AIPS HELP file for XYDIF in 31DEC24
As of Wed Apr 24 8:24:46 2024
XYDIF: Task to return/apply X - Y linear pol. phase difference
INPUTS
INNAME UV data (name).
INCLASS UV data (class).
INSEQ 0.0 9999.0 UV data (seq. #). 0 => high
INDISK Disk unit #. 0 => any
CALSOUR Calibration source list
CALCODE Calibrator code ' '=>all
TIMERANG Time range to list
SELBAND Bandwidth to select (kHz)
SELFREQ Frequency to select (MHz)
FREQID Freq. ID to select.
None selected => 1.
BIF 0.0 100.0 Lowest IF number 0=1
EIF 0.0 100.0 Highest IF number
BCHAN 0.0 2048.0 Low channel number 0=>1
ECHAN 0.0 2048.0 High channel number
ANTENNAS Antennas to list
UVRANGE 0.0 UV range in kilolambda
SUBARRAY 0.0 1000.0 Subarray, 0=>1
Cal. info for input:
DOCALIB -1.0 101.0 > 0 calibrate data & weights
> 99 do NOT calibrate weights
GAINUSE CAL (CL or SN) table to apply
DOPOL -1.0 10.0 If >0 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 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.
DOINVERS -1.0 1.0 > 0 -> add 180 to solutions
SOLINT Averaging time in minutes
DOKEEP -1.0 1.0 > 0 => keep the solution
for every SOLINT interval
in the PP table
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.
DOAPPLY -1.0 1.0 > 0 => apply to CL or BP
table now
SPECTRAL -1.0 1.0 > 0 do spectral solution
using PD table
INTPARM Smoothing parameters for
spectral mode
DOPRINT -3.0 132.0 > 0 -> use the terminal,
else use the line printer
> 72 => terminal width
= 0 -> no printing
OUTPRINT
Printer disk file to save
BADDISK Disk to avoid for scratch.
CLCORPRM @ X-Y phase difference returned
if SPECTRAL <= 0
HELP SECTION
XYDIF
Type: Task
Use: Determines the X minus Y linear polarization phase difference
by comparing the phases of the U and V Stokes visibilities in
the frame of the antenna rather than the source. The phase
difference is ATAN2 (V,U), as a function of IF and/or spectral
channel. Note that this phase difference arises because the
X and Y phases are separately referenced with nothing in CALIB
and BPASS to force the two to a common reference. Note that
this function requires a linearly polarized source with no
circular polarization. The phase difference causes U to rotate
into V.
XYDIF can be run in an IF-dependent fashion (SPECTRAL <= 0).
In this mode, it can print matrix listings of U and V which
can be examined for bad data and/or other issues. XYDIF
returns the mean phases in the CLCORPRM adverb. Unlike RLDIF,
these values need no correction before they are used in CLCOR.
The printing in XYDIF may be suppressed. Set DOAPPLY=1 for
this. A new CL table is created.
XYDIF may also be used in a fully channel-dependent mode
(SPECTRAL > 0). In this mode, the matrix printing is
suppressed, but the answers and rmses may be (should be)
printed. If DOAPPLY > 0, the BP table is corrected, with a new
version being written.
The RMSes printed are meant to be the uncertainties in the mean
values.
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.
CALSOUR....List of calibration sources to be used. ' '=> all; if
any starts with a '-' then all except ANY source named.
CALCODE....Calibrators may be selected on the basis of the
calibrator code given in the SU table.
' ' => any calibrator code selected
'* ' => any non blank code (cal. only)
'-CAL' => blank codes only (no calibrators)
anything else = calibrator code to select.
NB: The CALCODE test is applied in addition to the
other selection tests
TIMERANG...Time range of the data to be used and listed. In order:
Start day, hour, min. sec,
end day, hour, min. sec.
Days relative to reference 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, 0=> all
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, 0=> all
FREQID.....Frequency identifier to select. If either SELBAND or
SELFREQ are set, their values overide that of FREQID.
However, setting SELBAND and SELFREQ may result in an
ambiguity. In that case the task will request that you
use FREQID. If neither SELBAND, SELFREQ nor FREQID are
specified then the first FQ id in the FQ table (usually
1) will be used.
BIF........IF to list - first returned. 0 -> 1
EIF........Last IF listed and returned. 0 -> BIF+19 or max
whichever is smaller.
BCHAN......First channel to average. 0=> 1
When SPECTRAL > 0, channels < BCHAN are corrected but
using smoothed corrections from channels BCHAN and
greater. All channels are used to find solutions
however.
ECHAN......Last channel to average. 0=> Highest
When SPECTRAL > 0, all channels are used to find
solutions. However, the corrections for channels > ECHAN
are determined by the solutions for channels <= ECHAN.
ANTENNAS...A list of the antennas to list. If any number is
negative then the antennas specified are not listed
and all others are. All 0 => list all.
UVRANGE....Range of projected spacings to be listed in 1000's of
wavelengths. 0 => 1, 1.E10
SUBARRAY...Subarray number to list. 0=>1.
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 Cal. table to apply to the
data if DOCALIB=1. Refers to a CL table for
multisource data of an SN table for single source.
0 => highest. Used for OPTYPE='MATX','LIST'.
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 appply. <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.
BPVER......Specifies the version of the BP table to be applied.
<0 => no bandpass correction done.
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).
DOINVERS...False (<= 0) => use basic solution with function ATAN
True (> 0) => add 180 degrees to basic solution - this
option is present for debugging purposes only. Use
it with care!
SOLINT.....Averaging time in minutes. 0 => scan for multi-source
files, 10 minutes for single-source files. Does not
average beyond scan boundaries in either case.
DOKEEP.....> 0 => the solution for every time (SOLINT) interval is
written to the PP table records 2 -> N+1 where
N is the total number of such intervals. The final
average is written to record 1.
<= 0 => the PP table contains only one record, the average
result.
ICHANSEL...When DOKEEP > 0 and there is more than one solution
interval the various solutions are averaged and compared
to the global average solution to write IF-dependent
phase differences to a new SN table.
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.
DOAPPLY....False (<= 0) => pass the results back to AIPS in CLCORPRM
if SPECTRAL is false and display results in the
message window.
True (> 0) => copy the GAINUSE CL table to the
highest+1 and correct the L phases (when SPECTRAL
is false). Otherwise, copy the BPVER bandpass
table and apply the L phases when SPECTRAL is
true.
SPECTRAL...False (<= 0) => average spectral channels BCHAN tthrough
ECHAN and apply the solution through the CL table
or CLCORPRM on an IF basis.
True (> 0) => find the R-L phase difference on a
channel by channel basis and, if DOAPPLY > 0, apply
the result through the BP table. DOPRINT and
OUTPRINT allow a text file suitable for plotting to
be produced.
INTPARM....After the phase corrections are determined, they may be
smoothed in frequency further using the INTPARM selected
function. This is to provide better S/N than one would
have with unsmoothed single channels.
INTPARM(1) = type of smoothing to apply:
0 => no smoothing
1 => Hanning
2 => Gaussian
3 => Boxcar
4 => Sinc (i.e. sin(x)/x)
INTPARM(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 INTPARM(1) =
1 - 4.
INTPARM(3) = the diameter over which the convolving
function has value - in channels. Defaults: 1, 3, 1, 4
times INTPARM(2) used when input INTPARM(3) <
INTPARM(2) (after application of defaults).
To avoid spectral shifts, all functions are applied
symmetrically. Boxcar of width "2" actually does 3
channels averaging, for example, channels 9, 10, and 11
for output channel 10. Width 3 does the same. Width 4
is needed to include channels 8 and 12. This is different
than boxcar with SMOOTH.
DOPRINT....For DOLINE <= 0, the printing option is for MATX
LISTR-like displays of RL and LR* phases with rmses under
control:
False (< 0) use the line printer if OUTPRINT = ' '
else write named OUTPRINT file only.
When OUTPRINT is not blank, DOPRINT=-2 suppresses
the page-feed character on page headers and
DOPRINT=-3 suppresses page headers and most other
header information.
= 0 no printing just return answer.
True (> 0) use the terminal interactively. The task
will use the actual terminal width as a display
limit unless 72 < DOPRINT < width. In that case, the
display limit will be DOPRINT characters.
For DOLINE > 0, any DOPRINT not equal 0 will cause a text
file to be written to OUTPRINT if that adverb is not
blank. This text file will be suitable input to PLOTR.
If DOPRINT > 0, this file contains separate lists for each
source and excludes channels outside BCHAN and ECHAN.
If DOPRINT < 0, the smoothed and extrapolated and averaged
over sources correction data are shown instead.
OUTPRINT...For DOLINE <= 0, disk file name in which to save the line
printer output. ' ' => use scratch and print
immediately for interactive jobs - batch jobs use
OUTPRINT = 'PRTFIL:BATCHjjj.nnn' (jjj= job #, nnn =
user #). When OUTPRINT is not blank, multiple outputs
are concatenated, and the file is not actually
printed.
For DOLINE > 0, if not ' ', the disk file name of a file
to contain a text file which, when fed to PLOTR, can
make a plot of the spectrum of the corrections.
BADDISK....Disk numbers to avoid for scratch files. Scratch
files may be created by the sorting routines if
calibration or flagging is applied.
CLCORPRM...OUTPUT adverb: X-Y phase difference in degrees for IFs
BIF through BIF+19. The self-consistent mean phases so
determined are returned in the adverb CLCORPRM.
EXPLAIN SECTION