AIPS HELP file for INDXR in 31DEC24
As of Wed Apr 24 19:29:01 2024
INDXR: Task to index a uv data base.
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 #
INFILE Input file for forced scan
breaks
PRTLEV Print level
CPARM -1.0 9999.0 1=> max. time gap (min).
0 => use self-adaptive
method, like other tasks
2=> max scan length (min).
0 => 60 min
3=> CL/CS entry interval in
minutes. 0 => 5 min,
< 0 => don't create a
new table.
4=> VLBA only: recalculate
CL entry group delays
using IM table data.
0 => No recalculation,
1 => Recalculate delays.
5=> VLBA only: recalculate
CL entry atmospheric
group delays and clock
offsets using MC table
data.
0 => No recalculation
1 => Recalculate delays
6=> single-dish only: maximum
"antenna"/"beam" number
in data set (if no AN)
BPARM VLA and EVLA ONLY: Opacity
and Gain-curve control
(see help)
CALIN
Antenna gains file
HELP SECTION
INDXR
Type: Task
Use: Creates an index (NX) table and indexes the uv data file. A
maximum time gap and a maximum scan length may be specified. If
no CL (CS for single-dish data) table is present, an empty one
is (optionally) created. It may be filled with initial
calibration values if desired (CPARM(4) and (5) > 0 for VLBA,
BPARM(1) and (2) >= 0 for VLA). If those initial calibrations
have already been applied, then set CPARM(4)=CPARM(5)=0 and
BPARM(1)=BPARM(2)=-1. Data must be in T* order and may be in
single-source or multi-source format. CL tables are not
created for single-source files. The NX table is used to speed
access to uv data sets by giving offsets into the file for time
ranges, source numbers, and the like. CL and CS tables,
version 1, are the basis for interferometer and single-dish
calibration. Usually they are created as the data are read in
(for the VLA with FILLM, for the VLBA with FITLD, and for some
single-dish data sets with SD2UV) and should not be replaced.
If they are lost or were never created (i.e. OTFUV in OTF 12m
data), then INDXR may be used to create them if they are
needed.
Parameters CPARM(1) and CPARM(2) are particularly important for
single-source files.
For VLA data, options similar to those of FILLM control how a
new CL table is created. Corrections for atmospheric opacity
and/or antenna gain may be inserted into the CL table under
control of BPARM and CALIN. Note that the corrections in the
CL table written by INDXR will be not be identical to those
written by FILLM. This is the result of FILLM having available
correct zenith angles from the VLA model of the Earth, while
INDXR uses a simpler spherical Earth model. The differences in
the gain corrections is rather less than the uncertainties in
the parameters entering the opacity and antenna gain models.
The default opacity model is now based on an algorithm of Josh
Marvel. It uses the older model which mixes surface weather
data with a seasonal model but always evaluates it at K Band.
Then a large table is used to relate the K Band opacity to that
at other frequencies. This allows different opacities for each
IF, while the old method used the same opacity for any IFs
within the same band. The old method is available by setting
BPARM(1) to 100. See EVLA Memo # 143 "Improving the frequency
resolution of the default atmospheric opacity model" by Josh
Marvil (NRAO), 04/06/2010.
For VLBA data, the IM and MC tables may be used to set the
group delays, atmospheric group delays, and clock offsets under
control of CPARM(4) and CPARM(5).
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.
INFILE.....Input file containing lists of times which scan
may not cross (eg. clock setting event times
for space VLBI observations) see explain INDXR
for details.
PRTLEV.....Print level. If PRTLEV > 0 then echo the contents
of INFILE as it is read otherwise read it
silently. Setting PRTLEV > 0 may help in
locating errors in the input file.
CPARM......CPARM(1) = max. gap in data in minutes. If a gap
longer than CPARM(1) is found, a new index
record will be started.
0 => use the routines used by other tasks like UVCOP
to look at the gaps actually in the data to determine
what is likely to be a scan break.
CPARM(2) = max. length (in minutes) of a scan. If
an uninterrupted section of data on the same
source longer than CPARM(2) is found, a new index
record will be started. 0 => 60 min. [For
single-dish data, a "SCAN" random parameter, if
present, will also be used to determine scan
boundaries. In this case, set CPARM(2) to a
high value unless you want to subdivide scans.]
CPARM(3) = interval of CL (CS for single-dish)
table entries in minutes. If there are no CL/CS
tables associated with the data a new one will
be created with null (1's and 0's) entries.
0 => 5 min.
If CPARM(3) < 0, then a new CL or CS table will
not be created.
CPARM(4) = VLBA-only delay recalculation option.
When recreating a CL table, the geometric group
delays used by the VLBA correlator are re-
calculated using information from the IM table.
0 => No recalculation, 1 => recalculate delays.
CPARM(5) = VLBA-only delay recalculation option.
When recreating a CL table, the atmospheric
group delays and the clock offsets are re-
calculated, together with their derivatives,
using information from the model components
(MC) table.
0 => No recalculation, 1 => recalculate delays.
CPARM(6) = single-dish only: the maimum antenna or
beam number actually in the data set. This is
used to cover up for absent antenna (AN) tables
only.
BPARM......Opacity and gain curve control. For non-VLA/EVLA
data, INDXR forces BPARM(1) and BPARM(2) to -1.
Opacity is controlled by BPARM(1) and BPARM(10):
BPARM(1) < 0 -> no opacity correction.
BPARM(1) = 0 -> BPARM(1) = 20
0 < BPARM(1) <= 10 -> opacity correction is done,
with zenith opacity given by BPARM(1).
BPARM(1) > 10 -> opacity correction is done, with
zenith opacity taken as weighted average from
surface weather and seasonal model, with the weight
of the surface weather portion given in BPARM(10),
and the weight of the seasonal model portion given
by 1 - BPARM(10). This requires a weather table.
If it is missing, BPARM(10) will be set to 0 and
the surface weather ignored.
BPARM(1) >= 100 -> same as above but using the old
model where opacities depend only on observing
band rather than being the new, IF-dependent
values. BPARM(1) > 100 may be appropriate for
backwards compatibility, but should not be used
with the EVLA.
BPARM(10) - weight of surface weather model. 0 -> 0.5
If you want 0 set it < 0.
Gain curve is controlled by BPARM(2):
BPARM(2) < 0 -> no gain curve correction.
0 <= BPARM(2) < 2 -> gain curve correction, with
coefficients which vary as a function of band,
frequency (for EVLA), and antenna. These
coefficients are read from a file.
2 <= BPARM(2) < 3 -> gain curve correction, with
coefficients which vary only as a function of band
and, for EVLA only, frequency but not antenna.
These coefficients are read from a file.
BPARM(2) >= 3 -> gain curve correction, with
coefficients specified in BPARM(3), BPARM(4),
BPARM(5), and BPARM(6) for all bands and
antennas.
CALIN......The name of a file to provide the antenna gains used to
populate the initial CL table. If CALIN is left blank,
it defaults to a system file located at:
'AIPSIONS:VLA.GAINS' (old VLA) or
'AIPSIONS:EVLA.GAINS' (EVLA)
The file is in free format with fields: a 1-character
band code, antenna number, begin date in form YYYYMMDD,
end date YYYYMMDD, and 4 gain curve coefficients. The
EVLA file adds a column between band and antenna for the
frequency in MHz.
EXPLAIN SECTION
INDXR: Task to generate index tables
DOCUMENTOR: Chris Flatters
RELATED PROGRAMS: most tasks that handle uv data.
INDXR generates a new index (NX) table for a uv data set and,
optionally, a null calibration table. Records in the NX table are
used to speed access to selected times in the uv data and, in some
programs, to define scan boundaries that cannot be crossed.
Scans are defined independently for each subarray and will
change when either the longest scan or longest gap criteria set
using CPARM are exceeded, when the source ID changes, when the
frequency ID changes, when the scan ID changes or when a time
listed in the file specified as INFILE is encountered.
The external text file is intended to specify times at which
there is potentially some change to the parameters of the
experiment that will affect calibration. The principal example
of such a change is a clock-setting event at a space VLBI ground
station. A clock setting event potentially changes the residual
delay for that station so that it is invalid for a fringe-
fitting solution interval to contain an event.
The file contains a number of blocks each of which specifies
forced scan breaks for a single subarray. Each block begins
with a header that specifies the subarray to which the block
applies and has the form
SUBARRAY = i /
where i is a positive integer.
This is followed by a list of zero or more times specified as
a day of the year and a UTC time. This list should end with
a forward slash.
An example of a complete block would be
SUBARRAY = 1 /
325 14:27:36.765
325 14:32:45.321
/
If there is more than one block for a single subarray then the
times from all of the blocks for that subarray will be combined.
Blocks for subarray that are not present in the data will be
silently ignored.