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clean

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NAME

clean - Apply Hogbom, Clark or Steer CLEAN algorithm to a map  

PERSON RESPONSIBLE

rjs  

CATEGORIES

deconvolution  

DESCRIPTION

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).  

PARAMETERS

map
The input dirty map, which should have units of Jy/beam. No default.
beam
The input dirty beam. No default
model
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).
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 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 data).
gain
The minor iteration loop gain. Default is 0.1.
options
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
            iterations.
  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
            beam.
cutoff
CLEAN finishes either when the absolute maximum residual falls below CUTOFF, or when the criteria described below is satisfied. The default CUTOFF is 0.
niters
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.
region
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.
phat
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).
minpatch
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.
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 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.
mode
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 is "any".
clip
This sets the relative clip level in Steer mode. Values are typically 0.75 to 0.9. The default is image dependent.

ean.for,v 1.6 2011/06/28 01:43:17 pteuben Exp $


 

Index

NAME
PERSON RESPONSIBLE
CATEGORIES
DESCRIPTION
PARAMETERS

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