AIPS HELP file for EVACL in 31DEC25
As of Tue Dec 10 5:29:32 2024
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