As of Wed Jun 12 10:17:43 2024

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
                                   (NORMALIZ>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.

                                   Model file: Clean map or
                                      matching UVSUB 'MODL'
IN2NAME                               Model name (name)
IN2CLASS                              Model name (class)
IN2SEQ            0.0     9999.0      Model name (seq. #)
IN2DISK           0.0        9.0      Model 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:
                                   'DFT','GRID','    '
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
                                           single source
                                   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
                                   Phase-amplitude Parameters:
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         6.0  >0 => normalize gain:
                                     1 globally, 2 by subarray,
                                     3 by subarray,IF
                                     4 by subarray,IF,pol
                                     5 by IF
                                     6 by IF,pol
CPARM                              Phase-amp. parameters
                                      1 = Min el for gain
                                           normalization (deg)
                                      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
                                        between times
                                        >= 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.
DOHIST                             >= 0 write history to input
                                        file in all cases
BADDISK                            Disk no. not to use for
                                      scratch files.


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

       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 VV = I-Q and HH = 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.

       Real linear polarization may also be calibrated with point
       sources of known Q and U polarization.  Make sure that the
       Q and U values are in the source table and do not average the
       VV and HH polizations (APARM(3)).  There is also no current
       way to make a divided data set in advance (APARM(2)).  The
       task will divide VV by I + Qcos(p1+p2) + Usin(p1+p2) and HH
       by I - Qcos(p1+p2) - Usin(p1+p2) where p1 and p2 are the two
       antenna parallactic angles.  Note that the task cannot handle
       model images in this mode, even for the Ipol model.

       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.

       The task writes the SNR to the SN table as weights.  If failed
       solutions are passed as gain = (1,0) the weight is set to 1.
       If a solution fails, the weight is set to -1. If there are no
       data samples for a particular antenna the weight is set to -2.
       If there are only one or two samples for an antenna in a
       successful solution, the weight is set to SNRmin+1 (APARM(7)+1
       or 6 by default).  This weight is also set when the antenna is
       used in a solution, but the gain of that antenna is not solved
       (DOFIT option).  The weights may now be used for editing in
  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
             calibrator code:
                  '    ' => 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.
             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
             of WTUV.
  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: DOCALIB true is now allowed for
             single-source files but it makes an unworkable situation
             of two SN tables which cannot be combined.  Use this option
             on single-source files only to test the quality of the
             calibration.  In such cases, CALIB sets DOAPPLY=-1.
  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.  In 31DEC24, IN2NAME may
also specify the output of UVSUB OPCODE='MODL' which matches the
current INNAME, INCLAS, INSEQ data set.  The current INNAME file with
DOCAL and FLAGVER applied may have fewer samples than in IN2NAME but
they must still be in the same order.  Adverbs INVERS, NCOMP, FLUX,
NCOMP, CMETHOD, and CMODEL when the model is a uv data file written
by UVSUB (although these adverbs can appliy in UVSUB).
  IN2NAME....Model 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 or a UVSUB MODL 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 (as a function of IF)
             found in the SU table.  If that flux is zero, no scaling
             is done.
  IN2CLASS...Model name (class).     ' ' => not Clean model.
  IN2SEQ.....Model name (seq. #).    0 -> highest.
  IN2DISK....Disk drive # of model.  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
  DOAPPLY....>= 0 -> write the output if single source and
                     APARM(2) <= 0
             < 0  -> don't write ever
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.
  Phase-amplitude parameters:
  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.
  SOLTYPE....Solution type:
               '    ' => 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.
  SOLMODE....Solution mode:
              '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
             100 percent.
  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.  NORMALIZ=5 separates only by
             IF (combining subarrays).  NORMALIZ=6 separates by IF and
             polarization.  If you select NORMALIZ= 1, the global
             scaling factor is written to the header of the SN table.
             For options 2 - 6, the SN table is re-written with the
             final scaling applied.  If = 0, substitute CPARM(2) which
             was previously used for this information.
  CPARM......Phase-amplitude parameters.
  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
             between times.
  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
             restrictive values.
  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
             antenna number.
             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.
  DOHIST.....>= 0 write full history to input file even if writing an
                  output file
             < 0  write full history to output file only or, if no
                  output file, to input file
  BADDISK....Disk numbers on which scratch files are not to
             be placed.


CALIB:  Task to determine antenna gains from calibrator data
Documentor:  A.H.Bridle
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
determined structures.

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
SN table.

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).


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

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.


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

VV=I-Q, HH=I+Q, VH=-U+iV and HV=-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 VV and HH correlations do not
correspond to the same real flux density (ie. VV=I-Q and HH=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.