AIPS HELP file for KRING in 31DEC24
As of Wed Apr 24 15:19:55 2024
KRING: Task to fringe-fit data
INPUTS
INNAME INPUT UV name (required)
INCLASS class
INSEQ sequence #
INDISK disk #
CALSOUR Select by source name ''=>all
QUAL qualifier -1=>all
CALCODE calcode ''=>all
SELBAND Bandwidth to select (kHz)
SELFREQ Frequency to select (MHz)
FREQID Freq. ID to select < 1=>all
TIMERANG Time range to use 0=>all
BCHAN Lowest channel number 0=>all
ECHAN Highest channel number 0=>all
ANTENNAS Antennas to select 0=>all
DOFIT Antennas to solve for 0=>all
SUBARRAY Subarray 0=>all
UVRANGE Range of uv distance
for full weight 0=>all
WTUV Weight outside UVRANGE 0=>0.0
WEIGHTIT 0.0 3.0 Modify data weights function
DOCALIB -1.0 101.0 > 0 calibrate data & weights
> 99 do NOT calibrate weights
GAINUSE CL table #
DOPOL -1.0 10.0 If >0 correct polarization.
PDVER PD table to apply (DOPOL>0)
BLVER BL table to apply.
FLAGVER FG table #
DOBAND >0 apply BP table
See HELP DOBAND
BPVER BP table #
SMOOTH Spectral smoothing function
See HELP SMOOTH
IN2NAME CLEAN map name (optional)
IN2CLASS class
IN2SEQ sequence #
IN2DISK disk #
INVERS CC table #
NCOMP # CC's/field to use
FLUX CC flux cutoff
NMAPS # Clean map files
CMETHOD Modeling method:
'DFT','GRID',' '
CMODEL Model type: 'COMP','IMAG'
'SUBI' (see HELP re images)
SMODEL Source model, 1=flux,2=x,3=y
See HELP SMODEL
REFANT Reference antenna
SEARCH Fringe search list.
SOLINT Soln. interval (min) 0=>10
SOLSUB Solution subinterval
SOLMIN Min solution interval
SOLTYPE 'NOLS' => do FFT only
'NOFT' => do LS only
other => do FFT + LS
SOLMODE NRD = indep. rates/delays
NR = indep. rates, no delays
ND = indep. delays, no rates
R = one rate, no delays
RD = one rate/mb-delay
RDS = one rate,mb-/sb-delays
RI = one rate/iono-delay
TD = mb-delay + dispersion
default = NRD, see HELP
DOIFS 0.0 64.0 1 => 1 solution for all IFs
2 => 2 solutions, 1 each for
IFs by halves
N => N solutions, 1 each for
NIF/N IFs
0 -> 1 (use 1 for T, S)
SOLMODE must include N to do
each IF individually (DOIFS
is ignored)
OPCODE 'ZRAT' => zero rates
for more, See HELP KRING
CPARM 1 min T_int(sec) 0 => 2
2 delay win(ns) 0 => Nyquist
3 rate win(mH) 0 => Nyquist
4 SNR cutoff 0 => 3
-1 => pass all
5 FFT baseline stacking?
0 => yes
1 => no
6 search to which antennas?
0 => all
1 => only those on SEARCH
list
7 >0 average RR and LL
8 <=0 rereference solutions
9 max SOLINT (min) 0=>10
10 >0 try extrapolation and
reverse traverse
[possibly broken, see HELP]
SNVER Output SN table, 0=>new table
ANTWT Ant. weights (0=>1.0)
BIF First IF included when
when SOLMODE has no N
EIF Last IF included when
when SOLMODE has no N
PRTLEV Print level: 0-> count solns
1-> LS info 2-> FFT info
BADDISK Disk # to avoid for scratch
files.
HELP SECTION
KRING
Task: This task determines phase, rate, and delay corrections
to be applied to a uv data set given a model of the source(s).
The corrections are written to an SN table attached to the
input Multi-Source UV data set.
*** The delay/rate searchs are automatically turned off if less than
two points are available along the corresponding freq/time axes.
*** Plus signs next to the SNR during the FFT stage indicate the
level of baseline stacking used to attain the reported SNR.
SNRs for baselines with differing amounts of stacking should
not be compared!
*** The LS and FFT SNRs now agree with each other for unstacked
data processed one baseline at a time [ostensibly to < 1 percent].
QUESTIONS, COMMENTS? [write to daip@nrao.edu]
[Last documentation overhaul = 20 Oct 1999
[coming one day? - probability of false detection, multiple SN
tables, BL tables...]
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.
CALSOUR....List of sources for which calibration constants are to be
determined, i.e. the calibrator sources All ' ' = all
sources; a "-" before a source name. means all except ANY
source named. Note: solutions for multiple sources can
only be made if the sources are point sources at their
assumed phase center and with the flux densities given in
the source (SU) table.
QUAL.......Only sources with a source qualifier number in the SU table
matching QUAL will be used if QUAL is not -1.
CALCODE....Calibrators may be selected on the basis of the calibrator
code:
' ' => 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
tests, i.e. CALSOUR and QUAL, in the selection of sources
for which to determine solutions.
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 (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 which case the task
will request that you use FREQID.
TIMERANG...Time range of the data to be used. In order: Start day,
hour, min. sec, end day, hour, min. sec. Days relative to
reference date.
BCHAN......First channel to use. 0=>first available.
ECHAN......Highest channel to use. 0=>highest available.
ANTENNAS...A list of the antennas to have solutions determined. If
any number is negative then all antennas listed are NOT to
be used to determine solutions and all others are. 0 =>
0 => use all.
DOFIT......A list of the antennas for which solutions should or
should not be determined. If DOFIT = 0, all antennas are
solved for. If any entry <= -1, , then DOFIT is taken as
the list of antennas for which no solution is desired; a
solution is found for all antennas not in DOFIT. If any
entry of DOFIT is non-zero and all are >= 0, then only
those antennas listed in DOFIT will be solved for - all
other selected antennas will not be solved for.
NOTE: THIS OPTION MUST NOT BE USED UNLESS YOU UNDERSTAND
IT FULLY. Basically, it should be used to solve for the
gains of "poor" antennas after the "good" antennas have
been fully calibrated. Antennas included in ANTENNAS but
not in DOFIT are assumed to have a complex
gain/delay/rate of (1,0,0,0) and the gains/delays
produced will be very wrong if this is not the case.
See HELP DOFIT.
SUBARRAY...Subarray number to use. 0=>all.
UVRANGE....The range of uv distance from the origin in kilowavelengths
over which the data will have full weight; outside of this
annulus in the uv plane the data will be down weighted by a
factor of WTUV.
WTUV.......The weighting factor for data outside of the uv range
defined by UVRANGE.
WEIGHTIT...If > 0, change the data weights by a function of the
weights just before doing the solution. Choices are:
0 - no change weighting by 1/sigma**2
1 - sqrt (wt) weighting by 1/sigma may be more stable
2 - (wt)**0.25
3 - change all weights to 1.0
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 the data.
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 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 three 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 is used to
correct the data.
(c) if DOBAND=3, the table entries are interpolated in time
and the data are then corrected.
BPVER......(multi-source) version of the BP table to be applied.
0 => highest; < 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).
The following specify a CLEAN model to be used if a single source via
specified in CALSOUR:
IN2NAME....Cleaned map name (name). Standard defaults.
Note: a CLEAN image for only a single-source may
be given although it may be in a multi-source file.
If the source table contains a flux, then that flux will
be used to scale the components model to obtain the
stated total flux. This is needed since initial Cleans
may not obtain the full flux even though they represent
all the essentials of the source structure.
IN2CLASS...Cleaned map name (class). Standard defaults.
IN2SEQ.....Cleaned map name (seq. #). 0 -> highest.
IN2DISK....Disk drive # of cleaned map. 0 => any.
INVERS.....CC file version #. 0=> highest numbered version
NCOMP......Number of Clean components to use for the model, one
value per field. If all values are zero, then all
components in all fields are used. If any value is not
zero, then abs(NCOMP(i)) (or fewer depending on FLUX and
negativity) components are used for field i, even if
NCOMP(i) is zero. If any of the NCOMP is less than 0,
then components are only used in each field i up to
abs(NCOMP(i)), FLUX, or the first negative whichever
comes first. If abs(NCOMP(i)) is greater than the number
of components in field i, the actual number is used. For
example
NCOMP = -1,0
says to use one component from field one unless it is
negative or < FLUX and no components from any other
field. This would usually not be desirable.
NCOMP = -1000000
says to use all components from each field up to the
first negative in that field.
NCOMP = -200 100 23 0 300 5
says to use no more than 200 components from field 1, 100
from field 2, 23 from field 3, 300 from field 5, 5 from
field 6 and none from any other field. Fewer are used if
a negative is encountered or the components go below
FLUX.
FLUX.......Only components > FLUX in absolute value are used in the
model.
NMAPS......Number of image files to use for model. For multi-scale
models, set NMAPS = NFIELD * NGAUSS to include the Clean
components of the extended resolutions. If more than one
file is to be used, the NAME, CLASS, DISK and SEQ of the
subsequent image files will be the same as the first file
except that the LAST 3 or 4 characters of the CLASS will
be an increasing sequence above that in IN2CLASS. Thus,
if INCLASS='ICL005', classes 'ICL005' through 'ICLnnn'
or 'ICnnnn', where nnn = 5 + NMAPS - 1 will be used. Old
names (in which the 4'th character is not a number) are
also supported: the last two characters are '01' through
'E7' for fields 2 through 512. In old names, the highest
field number allowed is 512; in new names it is 4096.
CMETHOD....This determines the method used to compute the model
visibility values.
'DFT' uses the direct Fourier transform, this method is
the most accurate.
'GRID' does a gridded-FFT interpolation model computation
' ' allows the program to use the fastest method
CMODEL.....This indicates the type of input model; 'COMP' means that
the input model consists of Clean components, 'IMAG'
indicates that the input model consists of images.
'SUBI' means that the model consists of a sub-image of
the original IMAGR output. If CMODEL is ' ' Clean
components will be used if present and the image if not.
SUBI should work for sub-images made with DO3DIM true and
sib-images of the central facet made with DO3DIM false,
but probably will not work well for shifted facets with
DO3DIM false. Use BLANK rather than SUBIM in such cases.
CALIB will set a scaling factor to correct image units
from JY/BEAM to JY/PIXEL for image models. If the source
table contains a flux, then that flux will be used to
scale the components model to obtain the stated total
flux. This is needed since initial Cleans may not obtain
the full flux even though they represent all the
essentials of the source structure.
SMODEL.....A single component model to be used instead of a CLEAN
components model; if abs (SMODEL) > 0 then use of this
model is requested.
SMODEL(1) = flux density (Jy)
SMODEL(2) = X offset in sky (arcsec)
SMODEL(3) = Y offset in sky (arcsec)
SMODEL(4) = Model type:
0 => point model
1 => elliptical Gaussian and
SMODEL(5) = major axis size (arcsec)
SMODEL(6) = minor axis size (arcsec)
SMODEL(7) = P. A. of major axis (degrees)
2 => uniform sphere and
SMODEL(5) = radius (arcsec)
The following control how the solutions are done, if you don't
understand what a parameter means leave it 0 and you will probably get
what you want.
REFANT.....The desired reference antenna for phases. Note that
the desired refant is not required to be the primary search
antenna. You should choose the REFANT to be an antenna
that is present during most of the observation.
SEARCH.....List of prioritized reference antennas to be used for
fringe searching during the FFT stage. KRING constructs
an internal search list to determine the order in which to
perform the FFTs. This search list is constructed by first
copying the elements of SEARCH. Finally, all remaining
antennas antennas are appended to the search list in
numerical order. You can limit the search to only the
specified elements of the SEARCH list by setting CPARM(6).
Only baselines where at least one antenna appears in the
search list will be searched for fringes.
You should explicitly order the antennas in terms of decreasing
sensitivity if at all possible.
SOLINT.....The solution interval. Note that this is only a
recommended solution interval. The actual solution interval
used by KRING will be changed in order to divide each scan
evenly into an integral number of data chunks.
SOLINT is in minutes; the default value (SOLINT=0) is 10
minutes. SOLINT values larger than 10 are reset to 10 minutes
unless CPARM(9)>0. NB: If SOLINT > 0.75*Scan, SOLINT = Scan.
SOLSUB.....The begin time for the next interval in advanced from the
current one by SOLINT / SOLSUB where 1 <= SOLSUB <= 10.
0 -> 1. This is to produce solutions at sub-intervals of
SOLINT based on SOLINT length of averaging.
SOLMIN.....Minimum number of subintervals to be used in a solution.
0 -> SOLSUB.
SOLTYPE....If 'NOLS', only a FFT delay/rate search is performed.
If 'NOFT', only a LS delay/rate search is performed.
Otherwise, a FFT search is followed by a Least Squares search.
SOLMODE....This four character string controls the types of parameters
to be solved for. In any order, the following may be
specified:
N -> solve for N sets of quantities [ per IF ]
*** see DOIFS for solutions spanning > 1 IF.***
R -> solve for rate [ per IF or
only one common to all IFs ]
D -> solve for delay [ per IF (single band delays) or
only one (multi-band delay) ]
S -> solve for stair-step delay [ only one, usually only
needed for MkIII data
where pulse-cals have
been used ]
I -> solve for an ionospheric delay [ only one, approx.
proportional to
inverse frequency ]
T -> solve for an ionospheric delay [ only one, exactly
proportional to
inverse frequency ]
4,2, or 1 -> use a factor of 4,2, or 1 of zero padding in the
FFTs.[use 4,2, or 1 for speed over accuracy]
*** If N is specified, I,S,T are ignored.
[T also stores the ionosphere in the mb-delay column
so you can see the solved for values using SNPLT.
The actual phase/delay solutions stored using I or T
are identical.]
*** Phases are always solved for***
Commonly encountered modes would be:
NRD = APARM(5)=0 in FRING
RD = APARM(5)=1 in FRING
RDS = APARM(5)=2 in FRING
ND, D, DS = same as NRD, RD, and RDS respectively but
do not solve for rates
NR, R = same as NRD and RD, respectively but
do not solve for any type of delays
Default is NRD .
*** Note Bene, SOLMOD = 'ND' is different from
SOLMOD = 'NRD', OPCODE='ZRAT' . The latter
first determines the best fitting rate along
with other solutions and then zeroes the rate
solution in the final SN table - this is usually
what you want.
DOIFS......If DOIFS is set to N, then determine N solutions using
NIF/N IFs in each one. Note that NIF must be an integer
multiple of N or the task will quit. The default is 1
but will be set to 0 (separate solutions for each IF if
SOLMODE contains an 'N').
OPCODE.....Solution masking to be performed _after_ fringe-fitting
' ' no masking
'ZPHS' zero phases in output SN table
'ZRAT' zero rates in output SN table
'ZDEL' zero delays in output SN table
If CPARM(8)>0, OPCODE is forced = ' '.
CPARM(1)...The minimum integration time of the data (sec);
0 => 2 'VLBA' seconds
It is important to get this number right to within 20 percent.
E.g., if you've averaged up 1 second data to 10 seconds,
setting this to 10 is okay so long as there are only a
very few points with shorter than 10 second integration
times. If you set this to 1 second, you will regret it.
CPARM(2)...The delay window FW to search (nsec) centered on 0 delay.
<= 0 => full Nyquist range.
[Use SOLMOD to turn off the delay search.]
CPARM(3)...The rate window FW to search (mHz) centered on 0 rate.
<= 0 => full Nyquist range.
[Use SOLMOD to turn off the rate search.]
CPARM(4)...The minimum allowed signal-to-noise ratio. <0 => 3
The SNR calculation is described in AIPS Memo 101.
[You might consider setting this to 5.]
CPARM(5)...Number of baseline combinations to use in the initial,
FFT fringe-search (1-3). Larger values increase the
point source sensitivity but reduce the sensitivity to
extended sources when an accurate model is not available.
0=>3.
[Solutions formed using combinations of baselines are
marked with a plus for singly indirect combinations and
with two pluses for doubly indirect combinations.]
CPARM(6)...If CPARM(6)=1, only baselines to those antennas on the
SEARCH list are searched during the FFT stage. Otherwise,
other baselines are eventually searched until either fringes
have been found to each antenna, or no baselines remain to
be searched.
CPARM(7)...If >0, RR and LL data are averaged together and only a
single solution is determined for both polarizations. This
is useful when reducing polarization data.
CPARM(8)...If <= 0 then the phase, rate and delays will be
re-referenced to a common antenna. CPARM(8)=1 is only
desirable for VLBI polarization data. Using this option also
forces OPCODE = ' '.
CPARM(9)...If SOLINT>10 is desired, you must set CPARM(9)>0 . This
is necessary to prevent accidentally requesting more memory
than your computer can deliver and locking up computer.
CPARM(10)..Try Hard Option. If CPARM(10)>=0, When KRING is ready to
do the initial FFT-based fringe search, it will first try
to initialize residual fringe-fit delay and rate solns for
each antenna using an average of all good solutions found
in the SN table. Only those antennas for which acceptable
solutions are not found will then be FFTd to find fringes.
This does not preclude the final Least Squares refinement.
[20 Oct 1999, it has been reported that CPARM(10) is broken -
it may trash the solutions - dont try it unless you have
the time to re-run KRING if need-be.]
SNVER......Desired output SN table. Solutions will be added to the
specified table replacing any previous solutions for the
same TIMERANG, CALSOUR etc. 0 means create a new SN table.
ANTWT......Antenna weights. These are additional weights to be
applied to the data before doing the solutions, one per
antenna. Use PRTAN to determine which antenna numbers
correspond to which antennas. This really is unnecessary
in most cases now.
BIF........First IF included when when SOLMODE does not contain an
N (all IFs receive the solution found for the appropriate
group of IFs, but only BIF-EIF are used to find it).
EIF........Last IF included when when SOLMODE does not contain an
N (all IFs receive the solution found for the appropriate
group of IFs, but only BIF-EIF are used to find it).
PRTLEV.....Print flag,
0=minimal - (almost nothing).
1 = LS solution information + scan information
2 = FFT solution information
3 = nothing really new.
>3, all kinds of debugging info.
BADDISK....A list of disk numbers to be avoided when creating scratch
files.
EXPLAIN SECTION
KRING - who wrote it? ? who rewrote it? kdesai@nrao.edu
KRING - documentation? - kdesai@nrao.edu [with input from mrupen@nrao.edu]
KRING - currently maintained by? - kdesai@nrao.edu
need help? - daip@nrao.edu
For some basic introduction to fringe-fitting, please see the discussions
in:
Chapter 9 of Interferometry and Synthesis in Radio Astronomy,
AR Thompson, JM Moran, & GW Swenson Jr., Krieger Publishing, 1991
Global Fringe Search Techniques for VLBI,
FR Schwab, WD Cotton, AJ, 88, 5, 1983
The Calculation of SNR in KRING's FFT stage,
KM Desai, AIPS MEMO 101, 1998
The AIPS cookbook also describes how and when KRING should be used.
Brief description:
KRING is a rewrite of the AIPS fringe-fitting task FRING.
BLING/BLAPP is an alternate method of fringe-fitting in AIPS.
These tasks all implement in one way or another the global fringe-
fitting algorithm described in Schwab and Cotton.
KRING differences from FRING:
MEMORY USAGE:
-KRING uses up to a third less memory for full Nyquist window
searches and can save even more if smaller search windows are
specified.
-KRING uses an indexing scheme to track the integration times on
different baselines. This scheme has its weaknesses [it does not
gracefully handle the case when the integration times are not all
multiples of the shortest integration time] but in most data sets
now produced by the VLBA correlator, uses (N-2)*(N-1)* T_int_max /
(2 * T_int_min) less memory [N is the number of stations in the
data set].
SCRATCH FILE USAGE:
-FRING creates a scratch file consisting of calibrated _uncompressed_
data. If a complicated source model is used, this scratch file is
potentially _SIX_ times bigger than the original [compressed] data
set.
KRING requires an NX table and creates scratch files for one scan at
a time. This results in much smaller scratch file usage at the cost
of some overhead to create each scratch files. This is a noticeable
penalty when fringe-fitting phase-referenced observations.
Currently, the scratch file grows as longer scans are found
but does not shrink when shorter scans are encountered.
SOLUTION INTERVALS:
KRING uses a different scan-breaking algorithm to try to make all
solutions in a scan the same length - this algorithm may be more
robust than FRING when: the user asks for one solution per scan, the
TIMERANG is set.
RESTRICTED DELAY/RATE SEARCHES
KRING implements delay and rate searching more uniformly so that the
options to turn off delay or rate searches now work- previously it was
difficult to turn off the rate search.
SOLUTION EXTRAPOLATION and REVERSE TRAVERSE
KRING can try to extrapolate solutions from previously found
solutions. Before doing an FFT, KRING will check if the average of
all previously found solutions has an SNR larger than the cutoff.
If so, the delay and rate are adopted and a new phase solution is
computed. If the average solution's SNR is too low, KRING
falls back to doing the FFT. This can be expensive for data of
uniformly poor quality of with uniformly weak fringes and should be
turned not be used in such cases. This option is off by default.
[20 Oct 99, it has been reported that CPARM(10) is broken, I don't
recommend its use until further notice. Sorry for the
inconvenience!]
SNR CALCULATIONS:
The SNR calculation in KRING is based upon an analytical expression
for the SNR that can be found in AIPS memo 101. Note that the SNR
calculations from the LS and FT stages are only expected to agree
when processing one baseline at a time [but, in that case, they are
expected to agree to within 1 percent].