AIPS HELP file for CALIB in 31DEC13
As of Mon May 20 14:49:56 2013
CALIB: Task to determine calibration for data.
Input uv data.
INNAME UV file name (name)
INCLASS UV file name (class)
INSEQ 0.0 9999.0 UV file name (seq. #)
INDISK 0.0 9.0 UV file disk drive #
Data selection (multisource):
CALSOUR Calibrator sources
QUAL -10.0 Calibrator qualifier -1=>all
CALCODE Calibrator code ' '=>all
SELBAND Bandwidth to select (kHz)
SELFREQ Frequency to select (MHz)
FREQID Freq. ID to select.
TIMERANG Time range to use.
ICHANSEL Array of start and stop chn
numbers, plus a channel
increment and IF to be used
for channel selection in the
averaging. See HELP ICHANSEL.
Default = center 75 percent of band.
ANTENNAS Antennas to select. 0=all
DOFIT Subset of ANTENNAS list for
which solns are desired.
ANTUSE Mean gain is calculated
(CPARM(2)>0) using only the
listed antennas. See explain.
SUBARRAY 0.0 1000.0 Subarray, 0=>all
UVRANGE Range of uv distance for full
WTUV Weight outside UVRANGE 0=0.
WEIGHTIT 0.0 3.0 Modify data weights function
Cal. info for input:
DOCALIB -1.0 101.0 > 0 calibrate data & weights
> 99 do NOT calibrate weights
NOT for single-source files
GAINUSE CL table to apply.
DOPOL -1.0 10.0 If >0 correct polarization.
PDVER PD table to apply (DOPOL>0)
BLVER BL table to apply.
FLAGVER Flag table version
DOBAND -1.0 10.0 If >0 apply bandpass cal.
Method used depends on value
of DOBAND (see HELP file).
BPVER Bandpass table version
SMOOTH Smoothing function. See
HELP SMOOTH for details.
CLEAN map. See HELP.
IN2NAME Cleaned map name (name)
IN2CLASS Cleaned map name (class)
IN2SEQ 0.0 9999.0 Cleaned map name (seq. #)
IN2DISK 0.0 9.0 Cleaned map disk unit #
INVERS -1.0 46655.0 CC file version #.
NCOMP # comps to use for model.
1 value per field
FLUX Lowest CC component used.
NMAPS 0.0 4096.0 No. Clean map files
CMETHOD Modeling method:
CMODEL Model type: 'COMP','IMAG'
'SUBI' (see HELP re images)
SMODEL Source model, 1=flux,2=x,3=y
See HELP SMODEL for models.
Output uv data file.
OUTNAME UV file name (name)
OUTCLASS UV file name (class)
OUTSEQ -1.0 9999.0 UV file name (seq. #)
OUTDISK 0.0 9.0 UV file disk drive #
DOAPPLY -1.0 1.0 >= 0 write output if
Solution control adverbs:
REFANT Reference antenna
SOLINT Solution interval (min)
SOLSUB Solution subinterval
SOLMIN Min solution interval
APARM General parameters
1=min. no. antennas
2 > 0 => data divided
3 > 0 => avg. RR,LL
5 > 0 => avg. IFs.
6=print level, 1=good,
2 closure, 3 SNR
7=SNR cutoff (0=>5)
8=max. ant. # (no AN)
9 > 0 => pass failed soln
10 < 99 cal output weights
DOFLAG Flag on closure error?
SOLTYPE Soln type,' ','L1','GCON',
'R', 'L1R', 'GCOR'
SOLMODE Soln. mode: 'A&P','P','P!A',
SOLCON Gain constraint factor.
MINAMPER 0.0 Amplitude closure error
regarded as excessive in percent
MINPHSER 0.0 Phase closure error regarded
as excessive in degrees
NORMALIZ -1.0 4.0 >0 => normalize gain:
1 globally, 2 by subarray,
3 by subarray,IF
4 by subarray,IF,pol
CPARM Phase-amp. parameters
1 = Min el for gain
2 > 0 normalize w median
else use mean
3 avg. amp. closure err
4 avg. ph. closure err
5 = 1 vector average
channels, scalar avg
>= 2 scalar average
6 limit clipping in robust
7 limit display of closure
SNVER -1.0 46655.0 Output SN table, 0=>new table
ANTWT Ant. weights (0=>1.0)
GAINERR Std. Dev. of antenna gains.
BADDISK Disk no. not to use for
Task: This task determines the calibration to be applied to a uv data
set given a model of the source(s). A solution (SN) table will
be written and attached to the INPUT uv file. If the input is
a single-source data set, an output data set may be written but
only if DOAPPLY >= 0.
Solutions are stored in solution (SN) tables. For
multi-source data, any previously unapplied SN tables can be
smoothed and applied to the specified CL table (multi-source data
only). This calibration (CL) table can be applied to the data
before determining the new calibration constants.
Model images made with both values of IMAGR's DO3DIMAG
option are handled correctly, as are multi-scale images. Set
NMAPS = NFIELD * NGAUSS.
CALIB now uses the "V polarization" flux when calibrating RR
(= I + V) and LL (= I - V) correlators. This may be used for
instruments with circular polarization if the calibrator is
circularly polarized (not usually significant). It may also be
used with equatorially mounted instruments having linearly
polarized feeds. Such feeds do not rotate with parallactic
angle and so have XX = I-Q and YY = I+Q. To calibrate these
instruments, relabel the Stokes from (-5 to -8) to (-1 to -4)
and put minus the Q flux into the V position (ZEROSP(4) in
SETJY). See note in EXPLAIN.
Models Of the basic flux calibrators 3C138, 3C147, 3C286, and
3C48 are provided with AIPS. These model images may be listed
with verb CALDIR and read in for use by CALIB with task CALRD.
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 -> highest.
INDISK.....Disk drive # of input UV file. 0 -> any.
The following are used for multisource data files only:
CALSOUR....List of sources for which calibration constants are to be
determined, i.e. the calibrator sources. All ' ' = all
sources; a "-" before a source name means all except ANY
source named. You must specify one and only one CALSOUR
if you want to apply a model using IN2NAME and IN2CLASS
to a multi-source file. Otherwise, for such files, the
program will quit if both IN2NAME and IN2CLASS are
specified. Note: solutions for multiple sources can only
be made if the sources are point sources at their assumed
phase center and with the flux densities given in the
source (SU) table.
QUAL.......Only sources with a source qualifier number in the SU
table matching QUAL will be used if QUAL is not -1.
CALCODE....Calibrators may be selected on the basis of the
' ' => any calibrator code selected
'* ' => any non blank code (cal. only)
'-CAL' => blank codes only (no calibrators)
anything else = calibrator code to select.
NB: The CALCODE test is applied in addition to the
other tests, i.e. CALSOUR and QUAL, in the
selection of sources for which to determine
SELBAND....Bandwidth of data to be selected. If more than one IF is
present SELBAND is the width of the first IF required.
Units = kHz, 0=> all
SELFREQ....Frequency of data to be selected. If more than one IF is
present SELFREQ is the frequency of the first IF
required. Units = MHz, 0=> all
FREQID.....Frequency identifier to select (you may determine which
is applicable from the OPTYPE='SCAN' listing produced by
LISTR. If either SELBAND or SELFREQ are set their values
override that of FREQID, however setting SELBAND and
SELFREQ may result in an ambiguity, in which case the
task will request that you use FREQID.
The following may be used for all data files (except as noted):
TIMERANG...Time range of the data to be used. In order:
Start day, hour, min. sec,
end day, hour, min. sec. Days relative to ref.
ICHANSEL...Array of start and stop channels plus a channel increment
and IF, used to select the channels to be averaged. For
instance, if you wished to exclude channels 1 - 10 and
121 - 128 because of bandpass effects, and channels 56 -
80 of IF 1 but not IF 2 because of interference, then you
would set ICHANSEL = 11,55,1,1, 81,121,1,1, 11,121,1,2.
If you only wished to use every other channel from the
second IF then you would set ICHANSEL = 11,55,1,1,
81,121,1,1, 11,121,2,2. Up to 20 groups of start, stop
and increment channel numbers plus IF numbers can be
specified. The default (ICHANSEL = 0) is to average the
center 75 percent of the band, i.e.
ICHANSEL(1,1) = (# channels)/8 + 1
For example: # channels=16 => ICHANSEL(1,1)=3
ICHANSEL(2,1) = (# channels + 1)*7/8
For example: # channels=16 => ICHANSEL(2,1)=14
ICHANSEL(3,1) = 1
ICHANSEL(4,1) = 0 (meaning all IFs).
If ICHANSEL describes averaging explicitly for some IFs,
but skips other IFs, then the center 75 percent of the band is
averaged for the skipped IFs. For example:
ICHANSEL=2,6,1,2 => The channels 2-6 will be averaged for
IF=2 and the center 75 percent of the band will be averaged for
the rest of the IFs.
ANTENNAS...A list of the antennas to have solutions
determined. If any number is negative then all
antennas listed are NOT to be used to determine
solutions and all others are. All 0 => use all.
DOFIT......A list of the antennas for which solutions should be
determined. Only those antennas listed in DOFIT will be
solved for; all data selected via ANTENNAS will be used to
form the solutions. If any antenna number in DOFIT is
<= -1, then DOFIT is taken as the list of antennas for
which no solution is desired; a solution is found for all
antennas not in DOFIT. Note that the REFANT, if specified,
will _not_ be solved for even if it appears in the DOFIT
list. Selection via DOFIT can be disabled by setting DOFIT
= 0 which defaults to solving for all antennas.
NOTE: THIS OPTION MUST NOT BE USED UNLESS YOU UNDERSTAND
IT FULLY. Basically, it should be used to solve for the
gains of "poor" antennas after the "good" antennas have
been fully calibrated. Antennas included in ANTENNAS but
not in DOFIT are assumed to have a complex gain of (1,0)
and the gains produced will be very wrong if this is not
the case. See HELP DOFIT.
ANTUSE.....A list of the antennas to be used in the calculation of
the mean gain modulus (NORMALIZ>0). If any number is
negative then all antennas listed are NOT to be used
to determine the gain normalization and all others are.
All 0 => use all. It can be useful to limit the
antennas used for the gain normalization to those with
good a priori calibration, especially when using
VLBI-style calibration based on system temperatures
and gains. This prevents the flux scale from being
dragged up or down by poorly calibrated antennas
including antennas subjected to bad weather. The
normalization factor determined using the ANTUSE
antennas is applied to all antennas.
SUBARRAY...Subarray number to use. 0=>all.
UVRANGE....The range of uv distance from the origin in
kilowavelengths over which the data will have
full weight; outside of this annulus in the uv
plane the data will be down weighted by a factor
WTUV.......The weighting factor for data outside of the uv
range defined by UVRANGE.
WEIGHTIT...If > 0, change the data weights by a function of the
weights just before doing the solution. Choices are:
0 - no change weighting by 1/sigma**2
1 - sqrt (wt) weighting by 1/sigma may be more stable
2 - (wt)**0.25
3 - change all weights to 1.0
DOCALIB....If true (>0), calibrate the data using information in the
specified Cal (CL) table for multi-source data. Also
calibrate the weights unless DOCALIB > 99 (use this for
old non-physical weights). Applied before determining
new solutions. Note that this make an unworkable
situation for single-source files (two SN tables which
cannot be combined), so DOCALIB is forced to false for
GAINUSE....Version number of the CL table to apply to the data.
0 => highest.
DOPOL......If > 0 then correct data for instrumental polarization as
represented in the AN or PD table. This correction is
only useful if PCAL has been run or feed polarization
parameters have been otherwise obtained. See HELP DOPOL
for available correction modes: 1 is normal, 2 and 3 are
for VLBI. 1-3 use a PD table if available; 6, 7, 8 are
the same but use the AN (continuum solution) even if a PD
table is present.
PDVER......PD table to apply if PCAL was run with SPECTRAL true and
0 < DOPOL < 6. <= 0 => highest.
BLVER......Version number of the baseline based calibration
(BL) table to apply. <0 => apply no BL table,
0 => highest.
FLAGVER....Specifies the version of the flagging table to be
applied. 0 => highest numbered table. <0 => no flagging
to be applied.
DOBAND.....(multi-source) If true (>0) then correct the data for the
shape of the antenna bandpasses using the BP table
specified by BPVER. The correction has five modes:
(a) if DOBAND=1 all entries for an antenna in the table
are averaged together before correcting the data.
(b) if DOBAND=2 the entry nearest in time (including
solution weights) is used to correct the data.
(c) if DOBAND=3 the table entries are interpolated in
time (using solution weights) and the data are then
(d) if DOBAND=4 the entry nearest in time (ignoring
solution weights) is used to correct the data.
(e) if DOBAND=5 the table entries are interpolated in
time (ignoring solution weights) and the data are then
BPVER......(multi-source) version of the BP table to be
applied. 0 => highest.
< 0 => no bandpass correction to be applied.
SMOOTH.....Specifies the type of spectral smoothing to be applied to
a uv database . The default is not to apply any smoothing.
The elements of SMOOTH are as follows:
SMOOTH(1) = type of smoothing to apply: 0 => no smoothing
To smooth before applying bandpass calibration
1 => Hanning, 2 => Gaussian, 3 => Boxcar, 4 => Sinc
To smooth after applying bandpass calibration
5 => Hanning, 6 => Gaussian, 7 => Boxcar, 8 => Sinc
SMOOTH(2) = the "diameter" of the function, i.e. width
between first nulls of Hanning triangle and sinc
function, FWHM of Gaussian, width of Boxcar. Defaults
(if < 0.1) are 4, 2, 2 and 3 channels for SMOOTH(1) =
1 - 4 and 5 - 8, resp.
SMOOTH(3) = the diameter over which the convolving
function has value - in channels. Defaults: 1,3,1,4
times SMOOTH(2) used when input SMOOTH(3) < net
The following specify a CLEAN model to be used if a single source was
specified in CALSOUR for multi-source files, or if the data is a
single-source file. Note that standard calibrator models are listed
by verb CALDIR and read in by task CALRD.
IN2NAME....Cleaned map name (name). ' ' => not Clean model.
For a single-source file the model determined by SMODEL
is used instead of the CLEAN components if IN2NAME = ' '
or IN2CLASS = ' '. For a multi-source file a point
source with flux given in the SU table is used instead of
a CLEAN components if IN2NAME = ' ' or IN2CLASS = ' '.
Note: a CLEAN image for only a single source may be given
although it may be in a multi-source file. One and only
one CALSOUR must be specified as well to apply a
Clean-component model to a source in a multi-source file
(even if the file actually contains only one source).
For a multi-source file, the flux of the clean components
selected for the model are summed and scaled to the source
flux found in the SU table. If that flux is zero, no
scaling is done.
IN2CLASS...Cleaned map name (class). ' ' => not Clean model.
IN2SEQ.....Cleaned map name (seq. #). 0 -> highest.
IN2DISK....Disk drive # of cleaned map. 0 => any.
INVERS.....CC file version #. 0=> highest numbered version
NCOMP......Number of Clean components to use for the model, one
value per field. If all values are zero, then all
components in all fields are used. If any value is not
zero, then abs(NCOMP(i)) (or fewer depending on FLUX and
negativity) components are used for field i, even if
NCOMP(i) is zero. If any of the NCOMP is less than 0,
then components are only used in each field i up to
abs(NCOMP(i)), FLUX, or the first negative whichever
comes first. If abs(NCOMP(i)) is greater than the number
of components in field i, the actual number is used. For
NCOMP = -1,0
says to use one component from field one unless it is
negative or < FLUX and no components from any other
field. This would usually not be desirable.
NCOMP = -1000000
says to use all components from each field up to the
first negative in that field.
NCOMP = -200 100 23 0 300 5
says to use no more than 200 components from field 1, 100
from field 2, 23 from field 3, 300 from field 5, 5 from
field 6 and none from any other field. Fewer are used if
a negative is encountered or the components go below
FLUX.......Only components > FLUX in absolute value are used in the
NMAPS......Number of image files to use for model. For multi-scale
models, set NMAPS = NFIELD * NGAUSS to include the Clean
components of the extended resolutions. If more than one
file is to be used, the NAME, CLASS, DISK and SEQ of the
subsequent image files will be the same as the first file
except that the LAST 3 or 4 characters of the CLASS will
be an increasing sequence above that in IN2CLASS. Thus,
if INCLASS='ICL005', classes 'ICL005' through 'ICLnnn'
or 'ICnnnn', where nnn = 5 + NMAPS - 1 will be used. Old
names (in which the 4'th character is not a number) are
also supported: the last two characters are '01' through
'E7' for fields 2 through 512. In old names, the highest
field number allowed is 512; in new names it is 4096.
CMETHOD....This determines the method used to compute the
model visibility values.
'DFT' uses the direct Fourier transform, this
method is the most accurate.
'GRID' does a gridded-FFT interpolation model
' ' allows the program to use the fastest
NOTE: when using a model derived from data with
difference uv sampling it is best to use 'DFT'
CMODEL.....This indicates the type of input model; 'COMP' means that
the input model consists of Clean components, 'IMAG'
indicates that the input model consists of images.
'SUBI' means that the model consists of a sub-image of
the original IMAGR output. If CMODEL is ' ' Clean
components will be used if present and the image if not.
SUBI should work for sub-images made with DO3DIM true and
sub-images of the central facet made with DO3DIM false,
but probably will not work well for shifted facets with
DO3DIM false. Use BLANK rather than SUBIM in such cases.
CALIB will set a scaling factor to correct image units
from JY/BEAM to JY/PIXEL for image models. If the source
table contains a flux, then that flux will be used to
scale the components model to obtain the stated total
flux. This is needed since initial Cleans may not obtain
the full flux even though they represent all the
essentials of the source structure.
SMODEL.....For a single source file the model described by SMODEL is
used instead of a CLEAN components model if IN2NAME = ' '
and IN2CLASS = ' '. For a multi-source file a point
source with flux from the SU table is used instead of the
CLEAN components if IN2NAME = ' ' and IN2CLASS = ' '.
If IN2NAME and IN2CLASS are specified, then SMODEL is
required to be <= 0. If IN2NAME or IN2CLASS is blank,
then, for single-source files, SMODEL(1) is required to
be > 0.
SMODEL(1) = flux density (Jy); 0 => no SMODEL.
SMODEL(2) = X offset in sky (arcsec)
SMODEL(3) = Y offset in sky (arcsec)
SMODEL(4) = Model type:
0 => point model
1 => elliptical Gaussian and
SMODEL(5) = major axis size (arcsec)
SMODEL(6) = minor axis size (arcsec)
SMODEL(7) = P. A. of major axis (degrees)
2 => uniform sphere and
SMODEL(5) = radius (arcsec)
The following specify the output file to be written if the
input file is a single source file.
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #). 0 => highest unique
OUTDISK....Disk drive # of output UV file. 0 => highest
disk number with space
The following control how the solutions are done, if you don't
understand what a parameter means leave it 0 and you will
probably get what you want.
REFANT.....The desired reference antenna for phases.
SOLINT.....The solution interval (min.)
0 => scan average for multi-source,
0 => 10 s for single source amp-phase solns. (VLA)
0 => 10 min for delay-rate solutions (VLBA).
CALIB tries hard to make equal integrations within each
scan but that is a problem that lacks a general solution.
You can help by careful choice of SOLINT: assume you have
data every 10 seconds. Then, to get 1 sample per
solution, set SOLINT=9/60. To get 2 per solution, set
SOLINT=19/60, 3 per solution SOLINT=29/60. Each averaged
interval will start with an actual data sample and will
end just before the first sample at a time greater than
the start + SOLINT + 0.1s. At the end of the scan, the
end time can be increased by up to 0.6 * SOLINT to
prevent short final integrations. For calibration that
is not self-calibration, note that the 2-point
interpolation will use ONLY the last integration of a
calibrator scan with the first integration of the next
calibrator sacn. That is why the initial calibration
normally uses scan averages for the calibrator sources.
If the times in your data set are not at regular
intervals due to flagging and averaging, you must be
careful with SOLINT. To get all data in 10 seconds (from
0 through 9.999) set SOLINT to 9.999/60. Use of 1 sec
will do odd things with the records at odd times.
SOLSUB.....The begin time for the next interval in advanced from the
current one by SOLINT / SOLSUB where 1 <= SOLSUB <= 10.
0 -> 1. This is to produce solutions at sub-intervals of
SOLINT based on SOLINT length of averaging.
SOLMIN.....Minimum number of subintervals to be used in a solution.
0 -> SOLSUB.
APARM......General control parameters.
APARM(1)...Minimum number of antennas allowed for a solution.
0 => max (3, min (6, Numant/2))
APARM(2)...If > 0 then the input data has already been
divided by a model; only solutions will be
APARM(3)...If > 0 then average RR, LL
APARM(5)...If > 0 then make a combined solution for the IFs;
if <= 0 then make separate solutions.
APARM(6)...Print flag, 0=none, 1=time, closure error statistics,
2=individual closure failures (exceeding both CPARM(7)
sigma and either MINAMPER or MINPHSER), 3=some additional
info including the antenna signal to noise ratio,
4=solutions, 5=data too.
APARM(7)...The minimum allowed signal-to-noise ratio. 0 => 5
APARM(8)...If there is no antenna (AN) table with the input file
then the maximum antenna number in the file should be
entered in APARM(8).
APARM(9)...When solutions fail or there is insufficient data and
APARM(9) > 0 then (1,0) is written to the SN table. This
will preserve the previous calibration but this option
should be used with extreme care.
APARM(10)..When writing a single-source output file, calibrate the
output weights except when either DOCAL > 99 or
APARM(10) > 99 or both.
DOFLAG.....If DOFLAG > 0, those baselines with excessive closure
error will be added to a new flag table along with all
flags previously in FLAGVER. If DOFLAG <= 0, no new data
flags are generated and no flag table is written. In
either case, all SOLTYPEs below check the data for
closure error and will report the fractions for which the
closure error exceeds abs(DOFLAG) times the rms closure
error. Defaults for the reporting level are:
0.0 < DOFLAG < 2.0 -> 2.5
-1.0 < DOFLAG <= 0.0 -> -2.5 if APARM(6) = 0
-99.0 if APARM(6) >= 1
Note that this checking of closure error is in addition
to the checking done under control of MINAMPER, MINPHSER,
and APARM(6) which do not flag the data. Note that data
marked as "bad" by the DOFLAG test will not be checked
with the APARM(6) controlled tests. The default on
DOFLAG=0 is then meant to enable better printing of
closure errors when not doing any actual flagging.
' ' => normal least squares,
'R ' => as ' ' with robust iteration
'L1 ' => L1 solution; a weighted sum of the moduli
of the residuals is minimized.
The computed gain solutions are less
influenced by wild data points, but there
is some loss of statistical efficiency.
See [F.R. Schwab, VLA scientific Memo #136]
for further details.
'L1R ' => as 'L1' with robust iteration
'GCON' => least squares which may include gain
'GCOR' => as 'GCON' with robust iteration
SOLTYPE (other than the R) is ignored when the DOFIT
option is used. The robust versions iterate the
solution, discarding data that does not fit the current
solution well enough. They should be less disturbed by
bad data, but will be slower.
'A&P ' => amplitude and phase.
'P ' => phase only
'P!A ' => phase only (no amplitude information)
'GCON' => amplitude and phase with constraints on
amplitude. This mode requires setting
SOLTYPE='GCON', uses GAINERR and
SOLCON may be used.
' ' => 'A&P ' for multisource (raw) data,
=> 'P ' for single source data.
SOLCON.....Gain constraint factor; a value larger than 0 will
increase the strength of the amplitude constraint
in gain constrained solution with SOLMODE='GCON'
MINAMPER...Amplitude closure error regarded as excessive in per cent.
If APARM(6) > 0, summaries of the number of excessive
errors by antenna are printed and, if APARM(6) > 1, up to
1000 of the individual failures are printed. 0 => do not
check or report "excessive" closure errors of any sort.
Note that amplitude closure errors are accumulated using
logarithms so that gains of 0.5 and 2.0 are both errors of
MINPHSER...Phase closure error regarded as excessive in degrees.
If APARM(6) > 0, summaries of the number of excessive
errors by antenna are printed and, if APARM(6) > 1, up to
1000 of the individual failures are printed. 0 => do not
check or report "excessive" closure errors of any sort.
NORMALIZ...If > 0, constrain the mean gain modulus of the calibration
applied to be unity. This is mostly used in self
calibration. If NORMALIZ = 1, the mean is over all IFs,
antennas, polarizations and subarrays. If NORMALIZ =2,
it is the same except separated by subarray. If NORMALIZ
= 3, it is averaged over all antennas and polarizations
but separated by IF and subarray. NORMALIZ=4 also
separates by polarization. If you select NORMALIZ= 1,
the global scaling factor is written to the header of the
SN table. For options 2 - 4, the SN table is re-written
with the final scaling applied. If = 0, substitute
CPARM(2) which was previously used for this information.
CPARM(1)...Minimum elevation in degrees for the solutions used to
constrain the mean gain modulus. 0 or >80 => no
constraint (actually -100 is used).
CPARM(2)...If NORMALIZ > 0, CPARM(2) controls whether a mean value
(CPARM(2) <= 0) or a median value (CPARM(2) > 0) is used.
CPARM(3)...If > 0, the values of any amplitude closure errors whose
average absolute percentage value exceeds CPARM(3) will be
printed if APARM(6) > 0.
CPARM(4)...If > 0, the values of any phase closure errors whose
average absolute value exceeds CPARM(4) degrees will be
printed if APARM(6) > 0..
CPARM(5)...If > 0 then the amplitudes will be scalar averaged when
averaging across times before determining the solutions.
The averaging of spectral channels will be a vector
average unless CPARM(5) > 1.5. Vector averaging is
preferred to avoid the Ricean bias in amplitudes, but not
when phase instability will make the signal incoherent.If
the atmospheric phase is very unstable, then it should be
fine at any one time but may require the scalar averaging
CPARM(6)...The robust solution method discards data more than
f(iter) * rms(iter)
from the current solution to find the iter+1 solution
f(iter) = max (g(iter), CPARM(6)) and
g = 7.0, 5.0, 4.0, 3.5, 3.0, 2.8, 2.6, 2.4, 2.2, 2.5.
Thus CPARM(6) can be used to limit the discarding to less
CPARM(7)...The printing of individual closure errors occurs only if
APARM(6) >= 2 and the errors exceed MINAMPER percent in
amplitude and/or MINPHSER degrees in phase. That
printing is also limited to those errors that are more
than CPARM(7) times the 1 sigma expected error (based on
the data weights). 0 -> 2.5. If you want no limit,
set CPARM(7) to something like 0.001.
SNVER......The version of the SN table to write the solutions
to. If =0, a new SN table is generated. It is forced to
0 always for single-source files.
ANTWT......Antenna weights. These are additional weights
to be applied to the data before doing the
solutions, one per antenna. Use PRTAN to
determine which antenna corresponds to each
0 => 1.0
GAINERR....Estimates of the standard deviation of the modulus
of the gains for each antenna. These are used
ONLY if SOLMODE and SOLTYPE='GCON'. The solution
will attempt to make the standard deviation of
the modulus of the antenna gains match these
values so accurate values are essential.
BADDISK....Disk numbers on which scratch files are not to
CALIB: Task to determine antenna gains from calibrator data
Related Programs: CLCAL, LISTR, SPLIT, UVFLG
This task is the central AIPS routine for calibrating multi-
source uv data sets using observations of calibration sources
that can either be assumed to be point sources or have well
CALIB determines antenna voltage gain solutions (amplitude
and/or phase) from data for calibrator sources with well known
flux densities, positions and structures. It is the equivalent
of the VLA Dec-10 ANTSOL (with additional options) and of a
combination of the AIPS routines ASCAL and VSCAL. Solutions
determined by CALIB under control of the APARM, CPARM and DPARM
parameters are written to the solution (SN) extension table of
the input uv data set. Solution tables may be merged, smoothed
and interpolated into calibration (CL) tables for multi-source
uv data files using CLCAL.
CALIB may also be run on files containing data for only one
source, for self calibration.
To run CALIB, you should specify at least:
The input uv data file (INNAME, INCLASS, INSEQ, INDISK).
The CALSOURces to be used for determining antenna gains, or
leave CALSOUR blank and specify a CALCODE and/or qualifier.
REFANT, the reference antenna for the solution (choose an
antenna with good signal to noise that was present through
as much of the observing as possible).
The defaults are set so that running CALIB on a multi-
source uv data file setting only these inputs will make
a solution file for all IFs in the data over the entire
time range using the highest-numbered flag file. All
antennas will be calibrated for amplitude and phase, using
data from the entire uv range. All antennas will be equally
weighted. Point source models will be assumed for the
calibration sources. The solution will be written to an
Other useful options
Use APARM(6)=3 to list the signal to noise ratio at each
antenna solution. Solutions with signal to noise below
5:1 are probably not meaningful and will be discarded by
the default setting of APARM(7). You may wish to apply
more stringent criteria with APARM(7).
Use SOLTYPE and SOLMODE='' to solve for both amplitude and
phase solutions simultaneously with no constraints on amplitude,
SOLTYPE and SOLMODE='GCON' for amplitude and phase with
constraints set by GAINERR and SOLCON. Amplitude solutions
for point source models in multisource files will be based on
the flux densities entered for the sources in the source (SU)
table extension of the data set using task SETJY.
Use UVRANGE and WTUV to weight different uv ranges
differently (or to restrict the solution to some uv range
-- WTUV = 0 is read as zero weight).
"CLEAN" COMPONENT MODELS
CALIB does not restrict you to the use of point source models
for your calibrators. Use IN2DISK, IN2NAME, IN2SEQ, INVERS,
NCOMP and NMAPS to specify a CLEAN component model for the
field or fields around a calibrator and specify that
calibrator in SOURCE. CALIB will create an SN table for that
calibrator alone. This SN table may then be merged with SN
tables for other calibrators produced by other runs of CALIB,
when the SN tables are smoothed and interpolated into a CL file
FLUX CALIBRATOR MODELS
This is actually a subsection of CLEAN COMPONENT MODELS above.
You are strongly encouraged to use the flux calibrator models
available for all the primary flux calibrators (3C138, 3C147,
3C286 and 3C48). Using calibrator models removes the need set
UVRANGE and ANTENNAS. To see what calibrator models are available
in AIPS type CALDIR, to read them in use the task CALRD. CALRD
loads in the selected model as an image file. Then specify this
image in IN2DISK, IN2NAME, IN2CLASS and IN2SEQ. CALIB will
recognize these images as standard calibrator models and scale
the clean components in the central part of the field with the
flux in the SU table.
RESETTING YOUR CALIBRATION
The first version of the CL table attached to your uv data set
is protected from modification in CLCAL, so
that you can easily "undo" all calibration steps that have
taken place within AIPS. To reset your calibration, delete all
CL tables with version numbers >1, and delete all SN tables.
POLARIZATION considerations (thanks to Robert Braun)
The VLA measures approximately (neglecting the leakage terms):
RR=I+V, LL=I-V, RL=Q+iU, LR=Q-iU
The WSRT uses linear polarization but the equatorial mounts mean that
the feed orientation remains constant relative to the sky (no
parallactic angle change at all). Thus, the WSRT measures
XX=I-Q, YY=I+Q, XY=-U+iV and YX=-U-iV
If you compare these two sets of equations, you see that they have a
lot in common. If you simply pretend that you have measured
(RR,LL,RL,LR) by changing the Stokes value from -5 to -1 in the header
with PUTHD, you're almost in business, except you have -Q in the place
of V, -U in the place of Q, and V in the place of U. This is fine for
most things, since you just have to request a slightly different
parameter from the one you really mean.
The biggest hassle comes from amplitude calibration of linearly
polarized sources, like:
3C286 (near 1.4 GHz) which has (I,Q,U,V)=(14.65,0.56,1.26,0.00) Jy
3C138 (near 1.4 GHz) which has (I,Q,U,V)=(8.30,0.63,-0.17,0.00) Jy
Since Q is non-zero, it means that the XX and YY correlations do not
correspond to the same real flux density (ie. XX=I-Q and YY=I+Q).
Now, since RR=I+V and LL=I-V, the idea is to have CALIB use the
Stoke's V from the SU table. The, for WSRT data, one can fudge the
right behavior, by putting the source's actual value of -Q in place
of V in the SU table.
This shouldn't harm any VLA users, since Stoke's V is near enough zero
for most sources anyway. And if it were non-negligible it should be
taken along in any case, since it really does affect the RR and LL
correlations, and therefore the derived gain of the R and the L IFs.