AIPS HELP file for AVSPC in 31DEC24
As of Fri Apr 26 7:51:47 2024
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'
BADDISK Disks to avoid for scratch
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'
'VV','HH', 'VH', 'HV', 'VVHH', 'VHHV', 'VHVH'
'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
BADDISK....The disk numbers to avoid for scratch files (sorting
tables mostly).
EXPLAIN SECTION