; VLBACPOL ;--------------------------------------------------------------- ;# PROCEDURE VLBI UTILITY CALIBRATION POLARIZATION ;! Procedure to calibrate cross-polarization delays ;----------------------------------------------------------------------- ;; Copyright (C) 2001; 2006 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- VLBACPOL LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC VLBACPOL: Procedure to calibrate cross polarization delays INNAME UV file name (name) INCLASS UV file name (class) INSEQ 0.0 9999.0 UV file name (seq. #) INDISK 0.0 9.0 UV file disk drive # OUTDISK Disk for temporary files FLAGVER Flagging table GAINUSE Prior calibration CL NO DEFAULT SUBARRAY 0.0 99.0 Selected subarray BASELINE List of antennas; MUST CONTAIN REFANT REFANT Reference antenna; MUST BE HIGHEST OR LOWEST NUMBERED ANTENNA IN BASELINE LIST CALSOUR Calibrator source to use TIMERANG select time range with good SNR for RL and LR corr. SOLINT Solution interval (min) 0=> 10 minutes DPARM for strong sources, it is only necessary to set DPARM(4)=the int. time (sec). DPARM(1) and (8) are automatically set by procedure. for rest see HELP VLBACPOL OPCODE 'AVIF' => avg SB delays BADDISK Disk drive #'s to avoid ---------------------------------------------------------------- VLBACPOL Procedure: This procedure uses a selected subset of a uv data set to determine cross polarized multi- and single-band delays. The average single-band and multi-band delays will be written into an SN and CL table. See EXPLAIN VLBACPOL for details. Before attempting to use VLBACPOL the RUN file VLBAUTIL must be run to define the procedure. This is done by: >RUN VLBAUTIL and only needs be done once. VLBACPOL creates several temporary files which it will destroy if able. The names of these files are fixed and must be destroyed if a previous attempt at VLBACPOL failed. Also the output files must not exist before running VLBACPOL. To execute the procedure simply type: >VLBACPOL 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. OUTDISK....Disk for temporary files 0=>INDISK. FLAGVER....Flag table version to apply GAINUSE....CL table from prior calibration to apply before determining solutions. There is no default. SUBARRAY...Subarray to use. BASELINE...List of antennas, normally the reference antenna and the others to be used, see EXPLAIN VLBACPOL. NOTE: the reference antenna should have a number either above or below ALL other antenna numbers. REFANT.....Reference antenna. MUST BE HIGHEST OR LOWEST NUMBERED ANTENNA LISTED IN BASELINE CALSOUR....Calibrator source(s) to use. TIMERANG...Time range of the data subset. SOLINT.....The FRING solution interval (min), 0=> 10 minutes DPARM......Delay rate parameters. DPARM(1)...Number of baseline combinations to use in the initial, coarse 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. THIS PARAMETER IS AUTOMATICALLY SET TO 1 IN THIS PROCEDURE!!! DPARM(2)...The delay window to search (nsec) centered on 0 delay. 0 => full Nyquist range defined by the frequency spacing. If DPARM(2) < 0.0 no delay search will be performed. DPARM(3)...The rate window to search (mHz) centered on 0 rate. 0 => full Nyquist range defined by the integration time. DPARM(4)...The minimum integration time of the data (sec); 0 => search the data to find the minimum integration time. The correct minimum of all baselines should be supplied. DPARM(5)...If > 0 then don't do the least squares solution. If the least squares solution is not done then only the coarse search is done and much less accurate solutions are obtained. DPARM(6)...If > 0 then the output data will not be averaged in frequency else, all frequencies in each IF will be averaged. Affects single source files only. DPARM(7)...If > 0 then the phase, rate and delays will not be re-referenced to a common antenna. This option is only desirable for VLBI polarization data. DPARM(8)...DPARM(8)>0 allows zero'ing of RATE, DELAY, and/or PHASE solutions. ** Note that the ZEROing is done _AFTER_ the FRING solution is found, this is not the mechanism for turning off the DELAY, RATE, or PHASE search, see DPARM(2-3) for that capability. ** DPARM(8) value zero RATES? zero DELAYs? zero PHASEs? 0 No No No 1 Yes No No 2 No Yes No 3 Yes Yes No 4 No No Yes 5 Yes No Yes 6 No Yes Yes 7 Yes Yes Yes THIS PARAMENTER IS AUTOMATICALLY SET TO 1 IN THIS PROCEDURE!!! OPCODE.....'AVIF' means average single band delays corrections in IF, else do each IF independently. The best value depends on the SNR. BADDISK...Disk drive #'s to avoid for scratch files ---------------------------------------------------------------- VLBACPOL: Make an SN for the calibration of cross polarized delays. Documentor: W. D. Cotton Related Programs: SWPOL, FRING, POLSN, CLCAL Calibration of cross polarized delays This procedure will take a selected subset of a uv data set and determine the corrections needed to remove differences in single and multiband delays for the right and left handed systems. The output is an SN and CL. The output SN and CL tables will be written to the input data set and on successful completion of VLBACPOL will be the highest version SN/CL table. Cross polarized rate errors are assumed to be zero. This should run after correcting the instrumental delays (VLBAPCOR) and before or after fringe fitting. The basic steps of this procedure are the following: 1) Run UVCOP to select a short section of data for one or more antennas and the reference antenna. This time/source/baseline combination should have a reasonable SNR for the RL and LR correlations. 2) Run FRING on this segment of data to obtain corrections for the parallel fringes. Use APARM=2,0; DOCAL=1; SNVER=1. Other FRING parameters are as passed to the procedure either explicitly in the inputs file or implicitly by the appropriate adverb values. 3) Use CLCAL to apply this SN table to the CL table used to calibrate the input to FRING. 4) Use SWPOL to swap the polarizations of the reference antenna. Set ANTENNAS = ref. antenna; DOCALIB = 1 5) Run FRING as before but on the output of SWPOL. Do this once for each antenna in the BASELINE array with the reference antenna. 6) Run POLSN on the SN table produced by FRING. 7) Use TACOP to copy the SN table produced by POLSN to the original data set. 8) Run CLCAL to apply this SN table to the CL table given in GAINUSE. There are 2 lines at the end which will state which SN and CL tables contain the corrections. This procedure will create a number of temporary files on OUTDISK. These temporary files will have name 'CROSSPOL TMP' and should be deleted by the procedure on successful completion. As the names are fixed any residual files from a previous run of CROSSPOL should be deleted before executing the procedure.