AIPS NRAO AIPS HELP file for UVAVG in 31DEC18



As of Sun Apr 22 8:24:58 2018


UVAVG: Task to average or merge 'BT' or 'TB' sorted UV data.

INPUTS

INNAME                             Input UV file name (name)
INCLASS                            Input UV file name (class)
INSEQ             0.0     9999.0   Input UV file name (seq. #)
INDISK            0.0        9.0   Input UV file disk unit #
SOURCES                            Source name
QUAL            -10.0              Calibrator qualifier -1=>all
CALCODE                            Calibrator code '    '=>all
TIMERANG                           Time range to use
SELBAND                            Bandwidth to select (kHz)
SELFREQ                            Frequency to select (MHz)
FREQID                             Freq. ID to select.
SUBARRAY          0.0     1000.0   Sub-array, 0=>all
BIF                                Low IF number to do
EIF                                Highest IF number to do
BCHAN             0.0              First channel included
ECHAN             0.0              last channel included
DOCALIB          -1.0      101.0   > 0 calibrate data & weights
                                   > 99 do NOT calibrate weights
GAINUSE                            CL (or SN) table to apply
DOPOL            -1.0       10.0   If >0.5 correct polarization.
PDVER                              PD table to apply (DOPOL>0)
BLVER                              BL table to apply.
FLAGVER                            Flag table version
DOBAND           -1.0       10.0   If >0.5 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.
DOACOR                             Include autocorrelations?
OUTNAME                            Output UV file name (name)
OUTCLASS                           Output UV file name (class)
OUTSEQ           -1.0     9999.0   Output UV file name (seq. #)
OUTDISK           0.0        9.0   Output UV file disk unit #.
XINC              0.0              Write every XINC'th record.
YINC              0.0              Averaging time (sec).
ZINC              0.0              Time (secs) to which data
                                   were pre-averaged. It must be
                                   close to the true one.
                                   0 => ignore
OPCODE                             'MERG' for Merge function.
                                   Anything else for average.
OPTYPE                             'CROS' - merge xc data
                                   'AUTO' - merge ac data
                                   Anything else => merge all.
                                   ac data requires DOACOR > 0
FQCENTER                           >= 0 -> center frequency axis

HELP SECTION

UVAVG
Task: This task will average or merge a 'BT' or 'TB' sorted uv data
      set in time.  The input UV file can be either single- or
      multi-source.  In the latter case, UVAVG averages each source
      separately.  Times in each averaging interval may be identical
      on output or represent the exact average time for each
      baseline.  Multiple subarrays may be done with or without the
      calibration.
Adverbs:
  INNAME.....Input UV file name (name). Sort must be 'BT'
             or 'TB'.  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.
  SOURCES....Source to be baselined.   '  '=> all; if any starts with
             a '-' then all except ANY source named.
  QUAL.......Qualifier of source to be baselined. -1 => all.
  CALCODE....Calibrator code of sources to baseline. ' '=> all.
  TIMERANG...Time range of the data to be copied. In order: Start day,
             hour, min. sec, end day, hour, min. sec. Days relative to
             ref. date.
  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. For data which contain multiple
             bandwidths/frequencies the task will insist that some form
             of selection be made by frequency or bandwidth.
  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.
  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 that case, the task
             will request that you use FREQID.
  SUBARRAY...Sub-array number to copy. 0=>all.
  BIF........First IF to include.  0 -> 1.
  EIF........Last IF to include.   0 -> max.
  BCHAN......First channel to copy. 0=>all.
  ECHAN......Highest channel to copy. 0=>all higher than BCHAN
  DOCALIB....If true (>0), calibrate the data using information in the
             specified Cal (CL) table for multi-source or SN table for
             single-source data.  Also calibrate the weights unless
             DOCALIB > 99 (use this for old non-physical weights).  If
             the data are not in time order, then DOCALIB must be
             false.  Multiple sub-arrays may include calibration -
             they are done one at a time.
  GAINUSE....Version number of the CL table to apply to multi-source
             files or the SN table for single source files.
             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.
             If the data are not in time order, then BL tables may not
             be applied and BLVER should be set to -1 if any are
             present.
  FLAGVER....specifies the version of the flagging table to be applied.
              0 => highest numbered table.
             <0 => no flagging to be applied.
  DOBAND.....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
             corrected.
             (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
             corrected.
             If the data are not in time order, then only DOBAND=1 may
             be used.
  BPVER......Specifies the version of the BP table to be applied
                0 => highest numbered table.
               <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
               SMOOTH(2).
  DOACOR.....> 0 => include autocorrelations as well as cross
             correlation data.
  OUTNAME....Output UV file name (name).    Standard defaults.
  OUTCLASS...Output UV file name (class).   Standard defaults.
  OUTSEQ.....Output UV file name (seq. #).  Standard defaults.
  OUTDISK....Disk drive # of output UV file. 0 => highest with
             space for the file.
  XINC.......Write only every XINC'th output record.
  YINC.......Averaging time (sec).   < 0.2 => 0.2  The intervals are
             handled differently for TB and BT data - see the EXPLAIN
             file for details.  The latter attempts to make intervals
             at integer*YINC spacing through the day; the former
             averages data within YINC of the first sample in the
             interval.  If you have data at 1.0 sec intervals and want
             10.0 sec intervals out, do NOT set YINC to 10, expecially
             for TB-sorted data.  Set it to e.g. 9.5 so that the first
             sample 10.0 sec from the first sample in the current
             interval will cause the start of a new interval.
  ZINC.......Time (sec) to which data have already been pre-averaged.
             UVAVG uses this to estimate the size of the output file.
             0 => ignore.  This must be the correct input average time
             for the merging function.
  OPCODE.....'MERG' selects the data with the highest weight within
             each YINC seconds.  This is used primarily on VLB data
             where some baselines are repeated in processing and for
             putting together polarization or spectral line data sets.
             Any other OPCODE, simply averages the input data over
             YINC seconds.  Note that the MERG operation is
             particularly sensitive to the choice of YINC and you MUST
             set YINC less than the interval between samples that you
             wish to retain.  Thus if your data are at 10.0 sec
             intervals and you set YINC to 10.0, you will discard half
             your data and end up with a data set on 20 second
             intervals.  With BT sorted data the affect is less
             predictable and you may get more or less what you want or
             you may not.  If data to be merged are e.g. within 1 sec
             of each other whilst data to be retained are, say 2 sec
             apart, then set YINC to 1.1 or even 1.5 but NOT 2.0.
                       --------------------------
             Averaging intervals are determined in two ways.  The
             default is to start each interval with the time of the
             first sample in that interval and continue YINC seconds.
             The default from that point causes each baseline from the
             interval to be written with the exact average time of
             that baseline (carefully sorted into time order).
             'TIME' says to write out the data from an averaging
             interval with the same average time.
             'GRID' makes each time interval be an integer number of
             YINC intervals since time zero.  The times written are at
             the center of that interval.
             'GRIT' is like grid but each baseline is written with the
             exact average time for that baseline.  BT sorted data use
             GRIT by default unless GRID is specified.
  OPTYPE.....'AUTO' - just merge autocorrelation spectra;
             'CROS' - just merge cross-power spectra;
             '    ' - merge both.
             Adverb only used in MERG mode.
             NOTE: DOACOR must be true or auto-correlation data are
             not passed through the task at all.  DOACOR is forced to
             be true when MERG and AUTO are specified.
  FQCENTER...>  0 => Change frequency axis reference pixel to
                     Nchan / 2 + 1
             else => do not change reference pixel

EXPLAIN SECTION

UVAVG:  Task to average 'BT' or 'TB' sorted UV data
DOCUMENTOR: R. C. Walker  NRAO/CV
RELATED PROGRAMS:  UVSRT

                   PURPOSE

     UVAVG averages or merges 'BT' or 'TB' sorted uv data bases.  The
average function is especially useful if a large data base can be
reduced in size to make it more manageable.  Care should be taken that
the average time is not so long that 'time average smearing' occurs -
ie. that the longer baselines sweep through enough uv space in an
integration interval to smear significant structure.  Note that task
UBAVG will average the data in a baseline-length dependent way that
avoids this smearing but which makes later self-cal problematical.
IMAGR will perform the action of UBAVG on the fly to reduce the size
of its work file if requested.
     Averaging is often used after VBFIT on VLBI data.  Longer
averages are allowed at that point because relatively high residual
fringe rates due to atmosphere etc have been removed.
     The merge function in UVAVG replaces VBMRG and works on 'TB' or
'BT' data with the same restrictions as for averaging.  This function
is used to eliminate duplicate data after multi-pass VLBI processing
and to form full polarization or many channel spectral line data bases
from separate channel inputs.  The input data sets must have records
long enough to hold the full number of channels - see DBCON if changes
need to be made.
     UVAVG can be used to thin out a data set while leaving it
properly configured for self cal.  If XINC greater than 1 is
specified, UVAVG will only write every XINC'th output.  If the input
data is in 'TB' sort order, all baselines for every XINC'th time
interval are written so that complete data sets for each time remain
and can be self-cal'ed.  This function should be useful, for example,
if a small data set sharing about the uv coverage of the main data set
and not subject to time average smearing is desired for the first few
iterations of hybrid mapping or self cal.  The function works in
either the merge or average modes.
     There should no longer be a limitation on the product of the
number of baselines and the number of words per visibility record that
can be averaged if the input sort order is 'TB'.  Dynamic memory is
used to an appropriate buffer is allocated.  There must be adequate
virtual memory in your machine to handle the problem.

     The time windows used for merging or averaging are of a length
set by YINC and are timed such that one record begins at 0 hours UT
(not IAT) when the data are in BT order or OPCODE = 'GRID' or 'GRIT'
is specified.  Other OPCODE values with TB ordered data cause the
interval to begin with the first sample in that interval and extend
YINC seconds from there.

     UVAVG marks the data with a time that is the weighted average
time of the data when averaging and is the time of the record
containing the last accepted correlator data when merging.  For most
purposes, this is more exact.  But the lack of agreement in time
between samples can cause difficulties with averaging in other tasks
such as CALIB and TVFLG and with other software packages such as
CalTech's.  OPCODE = 'TIME' will cause TB data to be written with the
same time for all baselines in each interval, that time being the
weighted average of all times over all baselines withing that
interval.  OPCODE='GRID' will cause TB and BT data to be assigned the
mid-point of each YINC gridded interval no matter what the average
time might be.  Ungridded times, when transfered to the Caltech
package, are treated as separate points by VBCIT.  This does not work
well in the Caltech format.  To avoid the problem, use GRID or TIME,
or average the data in the Caltech package or UVAVG output can be run
through the Caltech averaging program with the same average time that
was used in UVAVG.  The records should be properly combined in this
way.

                   COMMENTS

XINC:
     This controls the output.  It should be an integer and causes
only every XINC'th record to be written.  For 'TB' sorted data, all
baselines for every XINC'th time interval are written so the data set
may still be self-caled.

YINC:
     This sets the averaging time in seconds.  For averaging, specify
the output average time.  For merging, specify less than the input
average time.  If YINC is not correctly specified, the merging
function may not behave correctly.  If it is long enough to just
encompass two samples you wish to retain, then one will be discarded
and you will not get what you expect.
     The averaging intervals are managed in different ways for data in
BT and TB order.  For TB order, an interval starts with the first
sample and includes all samples within YINC seconds.  The next
interval begins with the first sample beyond the end of the first
interval and goes for another YINC seconds, and so forth.  In BT
order, however, we attempt to align the averaging intervals for all
baselines by averaging in intervals of YINC seconds beginning at time
0 for the given day.  This may cause there to be two output records
for a particular baseline when you ask for an averaging interval
somewhat greater than a scan length if the times span these integer
times YINC intervals.  When merging, YINC should be rather less than
the averaging time for TB data and should be just a hair less than the
averaging time for BT data.

ZINC:
     ZINC defines the pre-average time interval in seconds, i.e. the
time to which the data in the input file have already been averaged.
     If ZINC is set to 0 then the output file created will initially
be as large as the input file. After UVAVG has finished the unused
disc space allocated to the output file will then be released. If ZINC
is nonzero then UVAVG will estimate the size of the output file needed
(plus a little extra, just in case..) and will still shrink it after
it has finished if necessary. The use of ZINC is recommended if
particularly large files are being averaged.

OPCODE:
     If OPCODE='MERG' is specified, UVAVG selects data from one
input record for each YINC time interval.  The data selected
for different correlators (polarizations, spectral channels
etc.) can come from different input records.  Normally either
the record with the highest weight, or, if the weights are
equal, the last record in, are selected.  If the weights
are equal and the amplitudes differ by more than a factor of
two, the record with the highest amplitude is selected.  The
u, v, w, time, etc in the output record are those of the
last bit of data selected, regardless of polarization etc,
for that output record.
     If OPCODE not equal to 'MERG', the data is averaged,
weighted by the data weights.

OPTYPE:
     When MERG mode is specified a problem may arise if the
autocorrelation data have a different averaging time from the
cross-correlation data (common in VLBI experiments). In this
case the YINC will be different for the two sorts of data.
When this occurs you must run UVAVG in MERG mode on the data
twice, setting YINC to the appropriate value for the XC or
AC data and then setting OPTYPE to either 'CROS' or 'AUTO'.
In this case only the relevant data are merged, the other data
type is passed through unscathed.

SORT ORDER:
     The input data base must be in 'BT' or 'TB' sort order.
See above discussion of data set size limitations for 'TB'
sorted data.

EXECUTION TIMES:
     The run time on an otherwise empty VAX 11-785 is

                 3.0 * (D / 100,000) cpu minutes

where D is the number of input UV points.
(This run time is for AVER and may be out of date - RCW)

AIPS