AIPS HELP file for VLBABPSS in 31DEC22
As of Fri Jun 2 12:56:16 2023
VLBABPSS: Procedure to create BP table
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 #
CALSOUR Bandpass calibrator sources.
CALCODE Calibrator code ' '=>all
TIMERANG Time range to select
ANTENNAS Antennas to select
CLEAN map (optional)
IN2NAME Cleaned map name (name)
IN2CLASS Cleaned map name (class)
IN2SEQ 0.0 9999.0 Cleaned map name (seq. #)
IN2DISK 0.0 9.0 Cleaned map disk unit #
INVERS -1.0 46655.0 CC file version #.
NCOMP # comps to use for model.
1 value per field
FLUX Lowest CC component used.
NMAPS 0.0 4096.0 No. Clean map files
CMODEL Model type: 'COMP','IMAG'
'SUBI' (see HELP re images)
SMODEL Source model, 1=flux,2=x,3=y
See HELP SMODEL for details.
REFANT Reference antenna
BPASS5 If not 0, set BPASSPRM(5) =
BPASS5 ELSE SET IT 1.
See help for details.
VLBABPSS is defined in the VLBAUTIL run file.
Use: VLBABPSS runs BPASS for VLBA data.
This procedure is based on the recommendations laid out in VLBA
Scientific Memo #37 (Craig Walker). Run VLBAAMP after VLBABPSS.
That procedure begins by running ACSCL to perform post-bandpass
and delay amplitude corrections. It then does the a-priori
amplitude corrections with APCAL.
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 bandpass response functions are
to be determined. All ' ' = all sources; a "-" before a
source name means all except ANY source named. If the data
file is a single-source file no source name need be
specified. If both IN2NAME and IN2CLASS are specified,
but multiple sources are selected, BPASS will quit.
CALCODE....Calibrators may be selected on the basis of the calibrator
' ' => 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.
TIMERANG...Time range of the data to be selected. In order: Start day,
hour, min. sec, end day, hour, min. sec. Days relative to
ANTENNAS...A list of the antennas for which bandpasses are to be
determined. If any number is negative then all antennas
listed are NOT to be used and all others are.
The following specify a CLEAN model to be used if a single source was
specified in CALSOUR
IN2NAME....Cleaned map name (name). ' ' => no Clean model
Note: a CLEAN image for only a single source may be given
although the uv data 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). ' ' => no Clean model
If a Clean model is specified, then only one source may
be selected (multi-source files) and no SMODEL may be
specified (single-source files).
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
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.......Only components > FLUX in absolute value are used in the
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
' ' allows the program to use the fastest
NOTE: when using a model derived from data with
different uv sampling it is best to use 'DFT'
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.....For single-source files only: a single component model to
be used instead of a CLEAN components model; if SMODEL(1)
> 0 then use of this model is requested. Note that
IN2NAME or IN2CLASS must be blank if SMODEL(1) > 0 and
both must be specified if SMODEL(1) <= 0 for
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)
REFANT.....The antenna to use as a reference in the least-squares
BPASS5.....If 0, BPASSPRM(5) = 1. If not zero, BPASSPRM(5)=BPASS5.
HELP BPASS says:
(5) Divide by channel 0 option. *** CHANGED MAY 2010 ***
In general, use 0.1 when using multiple calibration
sources. ICHANSEL default is inner 75 percent.
If ~0 (-0.5 to 0.5,but not 0) the value of "channel
0" is determined and applied (divided into the data)
on a record-by-record basis, either from the average
of channels specified by ICHANSEL or from an external
file (if IN3NAME and IN3CLASS are specified). If
-1 (-1.5 to -0.5), the same is done but the
amplitude of channel 0 is made 1.0 so a phase-only
correction is made. Note that model division is
turned off if either of these options is selected.
If -2 (< -1.5), divide by the average of channels
specified by ICHANSEL (no external file) after the
time averaging. This option allows a normalized
bandpass to be found correcting for any
uncalibrated variations in the continuum. If you
have poor phase stability use 0 or -1, if you have
decent phase stability use -2.
If you have good phase stablility use +1. Note
that division by channel 0 adds biased noise
because the channel-averaged amplitude is by its
very nature biased; the -2 option should be less
biased since the data have been vector averaged in
time first and so are less noisy. The -1 (phase
only) division should avoid the amplitude bias but
then the banddpasses are not normalized. That can
be corrected later with BPASSPRM(10) options.
If > 0.5, do no normalization before determining the
solutions. This requires good stability during
each integration period. BPASSP(10)=3 still allows
a normalized solution which may be even less biased
since it is on an antenna rather than a baseline
Note also that a channel 0 may not be determined
sensibly if the phase changes a lot across the pass
band except by setting ICHANSEL to select a very few
******** Note, if normalization is not done on a
record-by-record basis, users must be very careful
about averaging different calibration sources. Any
channel-dependent flagging will cause the different
sources to be differently weighted in the partly
flagged channels than in the completely unflagged
ones. The shape of the bandpass in this case will
not be correct. Therefore, if channel-dependent
flagging is done and multiple calibrators averaged,
the normalization must be done on a record basis.
VLBABPSS: Procedure to determine antenna bandpass functions from
Documentor: Amy Mioduszewski
Related Programs: BPASS
This procedure is defined in VLBAUTIL.
VLBABPSS determines the bandpass calibration using BPASS.
VLBABPSS should be used along with VLBACCIR and VLBAAMP instead of
VLBACALA. This redesign of the amplitude calibration path is based on
VLBA Scientific Memo #37 (Craig Walker). The new recommended steps for
amplitude calibration are:
1) Do preliminary calibration steps that are necessary (e.g., VLBAFIX,
2) VLBACCOR -- digital sampling corrections
3) VLBAMPCL (or VLBAPCOR) -- remove instrumental delay
4) VLBABPSS -- do bandpass
5) VLBAAMP -- correct auto-correlations and a priori amplitude calibration
6) Continue with calibration.