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Basic Information on offaxis
Task: offaxis
Purpose: Remove (or simulate) ATCA off-axis instrumental polarisation.
Categories: uv analysis
OFFAXIS is a Miriad task which attempts to remove off-axis
instrumental polarisation from ATCA observations. As input,
OFFAXIS takes a visibility dataset and a model of the source
total intensity (Stokes I). Given this, it computes the expected
off-axis effects (given its internal models of the effects),
subtracts this from the data, and produces an output (nominally)
corrected dataset.
Key: vis
Input visibility dataset. No default.
Key: select
Normal visibility selection parameter. The default is to
select all data. See the help on select for more information.
Key: line
Normal line parameter with the normal defaults. See the help on
line for more information.
Key: stokes
Stokes/polarisations to be processed. The default is XX,YY,XY,YX.
The only other legitimate value is I.
Key: model
Input model of the total intensity image. No default. This should
be the apparent total intensity (i.e. not corrected for primary
beam attenuation) in Jy/pixel
Key: out
The name of the output, corrected, visibility dataset. No default.
Key: clip
Pixels in the model less (in absolute value) than the clip level
are treated as if they are 0. The default is 0.
Key: options
Task enrichment parameters. Several can be given, separated by
commas. Only the minimum number of characters to guarantee
uniqueness are needed. Possible options are:
replace Normally OFFAXIS subtracts the computed off-axis
response from the data. This option causes the
visibility to be replaced with the model.
nocal Do not apply any antenna gain calibration. The default
is to apply these if they are available.
nopol Do not apply any polarization leakage correction. The
default is to apply these if they are available.
nopass Do not apply bandpass calibration. The default is to
apply these calibrations if they are available.