casa6

<casaxml xsi:schemaLocation="http://casa.nrao.edu/schema/casa.xsd       file:///opt/casa/code/xmlcasa/xml/casa.xsd" xmlns="http://casa.nrao.edu/schema/psetTypes.html" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

​

<task type="function" name="initweights" category="calibration">

      <shortdescription>Initializes weight information in the MS</shortdescription>

​

<input>

      <param type="path" name="vis" mustexist="true"><shortdescription>Name of input visibility file (MS)</shortdescription><description>Name of input visibility file (MS)</description>

            <value/>

      </param>

      <param type="string" name="wtmode"><shortdescription>Initialization mode</shortdescription><description>Initialization mode</description>

            <value>nyq</value>

                <allowed kind="enum">

                       <value>nyq</value>

                       <value>sigma</value>

                       <value>weight</value>

                       <value>ones</value>

                       <value>delwtsp</value>

                       <value>delsigsp</value>

                       <value>tsys</value>

                       <value>tinttsys</value>

                </allowed>

      </param>

      <param type="path" name="tsystable" mustexist="false" subparam="true"><shortdescription>Tsys calibration table to apply on the fly</shortdescription><description>Tsys calibration table to apply on the fly</description>

            <value/>

      </param>

​

      <param type="string" name="gainfield" subparam="true"><shortdescription>Select a subset of calibrators from Tsys table</shortdescription><description>Select a subset of calibrators from Tsys table</description>

            <value/>

      </param>

​

      <param type="string" name="interp" subparam="true"><shortdescription>Interpolation type in time[,freq]. default==\'linear,linear\'</shortdescription><description>Interpolation type in time[,freq]. default==\'linear,linear\'</description>

            <value/>

      </param>

​

      <param type="intVec" name="spwmap" subparam="true"><shortdescription>Spectral windows combinations to form for gaintable(s)</shortdescription><description>Spectral windows combinations to form for gaintable(s)</description>

            <value/>

      </param>

​

      <param type="bool" name="dowtsp"><shortdescription>Initialize the WEIGHT_SPECTRUM column</shortdescription><description>Initialize the WEIGHT_SPECTRUM column</description>

            <value>False</value>

      </param>

​

   <constraints>

        <when param="wtmode">

                <equals value="nyq"/>

                <equals value="sigma"/>

                <equals value="weight"/>

                <equals value="ones"/>

                <equals value="delwtsp"/>

                <equals value="delsigsp"/>

                <equals value="tsys">

                        <default param="tsystable"><value type="string"/></default>

                        <default param="gainfield"><value type="string"/></default>

                        <default param="interp"><value type="string"/></default>

                        <default param="spwmap"><value type="intVec"/></default>

            </equals>

                <equals value="tinttsys">

                        <default param="tsystable"><value type="string"/></default>

                        <default param="gainfield"><value type="string"/></default>

                        <default param="interp"><value type="string"/></default>

                        <default param="spwmap"><value type="intVec"/></default>

            </equals>

        </when>

   </constraints>

      </input>

<returns type="void"/>

​

<example>

​

      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 per-spectral window 

      weight information should have been initialized properly at 

      fill time (v4.2.2 and later). To set per-channel weights, use 

      initweights(vis=finalvis,wtmode='weight',dowtsp=True)

​

      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 wtmode='weight', WEIGHT_SPECTRUM will be initialized according

      to the existing WEIGHT column; dowtspec=T must be specified in

      this case.

      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'),

      i.e.,

          tsys    : weight=bw/Tsys^2

          tinttsys: weight=bw*t_int/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

                channelized flag).

      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

      twice.

      !!! USERS ARE ADVISED 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

      development).

      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.

​

 </example>

 </task>

 </casaxml>