
than half the size (in each dimension) of the dirty
CLEAN finishes either when the absolute maximum residual falls
below CUTOFF, or when the criteria described below is
satisfied. The default CUTOFF is 0.
The maximum number of minor iterations. The default is 250,
which is too small for all but the simplest of images. CLEAN
will stop when either the maximum number of iterations is
performed, or the cutoff (see above) is reached, or if
options=negstop was given and a negative component was found,
or if options=positive was given, and no more positive
components could be found.
This specifies the region to be Cleaned. See the help on
region for more information. The default is the largest
region that can be deconvolved safely.
Cornwell's Prussian helmet parameter. When cleaning extended
sources, CLEAN may produce a badly corrugated image. This can
be suppressed to some extent by cleaning with a dirty beam which
has had a spike added at its center (i.e. a beam that looks like
a Prussian helmet). PHAT gives the value of this spike, with 0
to 0.5 being good values. Default is 0 (but use a non-zero
value for extended sources).
The minimum patch size when performing minor iterations, in
pixels. 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.
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 fewer 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", "steer" or "any", and
determines the Clean algorithm used. If the mode is "any", then
CLEAN determines which is the best algorithm to use. The default
This sets the relative clip level in Steer mode. Values are
typically 0.75 to 0.9. The default is image dependent.
Revision: 1.14, 2015/10/29 01:31:02 UTC
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