AIPS HELP file for VLBAAMP in 31DEC22
As of Thu Jun 30 1:49:21 2022
VLBAAMP: Applies a-priori amplitude corrections
INPUTS
INNAME Input file name
INCLASS Input file class
INSEQ Input file sequence number
INDISK Disk number for input file
SUBARRAY Subarray to correct. 0=>ALL
ICHANSEL Array of start and stop chn
numbers, plus a channel
increment and IF to be used
for channel selection in the
averaging in ACSCL.
Default = central 75 percent of band
DOFIT Fit for opacity correction
BADDISK Disks to avoid for scratch
VLBAAMP is defined in the VLBAUTIL run file.
HELP SECTION
VLBAAMP
Type: Procedure
Use: VLBAAMP is a procedure that applies post-bandpass and delay
calibration amplitude correction and a-priori amplitude corrections.
These corrections are added to the corrections in the highest
numbered CL table.
VLBAAMP assumes that you already have GC and TY tables and that you
have at least one CL table.
Type RUN VLBAUTIL to define the VLBAAMP procedure.
INNAME.....The name of the file to be corrected. Wildcard characters are
allowed.
INCLASS....The class of the file to be corrected. Wildcard characters are
allowed.
INSEQ......The sequence number of the file to be corrected. Zero defaults
to the highest sequence number of a file matching INNAME,
INCLASS, and INDISK.
INDISK.....The disk drive number of the file to be corrected. Zero defaults
to any disk.
SUBARRAY...The subarray to correct. Zero defaults to doing all.
ICHANSEL...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.
DOFIT......Do opacity correction in APCAL. This is recommended
for high frequency experiments (freq >= 15~GHz) if the
accuray of the source flux is important.
BADDISK....A list of disks on which scratch files are not to
be placed. This will not affect the output file.
EXPLAIN SECTION
VLBAAMP: Procedure to apply a-priori amplitude corrections
Documentor: Amy Mioduszewski
Related Programs: VLBAUTIL, ACSCL, SNSMO, APCAL, CLCAL
VLBAAMP determines the post-bandpass and delay calibration amplitude
correction and a-priori amplitude corrections from the gain curves and
system temperature measurements, and applies these corrections to the
highest numbered calibration (CL) table attached to the input file.
Note that interpolation type 'SELF' is used for the a-priori amplitude
calibration, to avoid interpolating between sources at different
elevations, among other things.
You should run VLBAAMP after loading any gain curves or system temperature
data for non-VLBA antennas using ANTAB.
VLBAAMP should be used along with (and after) VLBAACOR and VLBABPSS instead
of VLBACALA. This redesign of the amplitude calibration path is based on
VLBA Scientific Memo #37 (Craig Walker). VLBAAMP should NEVER be used with
VLBACALA. The new recommended steps for amplitude calibration are:
1) Do preliminary calibration steps that are necessary (e.g., VLBAFIX,
VLBAEOPS, VLBATECR...).
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.
ICHANSEL defaults to the inner 75 percent of each IF in ACSCL. That is a good
deafult for the older PFB backend of the VLBA. The inner 89 percent could be
used for the more modern DDC backend but this difference should not
matter much. The more general advice would be to set it to the channels
you intend to use for imaging.