; DIGICOR ;--------------------------------------------------------------- ;! specifies whether VLBA digital corrections are to be applied ;# ADVERB CALIBRATION ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 2013 ;; 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 ;----------------------------------------------------------------------- ;--------------------------------------------------------------- DIGICOR LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC ---------------------------------------------------------------- DIGICOR Type: Adverb (Logical, > 0 => true) Use: Standard data selection adverb. True (1) means apply the digital corrections to VLBA data in FITLD. False (-1,0) means do not apply the corrections. Null value: false (-1) Tasks: FITLD....Reads FITS files to load images or UV (IDI or UVFITS) data to disk. DIGICOR use for IDI only: Data processed in digital correlators such as the VLBA correlator and DiFX are affected by a variety of phenomena that we collectively refer to as digital effects. FITLD is able to apply the corrections needed to scale the data to the values that would be returned by a purely analogue correlator. DIGICOR = -1 will turn off the application of these correction, DIGICOR = 0 or 1 will apply them to both cross and total power, DIGICOR = 2 will apply the corrections to cross-power and only to total power if zero-padding was used in the correlator. The latter case is designed to deal with a situation in which the total-power spectrum is dominated by multiple, strong spectral lines. In that case, if zero-padding was not used, the reconstructed total-power spectrum, after an FFT, is inaccurate at some level. In all continuum cases DIGICOR = 1 should be the default. In nearly all line cases DIGICOR = 1 is fine. only if the Tant in the line is about equal to the Tsys should DIGICOR = 2 be used. One word of caution, for data correlated prior to Aug 1 1994 the correlator was incorrectly scaling the data by a factor of 1.57 (i.e. PI/2) . So for that data, DIGICOR can be used but a BFACTOR of 0.6369 (i.e. 1/1.57) should be applied in APCAL or to the final images. Unfortunately FITLD had no knowledge of the date of correlation so cannot perform this correction. The code detects data from the DiFX correlator and applies a different (1.0) saturation correction in that case. **** FITLD no longer alters DIGICOR for non-VLBA arrays, **** so set it carefully. Before 5 Feb 2013, it changed **** DIGICICOR to -1 if the array name was not VLBA. **** Note that DiFX correlators may write VLBA as the **** array even when no VLBA antennas are involved. ----------------------------------------------------------------