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Basic Information on uvdiff
Task: uvdiff
Purpose: Difference two visibility datasets.
Categories: uv analysis
Given two Miriad visibility datasets, UVDIFF matches and
optionally subtracts one from the other. In doing this, UVDIFF
assumes that the two datasets sample the same source using the
same array configuration and observing frequency setup (no
checks are made to verify these). UVDIFF matches visibility
records based on baseline number, polarisation type and hour
angle. If the hour angles in the two datasets do not match to
better than 1 second, UVDIFF linearly interpolates between two
integrations of one dataset to the appropriate hour angle of the
other.
NOTE: UVDIFF does not apply calibration corrections to either
of the input datasets. The datasets should be in time order.
Key: vis
The two datasets to difference. No default. When differencing,
the output is the first minus the second. The first visibility
dataset is used as the template for the output. It is the
second dataset that is interpolated when needed.
Key: select
Standard visibility selection keyword. See the help on select
for more information. Note that this selection is applied ONLY
to the first visibility dataset. The default is to select
everything.
Key: out
The output dataset. No default.
Key: mode
This determines what data is written. Possible values are:
difference Write the difference of the two inputs (the first
minus the second). This is the default.
two Write the data from the second input, interpolated
to the first.
one Write the first dataset.
With the exception of the visibility data itself, all three
possibilities will produce identical datasets. This includes
identical flagging information.
Any of these modes can be prefixed with a minus sign. In this
case the output visibilities are negated.
Key: tol
Interpolation tolerance, in minutes. This gives the maximum gap
between two integrations to interpolate across. The default is
2 minutes.