When the model contains multiple planes, it should be noted that the
tasks do not perform any interpolation of models along the spectral
The self-calibration tasks assume that there is a one-to-one correspondence
between a model plane and some average of the channels. The
correspondence is determined in a rather imperfect fashion - the
self-calibration tasks use the
standard line parameter (see Section 5.4).
This parameter determines the channels selected from the visibility
dataset, and the averaging performed on them. Unfortunately, the
self-calibration tasks only perform rudimentary checks on whether the
line parameter makes sense (i.e. whether the selected channels
have the same frequencies as the model planes). Despite this, in
many instances, the self-calibration tasks will provide appropriate defaults
for the line parameter.
Below we outline those instances where you can or should
allow the line parameter to default, and those instances where you
- Miriad tasks normally maintain a record of the line
parameter used to form an image. The imaging task, invert,
records the line parameter it uses, and the deconvolution tasks
propagate it to their outputs. The default line parameter used by
the self-calibration tasks is that which was used to form the model.
This is generally quite appropriate if the model was formed from the
data being self-calibrated. However if the model was formed by some
other means, then the default will be quite inappropriate, and you
should set the line parameter explicitly.
can cope with the case of several models being
derived from different channel ranges from one visibility dataset.
This might occur, for example, if multiple lines were being observed
simultaneously (as often happens at millimeter wavelengths, but rarely
with the ATCA). In this case, the different models were formed with
different line parameters. selfcal
must rely on the
record of the line parameter stored in the model.
- If a point-source model is used (i.e. no input model dataset),
then you should give the line parameter explicitly.
- Similarly, if using the
mfs option, you should also
set the line parameter explicitly - see the next subsection.