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Initializes weight information in the MS
Name of input visibility file (MS)
Tsys calibration table to apply on the fly
Select a subset of calibrators from Tsys table
Interpolation type in time[,freq]. default==linear,linear
Spectral windows combinations to form for gaintables(s)
Initialize the WEIGHT_SPECTRUM column.
This task provides for initialization of the weight information
in the MS. For ALMA interferometry and EVLA data, it should not
generally be necessary to use this task, as the weight information
should have been initialized properly at fill time (v4.2.2 and later).
Several initialization modes are supported via the wtmode parameter.
If wtmode=’nyq’ (the default), SIGMA and WEIGHT will be
initialized according to bandwidth and integration time. This
is the theoretically correct mode for raw normalized visibilities.
(e.g., ALMA). For the EVLA, this is correct if switched-power
and bandpass calibration will later be applied.
If wtmode=’sigma’, WEIGHT will be initialized according to the
existing SIGMA column.
If mode=’weight’, WEIGHT_SPECTRUM will be initialized according
to the existing WEIGHT column; dowtspec=T must be specified in
If wtmode=’ones’, SIGMA and WEIGHT will be initialized with 1.0,
globally. This is a traditional means of initializing weight
information, and is adequate when the integration time and
bandwidth are uniform. It is not recommended for modern
instruments (ALMA, EVLA), where variety in observational setups
is common, and properly initialized and calibrated weights
will be used for imaging sensitivity estimates.
There are two EXPERIMENTAL modes, wtmode=’tsys’ and ’tinttsys’.
In the modes, SIGMA and WEIGHT will be initialized according to
Tsys, bandwidth, and integration time (used only in ’tinttsys’),
tsys : weight=bw/Tsys^2
These modes use Tsys values to calculate weight as is done in
Tsys calibration. Tsys values are taken from a tsys calibration
table given as tsystable. Selection of gain field (gainfield),
interpolation method (interp), and spectral window mapping (spwmap)
are supported, too.
Available types of interpolation are,
Time: ’nearest’, ’linear’, the variation of those with ’perobs’,
e.g., ’linearperobs’ (enforce obsId boundaries in interpolation)
Freq: ’nearest’, ’linear’, ’cubic’, ’spline’, and the variation
of those with ’flag’, e.g., ’linearflag’ (with
See the help of applycal for details of interpolations.
Note if the weight in an MS is initialized with these modes and
Tsys calibration table is applied with calwt=True after that, the
weight would be contaminated by being devided by square of Tsys
!!! USERS ARE ADVICED TO USE THESE EXPERIMENTAL MODES WITH CARE !!!
For the above wtmodes, if dowtsp=T (or if the WEIGHT_SPECTRUM
column already exists), the WEIGHT_SPECTRUM column will be
initialized (uniformly in channel in wtmode=’nyq’, ’sigma’,
’weight’, and ’ones’), in a manner consistent with the
disposition of the WEIGHT column. If the WEIGHT_SPECTRUM
column does not exist, dowtsp=T will force its creation.
Use of the WEIGHT_SPECTRUM column is only meaningful
for ALMA data which will be calibrated with channelized
Tsys information, or if the weights will become channelized
after calibration, e.g., via averaging over time- and
channel-dependent flagging. (A task for channel-dependent
weight estimation from the data itself is also currently under
In non-channelized modes (wtmode=’nyq’, ’sigma’, ’weight’, and
’ones’) or when dowtsp=F, SIGMA_SPECTRUM column will be removed
from MS. On the other hand, SIGMA_SPECTRUM column is added and
initialized in channelized modes (wtmode=’tsys’ and ’tinttsys’)
if dowtsp=T or WEIGHT_SPECTRUM already column exists.
Two additional modes are available for managing the spectral
weight info columns; these should be used with extreme care: If
wtmode=’delwtsp’, the WEIGHT_SPECTRUM column will be deleted (if
it exists). If wtmode=’delsigsp’, the SIGMA_SPECTRUM column
will be deleted (if it exists). Note that creation of
SIGMA_SPECTRUM is not supported via this method.
Note that this task does not support any prior selection.
Intialization of the weight information must currently be done
globally or not at all. This is to maintain consistency.
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