gencal(vis, caltable='', caltype='', infile='', spw='', antenna='', pol='', parameter='', uniform=True)¶
Specify Calibration Values of Various Types
vis (path) - Name of input visibility file
caltable (string=’’) - Name of input calibration table
caltype (string=’’) - The calibration type: (amp, ph, sbd, mbd, antpos, antposvla, tsys, evlagain, opac, gc, gceff, eff, tecim)
spw (string=’’) - Select spectral window/channels
antenna (string=’’) - Select data based on antenna/baseline
pol (string=’’) - Calibration polarizations(s) selection
parameter (doubleVec=’’) - The calibration values
The gencal task provides a means of specifying antenna-based calibration values manually. The values are put in designated tables and applied to the data using other tasks (applycal, gaincal, bandpass, etc.). Several specialized calibrations are also generated with gencal.
Calibration types: caltype
The gencal task supports many different calibration types via the caltype parameter. These are listed here in two groups. Many of these options are part of Preparing for Calibration and more information about how they work can be found in that section.
The following enable directly specifying calibration factors for each specified pol, antenna, spw. Except where noted, each expects one real parameter value per specified pol, antenna, and spw.
‘amp’= amplitude correction
‘ph’ = phase correction
‘sbd’= single-band delay (phase-frequency slope for each spw)
‘mbd’= multi-band delay (phase-frequency slope over all spw)
‘opac’ = Tropospheric opacity (1 real parameter [in nepers] per antenna, spw)
‘antpos’ = ITRF antenna position corrections (3 real parameters [in m] for each antenna; see below)
‘antposvla’ = VLA-centric antenna position corrections (3 real parameters [in m] for each antenna; see below)
The following caltype options automatically generate caltables from ancilliary information found in the MS or elsewhere. The pol, antenna, spw, and parameter options are ignored for these.
‘tsys’ = Tsys from the MS.SYSCAL table (ALMA, VLBI)
‘swpow’ = VLA switched-power gains from MS.SYSPOWER, CALDEVICE
‘rq’ = VLA requantizer gains _only_
‘swp/rq’ = VLA switched-power gains divided by requantizer gain
‘gc’ = Gain curve (zenith-angle-dependent gain) (VLA, VLBI)
‘eff’ = Antenna efficiency (sqrt(K/Jy)) (VLA only)
‘gceff’ = Gain curve and efficiency (VLA only)
‘tecim’ = Time-dependent TEC image specified in infile subparameter
‘antpos’ = For VLA datasets, automatic lookup of antenna position corrections if antenna=’’
For the VLA, caltype=’gc’ will do auto-lookup the gain curve information. For VLBI, gain curve information will be taken from MS.GAIN_CURVE when present or from an external table specified by the infile subparameter.
Specifying calibration values: pol, antenna, spw, parameter
Generic calibration values for the “manual caltype s” listed above should be specified in the parameter argument as a list. The length of the list must correspond to the net length of the specific polarizations, antennas, and spws specified in the pol, antenna, and spw selection arguments. The values specified in parameter will be duplicated over all members of any selection axis that is not explicitly specified (pol =’’, spw =’’ and/or antenna =’’) E.g., if pol = antenna = spw =’’, it only makes sense to specify a single parameter value (or three, for antpos and antposvla), and this will be duplicated for all pols, antennas, and spws. If multiple parameter values are specified, at least one of pol, spw, or antenna must be non-trivial, and the number of values in parameter must be consistent with the range of specified pol, spw, and/or antenna. E.g., if only a non-trivial spw selection is specified, then the parameter value list should match the number of spws specified, and these values will be duplicated for all polarizations and antennas. If more than one of pol, spw, and antenna is non-trivially specified, the number of parameter * values specified should match the product of the number specified selection elements. The *parameter values should be sorted by pol (fastest), antenna, and spw (slowest). Un-specified elements on non-trivially specified axes will be filled with nominal values (i.e., it is not necessary to exhaustively specify all elements on any axis or use nominal parameter values explicitly). Please consult the examples for additional guidance. There is currently no support for time-dependent calibration specfication; in all cases, the specified parameter values will be assumed constant in time (though their impact on the data may be time-dependent, depending on the caltype).
The same caltable can be specified for multiple runs of gencal, in which case the specified parameter values will be incorporated cumulatively. E.g., amplitude-like values (caltype=’amp’) multiply and phase-like values (‘ph’, ‘sbd’,’mbd’,’antpos’) add. Also, ‘amp’ and ‘ph’ calibrations can be incorporated into the same caltable (in separate cumulative runs), but each of the other types require their own unique caltable. A mechanism for specifying manual corrections via a text file will be provided in the future.
The calibration tables generated by gencal can be applied to the data in all other tasks that accept specified calibration for (pre-)application, e.g., applycal. gaincal, bandpass, etc.
Consult the Examples for more information on the many caltype options in gencal.
Notes on specific caltype s
‘antpos’ For antenna position corrections (caltype=’antpos’), the antenna position offsets are specified in the ITRF frame. For the Karl G. Jansky VLA, automated lookup of the antenna position corrections is enabled when antenna is unspecified (antenna=’’) for this caltype. Note that this requires internet connection to access the VLA antenna position correction site.
‘antposvla’ For (old) pre-upgrade VLA position corrections, specify the values in the VLA-centric frame and gencal will rotate them to ITRF before storing them in the output caltable.
VLA switched power calibration is supported in three modes: ‘swpow’ (formerly ‘evlagain’, a syntax which has been deprecated) yields the formal VLA switched power calibration which describes voltage gain as sqrt(Pdif/Tcal) (used to correct the visibility data) and Tsys as Psum*Tcal/Pdif/2 (used to correct the weights). ‘swpow’ implicitly includes any requantizer gain scale and adjustments. ‘rq’ yields only the requantizer voltage gains (Tsys is set to 1.0 to avoid weight adjustments). ‘swp/rq’ yields the ordinary switched power voltage gains divided by the requantizer voltage gain (Tsys is calculated normally). The ‘rq’ and ‘swp/rq’ modes are are mainly intended for testing and evaluating the VLA switched power systems.
For caltype=’opac’, only constant (in time) opacities are supported via gencal.
For gaincurve and efficiency (caltype=’gc’, ‘gceff’, or ‘eff’), observatory-provided factors are determined per spw according to the observing frequencies. These caltypes are currently only supported for VLA (including pre-upgrade VLA) and VLBI processing. (Appropriate factors for ALMA are TBD.)
In the following example, antenna-based gain amplitude corrections for all spws, antennas, and polarizations will be multiplied by 3. When applied to visibility data, this correction will produce a corrected visibility that is (1/3*1/3) less than the uncorrected visibility.
In the following example, gain phase corrections for antennas ea03 and ea04 will be adjusted (additive) by 45 and 120 degrees (respectively), for all spws and polarizations. When these phases are applied to visibility data, the visibility phases will decrease or increase by the specified amount where the selected antennas occur first or second (respectively) in each baseline. E.g., the phase of baseline ea03&ea04 will change by (-45+120) = + 75 degrees. Baseline ea01&ea03’s phase will change by +45 degrees; baseline ea04&ea05’s phase will change by -120 degrees. The same phase sign convention is used for delay and antenna position corrections.
gencal(vis='test.ms',caltable='test.G',caltype='ph', spw='',antenna='ea03,ea04',pol='', parameter=[45,120])
Gain phase corrections for antennas ea05 and ea06 will be adjusted (additive) by 63 and -34 degrees (respectively), in R only, for all spws
Gain phase corrections in all spws will be adjusted for antenna ea09 by 14 deg in R and -23 deg in L, and for antenna ea10 by -130 deg in R and 145 deg in L.
Gain phases corrections in both polarizations will be adjusted for antenna ea09 by 14 deg in spw 2 and -23 deg in spw 3, and for antenna ea10 by -130 deg in spw 2 and 145 deg in spw 3.
Delay corrections in both polarizations will be adjusted for antenna ea09 by 14 nsec in spw 2 and -23 nsec in spw 3, and for antenna ea10 by -130 nsec in spw 2 and 145 nsec in spw 3. See the above example for caltype=’ph’ for details of the sign convention adopted when applying delay corrections.
Currently Karl G. Jansky VLA observations only Antenna position corrections will be retrieved automatically over internet to generate the caltable with antenna=’’.
Antenna position corrections in meters (in ITRF) for antenna ea09 (dBx=0.01, dBy=0.02, dBz=0.03) and for antenna ea10 (dBx=-0.03, dBy=-0.01, dBz=-0.02). See the above example for caltype=’ph’ for details of the sign convention adopted when applying ‘antpos’ corrections.
gencal(vis='test.ms',caltable='test.G',caltype='antpos',antenna='ea09,ea10', parameter=[0.01,0.02,0.03, -0.03,-0.01,-0.02])
Antenna position corrections (in the traditional VLA-centric frame) will be introduced in meters for antenna ea09 (dBx=0.01, dBy=0.02, dBz=0.03) and for antenna ea10 (dBx=-0.03, dBy=-0.01, dBz=-0.02). These offsets will be rotated to the ITRF frame before storing them in the caltable. See the above example for caltype=’ph’ for details of the sign convention adopted when applying antpos corrections.
gencal(vis='test.ms',caltable='test.G',caltype='antposvla',antenna='ea09,ea10', parameter=[0.01,0.02,0.03, -0.03,-0.01,-0.02])
No additional development details
- Parameter Details
Detailed descriptions of each function parameter
vis (path)- Name of input visibility fileDefault: noneExample: vis=’ngc5921.ms’
caltable (string='')- Name of input calibration tableDefault: noneIf a calibration table does not exist, it will becreated. Specifying an existing table will resultin the parameters being appliedcumulatively. Only a single time-stamp for allcalibrations are supported, currently. Do notuse a caltable created by gaincal, bandpass,etc.Example: caltable=’test.G’
caltype (string='')- The calibration parameter type being specifiedDefault: noneOptions: ‘amp’, ‘ph’, ‘sbd’, ‘mbd’, ‘antpos’,‘antposvla’, ‘tsys’, ‘evlagain’, ‘opac’, ‘gc’,‘gceff’, ‘eff’, ‘tecim’* ‘amp’ = gain (G) amplitude (1 real parameterper pol, antenna, spw)* ‘ph’ = gain (G) phase (deg) (1 real parameterper pol, antenna, spw)* ‘sbd’ = single-band delays (nsec) (1 realparameter per pol, antenna, spw)* ‘mbd’ = multi-band delay (nsec) (1 realparameter per pol, antenna, spw)* ‘antpos’ = antenna position corrections (m) (3real ITRF offset parameters per antenna; spw,pol selection will be ignored)With antenna=’’, this triggers an automatedlookup of antenna positions for EVLA and ALMA.* ‘antposvla’ = antenna position corrections (m)specified in the old VLA-centric coordinatesystem* ‘tsys’ = Tsys from the SYSCAL table (ALMA)* ‘evlagain’ = EVLA switched-power gains(experimental)* ‘opac’ = Tropospheric opacity (1 real parameterper antenna, spw)* ‘gc’ = Antenna zenith-angle dependent gaincurve (auto-lookup)* ‘gceff’ = Gain curve and efficiency(auto-lookup)* ‘eff’ = Antenna efficiency (auto-lookup)Example: caltype=’ph’
infile (string='')- Input ancilliary fileSubparameter of caltype=’gc|gceff|tecim’Default: none
spw (string='')- Select spectral window/channelsDefault: ‘’ (all spectral windows and channels)Examples:spw=’0~2,4’; spectral windows 0,1,2,4 (all channels)spw=’<2’; spectral windows less than 2 (i.e. 0,1)spw=’0:5~61’; spw 0, channels 5 to 61spw=’0,10,3:3~45’; spw 0,10 all channels, spw3 - chans 3 to 45.spw=’0~2:2~6’; spw 0,1,2 with channels 2through 6 in each.spw = ‘*:3~64’ channels 3 through 64 for all sp id’sspw = ‘ :3~64’ will NOT work.
antenna (string='')- Select data based on antenna/baselineSubparameter of selectdata=TrueDefault: ‘’ (all)If antenna string is a non-negative integer, itis assumed an antenna index, otherwise, it isassumed as an antenna nameExamples:antenna=’5&6’; baseline between antennaindex 5 and index 6.antenna=’VA05&VA06’; baseline between VLAantenna 5 and 6.antenna=’5&6;7&8’; baselines withindices 5-6 and 7-8antenna=’5’; all baselines with antenna index5antenna=’05’; all baselines with antennanumber 05 (VLA old name)antenna=’5,6,10’; all baselines with antennas5,6,10 index numbers
pol (string='')- Polarization selection for specified parametersDefault: pol=’’ (specified parameters apply toall polarizations)Example: pol=’R’ (specified parameters toapply to R only)
parameter (doubleVec='')- The calibration valuesThe calibration parameters, specified as a list,to store in the caltable for the spw, antenna,and pol selection. The required length of thelist is determined by the caltype and the spw,antenna, pol selection. One “set” of parameters(e.g., one value for ‘amp’, ‘ph’, etc., threevalues for ‘antpos’) specified the same value forall indicated spw, antenna, and pol.OR,When specifying a long list of calibrationparameter values, these should be ordered first(fastest) by pol (if pol!=’’), then by antenna(if antenna!=’’), and finally (sloweset) by spw(if spw!=’’). Unspecified selection axes mustnot be enumerated in the parameter list
uniform (bool=True)- Assume uniform calibration values across the arraySubparameter of caltype=’tsys’Default: TrueOptions: True|False