AIPS NRAO AIPS HELP file for AVSPC in 31DEC18



As of Mon Apr 23 7:19:18 2018


AVSPC: Task to average uv data in frequency.

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
STOKES                             Stokes of output
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
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 #.
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.
AVOPTION                           Averaging option '  ','SUBS'
                                   SUBS ignores ICHANSEL.
CHANNEL                            # chans to average together
                                   used when AVOPTION = 'SUBS'

HELP SECTION

AVSPC
Task: Average a uv database in the frequency domain.  The two
      principal uses of this task are to create a data base containing
      'continuum' channels for use in calibrating spectral line
      observations and for averaging in frequency for continuum
      observations that don't require frequency resolution to reduce
      bandwidth smearing.

      For the purpose of forming a continuum data base from spectral
      line observations AVSPC has optional channel selection so
      channels may be omitted from the average if necessary.  The
      default channel range that is averaged is the center 75 percent, this
      is what is used at the VLA to produce 'channel 0'.

      Note that there are other tasks for forming channel 0 data sets
      and for frequency averaging including averaging over IFs.  These
      include SPLIT and SPLAT, UVLSF which fits a linear continuum to
      a (possibly shifted) spectrum, and SPECR which uses Fourier
      transform methods to increase or decrease the number of spectral
      channels.
Adverbs:
  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.
  SOURCES....Source to be included.   '  '=> all; if any starts with
             a '-' then all except ANY source named.
  QUAL.......Qualifier of source to be included. -1 => all.
  CALCODE....Calibrator code of sources to include. ' '=> all.
  STOKES.....Specifies which STOKES parameters are written in the
             output data set:  ' ' => 'FULL'
               'I','Q','U','V', 'IV', 'IQU', 'IQUV'
               'RR','LL', 'RL', 'LR', 'RRLL', 'RLLR', 'RLRL'
               'XX','YY', 'XY', 'YX', 'XXYY', 'XYYX', 'XYXY'
             'HALF', 'CROS', and 'FULL' have sensible interpretations
             depending on the Stokes present in the data.  The last in
             each of the 3 rows above == 'FULL'.  Note that many
             combinations of polarizations in the input and values
             above are not supported.
  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.
             Channel selection is done with ICHANSEL.
  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).
  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.
  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.
             IMAGR uses DOBAND as the nearest integer; 0.1 is therefore
             "false".
  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. #).   0 => highest unique
  OUTDISK....Disk drive # of output UV file. 0 => highest with
             space for the file.
  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.
  AVOPTION...The averaging option.
             '    ' means only average frequency channels for each IF
                separately under control of ICHANSEL.
             'SUBS' means average every n channels of each IF together
                ignoring ICHANSEL producing an output file of spectral
                size INT(input/n). Any excess channels from the input
                spectrum will be discarded. The number of channels to
                average together is specified by CHANNEL. E.g.
                AVOPTION = 'SUBS', CHANNEL = 8 on a 128 channel input
                file will produce 16 channels in the output file. The
                ICHANSEL adverb is ignored when AVOPTION = 'SUBS'  A
                boxcar average will be done of those channels to be
                averaged together.
  CHANNEL....The number of channels/IF to average together when
             AVOPTION = 'SUBS'.
             i.e., channel = # input channels / # output channels

EXPLAIN SECTION


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