AIPS NRAO AIPS HELP file for EVACL in 31DEC22



As of Sun Dec 4 9:10:54 2022


EVACL: evaluates statistics in phase and amplitude closures

INPUTS

INNAME                             UV data (name).
INCLASS                            UV data (class).
INSEQ             0.0    9999.0    UV data (seq. #).  0 => high
INDISK            0.0       9.0    Disk unit #.  0 => any
STOKES                             Stokes' parameter - only 1
BIF               0.0      100.0   First IF to consider, 0=>1.
EIF               0.0      100.0   Last IF to consider
BCHAN             0.0              First channel to average
ECHAN             0.0              Last channel in average
FLAGVER                            Flag table version, 0->high
ANTENNAS                           Antenna numbers to include
                                   or omit.
OPCODE                             'INDE' -> independent
                                      triangles/quadrangles
                                   else all.
SOLINT                             Time interval (minutes) over
                                   which to average to form
                                   closure phases and amplitudes

HELP SECTION

EVACL
Type:  Task
Use:   Examines the statistics in a UV data set which should be a
       single-source only.  The task forms closure phases and
       closure amplitudes over averages of SOLINT minutes and
       then looks at the mean and rms of these over all times and
       all triangles/quadrangles.  The results are printed as a
       function of IF.  Tasks CLPLT and CAPLT will do this for
       selected triangles/quadrangles plotting as a function of
       time.

       Closure amplitude in the quadrangle of antennas a, b, c, and d is
       defined as
             LN [ (amp_ab * amp_cd) / (amp_ac * amp_bd) ]
       which should be independent of any antenna-based instrumental
       gains.  Closure phase in the triangle of antennas a, b, and c is
       defined as
                  Phase_ab - Phase_ac + Phase_bc
       which should be independent of any antenna-based instrumental
       phases.  Since these apply to the RR and LL, closure amplitude
       and phase are only meaningful in STOKES 'RR' or 'LL', not in
       STOKES 'I' or any other compund Stokes parameter or
       cross-polarization.  EVACL will allow you to compute these, but
       they are not expected to be meaningful.

       Closure amplitude and phase are not zero when there is real
       source structure.  Therefore, you might wish to divide your data
       by your model with OOSUB or UVSUB, and then compute the closure
       amplitudes and phases from the resulting "gains" which ideally
       act like a point source at the origin (if your model is really
       wonderful).  EVAUV does this.

         Closure information is produced by the following tasks:
         CLPLT   Plots closure phases for individual triangles as a
                 funtion of time.
         CAPLT   Plots closure amplitudes for individual quadrangles as
                 a funtion of time.
         EVACL   Computes the RMS of closure phase and amplitude as a
                 function of IF for an individual Stokes.
         EVAUV   Computes two data sets: data-model and data/model.  The
                 closure RMSes of the latter may be computed as
                 functions of polarization and IF.  Other statistics
                 are computed and plotted.
         CLOSE   Computes the RMS closure phase or amplitude as a
                 function of spectral and IF channel.  A plot is
                 produced and a text file may be written.

Adverbs:
  INNAME.....UV file name (name).       Standard defaults.
  INCLASS....UV file name (class).      Standard defaults.
  INSEQ......UV file name (seq. #).     0 => highest.
  INDISK.....Disk unit #.               0 => any.
  STOKES.....Specifies the single Stokes type to be computed.
             Recognized values are 'I', 'Q', 'U', 'V', 'RR', 'LL', 'LR',
            'RL', 'VV', 'HH', 'VH', 'HV'.    '  ' => 'I'.
  BIF........Lowest IF to consider.   0 -> 1
  EIF........Highest IF to consider.  0 -> highest
  FLAGVER....specifies the version of the flagging table to be
             applied. 0 => highest numbered table.
             <0 => no flagging to be applied.
  ANTENNAS...A list of the antennas which if all > 0 are to be included
             or if, any one or more are < 0, are to be omitted.
             All 0 -> all included.
  OPCODE.....'INDE' -> select only independent triangles, e.g.
                       1,2,3 then 2,3,4 then 3,4,5, etc.
             else -> select all triangles/quadrangles
  SOLINT.....The time interval (minutes) over which to average the data
             in order to form the closure phase and amplitude. It is
             possible, with editing and especially on correlators which
             only correlate a subset of the available stations
             simultaneously that the time tags associated with
             visibility values on different baselines differ. Therefore
             one has to specify a time interval over which to average
             the data to form the closure phase and amplitude. If this
             is not necessary with your data, set
                  SOLINT <= 0.9 * data integration time.
             You should experiment a little with this parameter. If the
             fringe rate for the source is fairly rapid, then it is very
             important to have the sampling be the same on all baselines
             in each triangle.  Otherwise, samples at slightly different
             times will be combined but the phases and amplitudes will
             not cancel properly.  Use of a very small value of SOLINT
             (but > 0) will cause inadequately aligned data to be
             discarded in order to avoid misleadingly high closure
             phases and amplitudes.
             If SOLINT < 0, the task will form a closure phase/amplitude
             as soon as it has accumulated at least one sample for each
             of the three/four baselines in the triangle/quadrangle.

EXPLAIN SECTION


AIPS