Specify Calibration Values of Various Types
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 applycal. Several
specialized calibrations are also generated with gencal.
Current antenna-based gencal options (caltype) are:
'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)
'antpos' = ITRF antenna position corrections
'antposvla' = VLA-centric antenna position corrections
'tsys' = Tsys from the SYSCAL table (ALMA)
'swpow' = EVLA switched-power gains (experimental)
'evlagain' (='swpow') (this syntax will deprecate)
'rq' = EVLA requantizer gains _only_
'swp/rq' = EVLA switched-power gains divided by requantizer gain
'opac' = Tropospheric opacity
'gc' = Gain curve (zenith-angle-dependent gain) (VLA only)
'eff' = Antenna efficiency (sqrt(K/Jy)) (VLA only)
'gceff' = Gain curve and efficiency (VLA only)
The calibration specifications are not time-variable in the
present implementation. Calibration values can be assigned to
each spw, antenna and pol selection, where applicable. The
same caltable can be specified for multipl runs of gencal,
in which case the specified parameters will be incorporated
cumulatively. E.g., amplitude parameters (caltype='amp')
multiply and phase-like parameters ('ph', 'sbd','mbd','antpos')
add. 'amp' and 'ph' parameters can be incorporated into the
same caltable (in separate 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 caltables are applied to the data by using applycal. Other
calibration tables must also be present, if applicable.
For antenna position corrections (caltype='antpos'), the antenna
position offsets are specified in the ITRF frame. For EVLA, 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 EVLA antenna position correction
site. If no corrections are found, it will throw an exception
with the message, "no offsets found. no caltable created". The task
may terminate with a SEVERE error message and may sound alarming, but
it simply means that it cannot produce the caltable.
For VLA position corrections in the VLA-centric frame, use
caltype='antposvla', and gencal will rotate them to ITRF before
storing them in the output caltable.
For Tsys (caltype='tsys', for ALMA) and EVLA switched power
corrections (caltype='swpow'), the calibration parameters are
derived from information contained in MS subtables. In these
cases, specification of spw, antenna, pol, and parameter will be
ignored.
EVLA switched power calibration is supported in three modes:
'swpow' (formerly 'evlagain', a syntax which will
deprecate) yields the formal EVLA 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 calculate normally).
The 'rq' and 'swp/rq' modes are are mainly intended for testing
and evaluating the EVLA switched power systems.
For caltype='opac', specify the desired opacity(ies) in the parameter
argument. At this time, 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. The parameter argument is
ignored. These caltypes are currently only supported
for VLA processing. (Appropriate factors for ALMA are TBD.)
Keyword arguments:
vis -- Name of input visibility file
default: none. example: vis='ngc5921.ms'
caltable -- Name of input/output caltable. If it does not
exist, it will be created. Specifying an
existing table will result in the parameters
being applied cumulatively. Only a single
time-stamp for all calibrations are supported,
currently. Do not use a caltable
created by gaincal, bandpass, etc.
default: none. example: caltable='test.G'
caltype -- The calibration parameter type being specified.
Options include:
'amp' = gain (G) amplitude (1 real parameter per
pol, antenna, spw)
'ph' = gain (G) phase (deg) (1 real parameter per
pol, antenna, spw)
'sbd' = single-band delays (nsec) (1 real parameter
per pol, antenna, spw)
'mbd' = multi-band delay (nsec) (1 real parameter
per pol, antenna, spw)
'antpos' = antenna position corrections (m) (3 real
ITRF offset parameters per antenna; spw, pol
selection will be ignored)
With antenna='', this triggers an automated lookup
of antenna positions for EVLA.
'antposvla' = antenna position corrections (m) specified
in the old VLA-centric coordinate system
'tsys' = Tsys from the SYSCAL table (ALMA)
'evlagain' = EVLA switched-power gains (experimental)
'opac' = Tropospheric opacity (1 real parameter
per antenna, spw)
'gc' = Antenna zenith-angle dependent gain curve (auto-lookup)
'gceff' = Gain curve and efficiency (auto-lookup)
'eff' = Antenna efficiency (auto-lookup)
default: none.
example: caltype='ph'
spw -- Spectral window selection for specified parameters.
default: spw='' (specified parameters apply to all spws)
example: spw = '2,3,4'
antenna -- Antenna selection for specified parameters.
default: antenna='' (specified parameters apply to all antennas)
example: antenna='ea02, ea03' (specified parameter(s) to
apply to ea02 and ea03 only)
pol -- Polarization selection for specified parameters.
default: pol='' (specified parameters apply to all polarizations)
example: pol='R' (specified parameters to apply to
R only)
parameter -- The calibration parameters, specified as a list, to
store in the caltable for the spw, antenna, and pol
selection. The required length of the list is
determined by the caltype and the spw, antenna, pol
selection. One "set" of parameters (e.g., one value
for 'amp', 'ph', etc., three values for 'antpos')
specified the same value for all indicated spw, antenna,
and pol.
OR,
When specifying a long list of calibration parameter 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 must not be
enumerated in the parameter list
Examples:
gencal(vis='test.ms',caltable='test.G',caltype='amp',
spw='',antenna='',pol='',
parameter=[3])
--> 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 than is (1/3*1/3) less than the
uncorrected visibility.
gencal(vis='test.ms',caltable='test.G',caltype='ph',
spw='',antenna='ea03,ea04',pol='',
parameter=[45,120])
--> 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='ea05,ea06',pol='R',
parameter=[63,-34])
--> Gain phase corrections for antennas ea05 and ea06
will be adjusted (additive) by 63 and -34
degrees (respectively), in R only, for all spws
gencal(vis='test.ms',caltable='test.G',caltype='ph',
spw='',antenna='ea09,ea10',pol='R,L',
parameter=[14,-23,-130,145])
--> 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.
gencal(vis='test.ms',caltable='test.G',caltype='ph',
spw='2,3',antenna='ea09,ea10',pol='',
parameter=[14,-23,-130,145])
--> 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.
gencal(vis='test.ms',caltable='test.G',caltype='sbd',
spw='2,3',antenna='ea09,ea10',pol='',
parameter=[14,-23,-130,145])
--> 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.
gencal(vis='test.ms',caltable='test.G',caltype='antpos',antenna='')
--> *** Currently EVLA observations only ***
Antenna position corrections will be retrieved automatically
over internet to generate the caltable with antenna=''.
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 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='antposvla',
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.
1.8.0