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Basic Information on uvmodel
Purpose: Add, subtract, etc, a model from a uv data set.
Categories: uv analysis
UVMODEL is a MIRIAD task that modifies a visibility dataset by
combining or replacing it a model. Allowed operations are
adding, subtracting, multiplying, dividing and replacing. The
model is specified in the image domain, so that its Fourier
transform is first computed before application to the
visibilities. The model may be either an image (e.g., a CLEAN
component image) or a point source.
As an example, UVMODEL could be used to remove CLEAN components
from a visibility data file. The residual data base could then
be examined for anomalous points, which could in turn be
clipped. UVMODEL could then be reapplied to add the CLEAN
components back into the visibility data base for re-imaging.
Input visibility data file. No default
Input model cube. The default is a point source model. This
will generally be a deconvolved map formed from the visibility
data being modified. It should be made with "channel" linetype.
The model should have units of JY/PIXEL and be weighted by the
primary beam. The task DEMOS can be used to extract primary
beam weighted models from a mosaiced image.
The standard uv selection subcommands. The default is all data.
This gives extra processing options. Several values can be
given though many are mutually exclusive, separated by commas.
Option values can be abbreviated to uniqueness.
Possible options are (no default):
add Form: out = vis + model
subtract Form: out = vis - model
multiply Form: out = vis * model
divide Form: out = vis / model
replace Form: out = model
flag Form: out = vis, but flag data where the difference
between vis and model is greater than "sigma"
unflag Unflag any flagged data in the output.
mosaic Select only those visibilities whose observing
centre is within plus or minus three pixels of the
model reference pixel. This is needed if there are
multiple pointings or multiple sources in the input
uv file. By default no observing centre selection
mfs This is used if there is a single plane in the input
model, which is assumed to represent the data at all
frequencies. This should also be used if the model
has been derived using MFCLEAN.
zero Use zero as the value of the model if it cannot be
calculated. This can be used to avoid flagging the
data in the outer parts of the u-v-plane when
subtracting a low resolution model.
The operations add, subtract, multiply, divide, replace and flag
are mutually exclusive. The operations flag and unflag are also
The unflag option should be used with caution. Data in the
output may still be flagged, if it was not possible to calculate
Clip level. Pixels in the model below this level are set to
zero. The default is not to perform any clipping.
If MODEL is blank, then the flux (Jy) of a point source model
should be specified here. Also used as the default flux in the
apriori option. The default is 1 (assuming the model parameter
is not given). The flux can optionally be followed by i,q,u,v
or the other polarisation mnemonics to indicate the polarisation
type. The 3rd-6th parameter optionally specify the reference
frequency in GHZ and the spectral index and higher order terms
(as given by uvsfit or uvfmeas with options=mfflux).
The RA and DEC offsets (arcsec) of the point source from the
observing centre. A point source to the north and east has
positive offsets. Defaults are zero.
The visibility linetype to use, in the standard form, viz:
Generally if there is an input model, this defaults to the
linetype parameters used to construct the map. For a point
source or planet model, the default is all channels. This
parameter may be used if you wish to override these defaults,
or if the relevant information is not present in the header,
For options=flag, UVMODEL flags those points in the output that
differ by more than "sigma" sigmas. The default is 100.
Output visibility data file name. The output file will contain
only as many channels as there are planes in the model cube.
The various uv variables that describe the windows are adjusted
accordingly. No default.
Revision: 1.12, 2021/06/03 07:09:31 UTC
Generated by email@example.com on 03 Jun 2021