; SWPOL ;--------------------------------------------------------------- ;! Swap polarizations in a UV data base ;# Task UV POLARIZATION ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 2000 ;; 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 ;----------------------------------------------------------------------- ;--------------------------------------------------------------- SWPOL LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC SWPOL Task which swaps polarizations in a UV data base 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 # OUTNAME Output UV file name (name) OUTCLASS Output UV file name (class) OUTSEQ -1.0 9999.0 Output UV file name (seq. #) OUTDISK 0.0 9.0 Output UV file disk unit #. ANTENNAS Antennas to swap SUBARRAY 0.0 99.0 Selected subarray DOCALIB Swap calibration info? ---------------------------------------------------------------- SWPOL Task: This task swaps polarization data streams in a UV data file. This allows data sets in which the polarization streams have been mislabelled to be corrected. Polarization streams may be mislabelled in VLA data if the transfer switch is set incorrectly or in VLBI data if the the normal/alternative IF switch is set to the wrong position at one or more telescopes. Calibration data in CL and SN tables may updated to reflect the altered polarization streams at the discretion of the user. SWPOL will handle both linear and circular polarizations but not a mixture of the two. SWPOL requires both both parallel hands (RR and LL or XX and YY) to be present and if any cross-hand (RL, LR, XY or YX) is present its conjugate cross-hand musty also be present. 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. OUTNAME....Output UV file name (name). Standard defaults. OUTCLASS...Output UV file name (class). Standard defaults. OUTSEQ.....Output UV file name (seq. #). 0 => highest unique OUTDISK....Disk drive # of output UV file. 0 => highest with space for the file. ANTENNAS...Antennas for which polarizations are to be swapped. If all entries are zero then polarizations are swapped for the whole array. If any entry is negative then all antennae *except* those listed are swapped. SUBARRAY...Subarray to process. 0 => subarray 1 DOCALIB....If > 0 then swap calibration information for selected antennas in CL and SN tables ---------------------------------------------------------------- SWPOL: Task to swap polarizations on one or more antennae Documentor: C. Flatters, NRAO-AOC (preliminary version) Related tasks: Most other UV tasks. SWPOL is intended to correct UV data sets in which the polarization data streams have been mislabelled at one or more telescopes. It handles either linear (X and Y are swapped for designated antennae) or circular polarization (R and L are swapped for designated antennae). In order to allow polarizations to be swapped for arbitrary subsets of telescopes there are a number of restrictions on the form of the input data. Principally, the polarization combinations in the data must correspond to one of the following sets: (RR, LL), (XX, YY), (RR, LL, RL, LR) or (XX, YY, XY, YX). Some examples of the use of SWPOL to correct common errors are given below. Example 1: The transfer switch is set incorrectly at the VLA. This leads to the labels for right and left circular polarization being applied to the wrong channel for the whole array. In this case set up the input and output file specifications and set the ANTENNAS array to all zeros. Example 2: One telescope in a VLBI experiment has set the normal/alt switch to the wrong position. This leads to RCP and LCP being recorded on the wrong tracks at that station; the diagnostic is wildly different amplitudes (commonly differing by a factor of 10) in the two parallel hands on baselines including that antenna. The solution is to find the number of the bad antenna using the 'MATX' output of LISTR, or using PRTAN if you already know the name of the telescope, and to set antennas using 'ANTENNAS = t, 0', where t is the antenna number of the bad telescope. DOCALIB should be set to true (> 0) to preserve phase-cals. DIAGNOSTIC MESSAGES The following messages indicate that the input data is not in a form that SWPOL can handle. SWINIT: COMPLEX AXIS MUST BE AXIS ONE This should not occur. If it does many other AIPS tasks will also fail on your data. SWINIT: MUST BE EITHER 2 OR 4 POLARIZATIONS PRESENT Self-explanatory. SWINIT: POLARIZATIONS INCOMPLETE OR MIXED The data contains a mixture of linear and circular polarizations or has a fragmentary set of polarizations (for example one parallel hand and one cross hand).