AIPS HELP file for UVRFI in 31DEC24
As of Wed Apr 24 10:09:29 2024
UVRFI: Task to mitigate RFI at 'BT' (and 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 Smooth or not smoth
amplitudes at the frequency
(channel) axis
smooth(1) = 0 => no smoothing
= 3 => boxcar
smooth(2) width of the boxcar
in channel pixels
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 Use every XINC'th record.
YINC 0.0 Time interval to find
solution (sec), FULLTIME
ZINC 0.0 Time (secs) to which data
were pre-averaged. It must be
close to the true one.
OPCODE algorithm to remove RFI:
'CEXP' - Hogbom clean of fringe
rate spectrum
'CIRC' - fitting the circle
with variable radius
See help
' ' => 'CEXP'
APARM Parameters used in the two
algorithms to remove RFI.
For CEXP:
1 : time interval at the
input data, in sec
2 : Number of pixels
at the fringe rate
spectrum;
0=>1/APARM(1)/2/APARM(3)
3 : Pixel size at fringe
rate spectrum, Hz
<=1/2/FULLTIME
4 : Number of subtracted
complex exponents
0 => 1
5 : number of pixels at the
DM (near 0 fringe rate)
where subtraction is
not allowed to exclude
subtraction of signal
itself.
0 => no limit for
subtraction.
see help
>1/(FULLTIME)/APARM(3)
6 : 0 => 10000
If the flux at given
channel>APARM(6), then
subtraction is allowed
elsewhere,as APARM(5)=0
see help
7 : Gain in the CLEAN
0 => 0.1
8 : Minimum Clean component
FLUX (Jy)
9 : number of pixels at the
DM near the maximum
position found at the
first iteration,
where subtraction is
allowed
10: Number of attempts for
different cleanboxs
0 => 1, see help
For CIRC:
1 : number of iterations
at the NLLSQ algorithm
fitting the circle
0 => 3
2 : 0=> fit the radius
increment
1=> no fit the radius
increment
BADDISK Disks to avoid for scratch
HELP SECTION
UVRFI
Task: This task mitigates RFI using the two algorithm:
'CEXP': Fourier transform of the data at each time interval,
each baseline, each channel,
and following complex Hogbom clean subtracting one or
more components from the "dirty map", using precalculated
"dirty beam". The cleaned value at zero fringe rate is
used for estimation of the actual visibility.
'CIRC': Fitting the circle at the complex visibility plain.
This algorithm is a modernized algorithm of Raman Athrea
ApJ 696, 885, 2009, May 1.
Actually the spiral may be fitted.
The solution for the circle (spiral) center is
used for estimation of the actual visibility.
Adverbs:
INNAME.....Input UV file name (name). Sort 'BT' was tested but code
allows for sort of 'TB' and should now work.
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 considered. ' '=> all; if any starts with
a '-' then all except ANY source named.
QUAL.......Qualifier of source to be considered. -1 => all.
CALCODE....Calibrator code of sources to consider. ' '=> 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.
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.....UVRFI reproduces correct phases but amplitudes still rise
under the expected ones at the frequencies of very high RFI.
The SMOOTH allows to improve the amplitude behavior.
Smooth or not smooth amplitudes at the frequency (channel)
axis
smooth(1) = 0 => no smoothing
= 3 => boxcar
smooth(2) width of the boxcar in channel pixels
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.......Time interval used at the RFI mitigation.
ZINC.......Time (sec) to which data have already been pre-averaged.
UVRFI uses this to estimate the size of the output file.
OPCODE.....algorithm to remove RFI:
'CEXP' - Hogbom clean of the fringe rate spectrum
Fourier transform of the stored time data is carried out.
We call it the Dirty Map (DM)
Fourier transform of the sampling function (Dirty Beam (DB))
is calculated.
The position of the DM maximum of amplitude is found.
The DB located by its maximum at the position of the
maximum of amplitude is multiplied by the value
of the complex DM at this position and subtracted of
the DM. Then such a subtraction is repeated using
the residual. Number of subtraction is given by APARM(4).
Parameters of the set of visibilities and its Fourier
transform are determined by APARMs.
The relations between parameters given by APARM are:
FULLTIME = YINC is the solution interval
APARM(1) = DTIME the time interval in the input data
in sec
APARM(2) is number of points at the half of
the Fourier transform
The range of frequencies at the Fourier
transform is (-0.5/DTIME, 0.5/DTIME)
So maximum value of APARM(2) is
0.5/DTIME / APARM(3)
It may be chosen less if the range of
expected fringe rates is known.
APARM(3) is the step in the Fourier
transform in Hz;
must be <0.5/FULLTIME
APARM(4) is the number of subtracted
complex exponents
APARM(5) is the number of pixels (NPIX) at the
DM (near zero fringe rate) where subtraction
is not allowed to exclude the subtraction of
the signal itself.
It is recommended as =>1/(FULLTIME)/APARM(3)
Example 1:
FULLTIME = 10sec, DTIME = 0.1sec
APARM(1,2,3,4,5)= 0.1 500 0.01 100 10
APARM(6) IF (the channel AMP .GT. APARM(6)) THEN
this channel is considered as RFI,
and the task allows to subtract
at the FOURIER transform elsewhere
including zero fringe rate.
If the found fringe rate period
evaluated at the first iteration appears
to be smaller than half of the solution
interval, then such a channel is flagged.
ELSE
NPIX = APARM(5)
0=> 10000; therefore the flagging is excluded
APARM(7) Gain in the CLEAN
0 => 0.1
APARM(8) Minimum Clean component FLUX (Jy)
APARM(9) number of pixels at the DM (near
the maximum position found at the
first iteration) where subtraction
is allowed
APARM(10) If you think that having finished
the cleaning at the iteration less
the given number of iterations,
the task may continue finding another
(actually only one more) cleanbox.
So the Number of the attempts is
determined by the APARM(10)
Only 2 attempts are allowed.
'CIRC' - fitting the circle with variable radius
In many cases the "circle" looks actually as
a spiral. That is why the fitting of the "circle"
with increment of radius is offered.
The pure circle is the algorithm given by
Ramana Athrea at ApJ, 696, 885, 2009 May 1.
APARM(1) : number of iterations
at the NLLSQ algorithm
of the circle fitting
0 => 3
APARM(2) : 0=> fit the radius increment
1=> no fit the radius increment
'CIRC' works only at special cases, although
it is faster than 'CEXP'.
SO THE 'CEXP' IS MUCH MORE PREFERABLE!!!
' ' => 'CEXP'
BADDISK....The disk numbers to avoid for scratch files (sorting
tables mostly).
EXPLAIN SECTION
UVRFI: Task to mitigate RFI at 'BT' sorted UV data
DOCUMENTOR: L. R. Kogan NRAO/SO
RELATED PROGRAMS: UVAVG
PURPOSE
The UVRFI (opcode='CEXP') mitigates the RFI by Fourier transform of
the time sequence of the visibilities (for each baseline, channel,
polarization and time interval) and following CLEAN of the spectral
(fringe rate) components. The true visibility (from the sky source)
appears at zero frequency, as the result of the fringe stopping
procedure at the correlator. The RFI visibility from the ground
located sources should appear at non zero frequency as the result of
the fringe stopping procedure at the correlator, which shifts the
initial zero fringe rate (the RFI source is immovable relatively the
array). The RFI visibility from a satellite located source should
appear at non zero fringe rate: difference of the fringe rate from the
faster moving satellite and the result of the fringe stopping
procedure at the correlator.
The modify algorithm of Ramana Athrea (ApJ, 696, 885, 2009 May 1)
(opcode='CIRC') fitting the spiral in the Re/Im track (for each
baseline, channel, polarization and each solution time interval) is
available also. 'CEXP' is much more preferable.