; QUFIX ;--------------------------------------------------------------- ;! determines Right minus Left phase difference, corrects cal files ;# Task UV Calibration polarization SPECTRAL ;----------------------------------------------------------------------- ;; Copyright (C) 2011 ;; 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 ;----------------------------------------------------------------------- QUFIX LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC QUFIX: Task to apply Right - Left phase difference INNAME UV data (name) INCLASS UV data (class) INSEQ 0.0 9999.0 UV data (seq. #) 0 => high INDISK UV data Disk unit # 0 => any IN2NAME Good image (name) IN2CLASS Good image (class) IN2SEQ 0.0 9999.0 Good image (seq. #) 0=>high IN2DISK Good image disk unit 0=>any IN3NAME Uncal image data (name) IN3CLASS Uncal image (class) IN3SEQ 0.0 9999.0 Uncal image (seq. #) 0=>high IN3DISK Uncal image disk unit 0=>any PCUT 0.0 Use only Q,U values > PCUT in total polarization NBOXES 1.0 50.0 Number of boxes for averaging CLBOX -2.0 16384.0 Four coordinates for each box CALIN Text file with corrections OUTTEXT Text file w corrections not blank => do not apply ---------------------------------------------------------------- QUFIX Type: Task Use: Performs the function of RLDIF to correct the BP, CP, and PD tables in a spectral-line data set. These tables are produced by BPASS and PCAL but are on separate phase references in the two polarizations. This matters to cross-hand data. The best way to correct this problem is with RLDIF. But that requires a calibration source for which the Q and U spectrum or at least the polarization position angle as a function of frequency is well known. 3C286 is a good calibration source at all frequencies, but 3C48, for example, has significant, but poorly known polarization behavior at low frequencies and 3C147 has no polarized signal at these same frequencies. If you have images of a source which are well calibrated in Q and U and wish to correct data from another day that lacks the polarization position angle calibrator, QUFIX offers a solution. It compares two 4-dimensional images (Ra, Dec, freq, Stokes) to determine the rotation angle which will align the Q and U on average as a function of channel. This angle may be written out in a text file or simply applied to the tables of a UV data set. QUFIX offers the option of reading in a text file of corrections determined from a previous run of QUFIX or from any other method the user may devise. In that case, it does not require or use the two image 4-cubes. If your image is of a source with a spatially constant polarization angle (e.g. a point source), then QUOUT and RLDIF are better solutions for you. QUFIX is better used in the case of complex sources with spatially variable polarization position angle. Adverbs: **** Data set with tables to be corrected **** INNAME......UV file name (name). Standard defaults. INCLASS.....UV file name (class). Standard defaults. INSEQ.......UV file name (seq. #). 0 => highest. INDISK......Disk unit #. 0 => any. **** Well-calibrated Stokes-spectral cube **** IN2NAME.....Image file name (name). Standard defaults. IN2CLASS....Image file name (class). Standard defaults. IN2SEQ......Image file name (seq. #). 0 => highest. IN2DISK.....Disk unit #. 0 => any. **** Calibrated but not RLDIF Stokes-spectral cube **** IN3NAME.....Image file name (name). Standard defaults. IN3CLASS....Image file name (class). Standard defaults. IN3SEQ......Image file name (seq. #). 0 => highest. IN3DISK.....Disk unit #. 0 => any. **** control parameters **** PCUT........If determining the corrections from images, use only pixels having SQRT (Q*Q + U*U) > PCUT in both image cubes. NBOXES......Number (<=50) of rectangular or circular boxes to search in all Ra-Dec planes. CLBOX.......A 4x50 array with the parameters of each box. CLBOX(1,i)=-1 indicates a circle of radius CLBOX(2,i) pixels centered on (CLBOX(3,i), CLBOX(4,i)). CLBOX(1,i) >= 0 indicates a rectangular box. CALIN.......Text file containing the corrections as angles in degrees. - see below for format details. If CALIN is not blank, the 2nd and 3rd images will be ignored and the contents of CALIN used. OUTTEXT.....Text file output containing the corrections. If OUTTEXT is not blank, it will be used and no corrections will be applied to UV extension tables (first UV file ignored entirely). NOTES: 1. Images 2 and 3 must be aligned in all axes. 2. Images 2 and 3 (or CALIN) do not have to be aligned in frequencies with the UV data set. The corrections will be interpolated to the UV data set frequencies. 3. CALIN must be in strict increasing frequency order. CALIN file format: 1. Comment lines at any point begin in column 1 with either a ; or a # character. 2. Data lines contain the specified type of data columns: frequency in GHz, polarization angle in degrees Example: ;FAS # QUOUT run 12-JAN-2011 11:27:03 using CP version 2 # source is 3C286 with constant pol angle 33 # changed to corrections by 2 * (33 - pos ang) # # 4.988000000 32.97708 0 4.988000000 0.04592 # 4.990000000 32.97708 0 4.990000000 0.04592 # 4.992000000 33.01998 0 4.992000000 -0.03996 # 4.994000000 33.12441 0 4.994000000 -0.24882 # 4.996000000 33.31594 0 4.996000000 -0.63188 # 4.998000000 33.39096 0 4.998000000 -0.78192 ----------------------------------------------------------------