; SNP2D ;--------------------------------------------------------------- ;! Task to convert SN table single-channel phase to delay ;# TASK CALIBRATION ;----------------------------------------------------------------------- ;; Copyright (C) 2013-2014 ;; 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 ;----------------------------------------------------------------------- SNP2D LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC SNP2D Convert single-channel phase to delay in SN table INNAME Input image name (name) INCLASS Input image name (class) INSEQ 0.0 9999.0 Input image name (seq. #) INDISK 0.0 9.0 Input image disk unit # INVERS Input table file version no. OUTNAME Output image name (name) OUTCLASS Output image name (class) OUTSEQ -1.0 9999.0 Output image name (seq. #) OUTDISK 0.0 9.0 Output image disk unit #. BIF 1.0 IF of channel used in CALIB in dataset INNAME BCHAN 1.0 Channel in BIF used in CALIB DOAPPLY -1.0 1.0 > 0 copy amplitudes in SN else force amplitude to 1.0. ---------------------------------------------------------------- SNP2D Task: In some cases, a strong spectral line is the best calibration source available. With the wide bandwidth of modern instruments, the phase measured at the frequency of the line cannot be transferred directly to calibrate all other channels. Instead, the measured phase needs to be interpreted as a delay and that delay applied to all IFs (spectral windows). Note that the antennas, source numbers, subarrays, frequency IDs, etc. in the output file must exactly match those in the input file. Otherwise, the information conveyed in the output SN file will be confusing at best. Note that the delay is simply the phase in turns divided by the frequency of the spectral channel used to determine the phase. This task determines the current frequency quite carefully using the same code as CVEL. You must set a rest frequency in the source table with SETJY if there is none to begin with. WARNING: This task is to be used AFTER you have done as good a job as possible with your absolute calibrator and your phase reference calibrator. Run a FRING on the former to take out gross delays and line up phases. Then run a FRING or CALIB as a function of time on the phase reference calibrator. Then run a CALIB on the reference spectral line preferably using a few rounds of self-cal (unless you know it to be a point source). SNP2D will then convert small phases into modest additional delays as a function of time. If there is any issue of phase wraps and the like, then this task will not do the right thing. If you used CALIB rather than FRING on the phase reference source, you may need to run CALIB again on that source after SNP2D (and CLCAL of course). Adverbs: INNAME.....Input image name (name). Standard defaults. INCLASS....Input image name (class). Standard defaults. INSEQ......Input image name (seq. #). 0 => 1. INDISK.....Disk drive # of input image. 0 => any. INVERS.....Version number of input SN table, 0 => highest OUTNAME....Output image name (name). ' ' => INNAME OUTCLASS...Output image name (class). ' ' => INCLASS OUTSEQ.....Output image name (seq. #). 0 => INSEQ OUTDISK....Disk drive # of output image. 0 => INDISK BIF........IF in data set INNAME containing channel used in CALIB - no default. BCHAN......Spectral channel of BIF in INNAME used in CALIB - no default. DOAPPLY....The real and imaginary parts of the gain determine the phase from which the output delay is computed. The output gain will have zero imaginary part (no phase). If DOAPPLY > 0, the output real part will be equal to the amplitude in the SN table of BIF. Otherwise, the output real part of the gain will be 1.0. ----------------------------------------------------------------