AIPS HELP file for VLANT in 31DEC22
As of Sat Dec 2 8:22:25 2023
VLANT: Task to apply VLA antenna position corrections from OPs
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 #
SUBARRAY 0.0 Input subarray = AN file
GAINVER Input CL table 0=>high
DOINVERS -1.0 1.0 > 0 => undo the correction
VCODE 'NOAN' do not do antenna corr
'NOEL' do not do atm delay
else do both
DETIME 0.0 Do not include changes more
than DETIME years after obs
0 -> 10.0
Task: This task determines the antenna position corrections applied
by the VLA operations staff after your observation that apply
to that observation. It copies an input CL table and applies
these antenna position corrections to the antenna phases.
WARNING: THIS TASK WILL CHANGE THE ANTENNA TABLE. Careful
observers might wish to make a copy of the AN table (e.g. with
TASAV) before running VLANT. Note the DOINVERS option added
to allow the change to the AN table to be undone. The undo
also applies to the CL table so be careful with GAINVER.
This task works with data from the VLA Correlator through
January 2010 and for the EVLA correlator thereafter. Note that
the coordinate system used in the two environments is
different, so the numbers in the tables are different. The
two environments therefore use files by slightly different
Moving sources (e.g. planets) are supported when there is a PO
VLANT now also applies corrections to the CL table for an error
in the atmospheric delay present in the EVLA on-line system
from IAT date August 9, 2016 to November 15, 2016. The
correction will be applied automatically if your data are
affected and will be skipped iF your data do not fall in this
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.
SUBARRAY...Which subarray to correct. This selects the AN table
that will be considered and updated.
GAINVER....Input CL table version. If GAINVER is equal zero or
greater than the total number of the CL tables
then GAINVER is equal to the last existing CL table.
A new CL table will always be created if any corrections
VCODE......'NOAN' says to do the atmospheric delay correction if
appropriate but to do no antenna position
'NOEL' says the opposite
else do both when appropriate
DETIME.....Do not include antenna corrections more than DETIME years
after the observation. 0 -> 10.
The EVLA atmospheric delay correction formula from Barry Clark
DELAY = D * cot(el)*csc(el) * cos(Az_o - Az_a) * E_t
where f is the frequency of that channel
D is the distance from the array center to the antenna
el is the elevation of the observation
Az_o is the azimuth of the observation
Az_a is the azimuth of the arm the antenna is on
E_t is the error term as tabulated below (units of ns/meter)
E_t -1.0e-6 ns/m August 9 - November 15 (0h UT)
VLA_X = -1601185.4;
VLA_Y = -5041977.5;
VLA_Z = 3554875.9;
Arm azimuths are N:355, E:115, W:236, close enough.
Phase in radians is then
Phase = 2 * pi * f * DELAY
So if the delay difference between calibrator and target is 0.01ns at
30 GHz, the phase difference is 1.8 radians or > 100 degrees.