; VLATECR ;--------------------------------------------------------------- ;! Calculate ionospheric delay and Faraday rotation corrections ;# PROCEDURE VLA ;----------------------------------------------------------------------- ;; Copyright (C) 2006, 2010, 2018, 2020 ;; 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 ;----------------------------------------------------------------------- VLATECR LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC VLATECR Procedure to calibrate ionospheric delay 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 # SUBARR Subarray to correct (0 => all) APARM Switches (1) if > 0 correct for dispersive delay (2) Follow ionosphere factor VLATECR is defined in the VLAPROCS run file. ---------------------------------------------------------------- VLATECR Type: Procedure Use: Automatically download IONEX files needed to correct the atmospheric Faraday rotation and optionally dispersive delay with TECOR. Then runs TECOR. See EXPLAIN TECOR for more information on these corrections. To perform the automatic download the system must have one of the following commands: wget, curl or ncftpget, and an NX table. VLATECR is defined in the VLAPROCS run file. 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. SUBARR.....Subarray to correct. 0 => all. APARM......Miscellaneous settings and switches. (1) Enable (> 0.5) or disable (<= 0.5) dispersive delay corrections. (2) In principle, it is thought that the ionosphere remains approximately fixed wrt the Sun. Thus, the task should predict which ionosphere is now in the direction of the source by applying a time correction to the apparent longitude while interpolating between the table values, which are only given every two hours. This sometimes seems in fact to do odd things. This parameter allows you to do only a fraction of the time correction, from epsilon to 1.0. 0 -> 1; < 0 -> 0. A correction of zero is equivalent to a model in which the ionosphere rotates with the earth. ---------------------------------------------------------------- VLATECR: Procedure that corrects the atmospheric Faraday rotation using TECOR. This procedure automatically downloads the IONEX files from the CDDIS archive. DOCUMENTOR: Amy Mioduszewski RELATED PROGRAMS: VLAPROCS, TECOR VLATECR is designed to make the use of TECOR easier. It uses the header and the NX table to calculate what files to download from CDDIS. It uses the CDDIS site in the US (cddis.gsfc.nasa.gov) and downloads the jplg or codg version of the IONEX files. Then it runs TECOR using these files. For simplicity (files from multiple days must to have the same prefix), all the files are renamed with the jplg prefix. The IONEX files are left in the /tmp area of your computer, so you can copy them for your records or ignore them. See EXPLAIN TECOR for more information. NOTE: The IONEX files can take up to a week to be available at CDDIS. This procedure is defined in VLAPROCS, type RUN VLAPROCS to load VLAPROCS. To run VLATECR: 1) The dataset must have a correct observation date in the header; if it is wrong correct it with PUTHEAD. -> there is a weak test on the validity of the observation date; the observation year must be <= to the creation year. 2) The dataset must have an NX table; run INDXR to create. 3) The system must have the command curl. VLATECR will test for the existence of this command. 4) /tmp directory must exist on your computer 5) Your computer must allow link to the Internet, some computers may have firewalls such that the above commands exist, but will not work. If there is a problem with the automatic download then you can download the IONEX file(s) manually and then run TECOR directly, setting INFILE and NFILES: Sometime in October 2020, for new requirements, you can consult https://cddis.nasa.gov/Data_and_Derived_Products/CDDIS_Archive_Access.html You may have to create an account with cddis in order to download in some other fashion. The command that does work from VLATECR is (all on one line!) curl -u anonymous:daip@nrao.edu --ftp-ssl ftp://gdc.ccdis.eosdis.nasa.gov/ gps/products/ionex/YYYY/DDD/jplgDDD0.YYi.Z > /tmp/jplgDDD0.YYi.Z (no blanks between gov/ and gps) where YYYY is the year e.g. 2015, YY is the last 2 digits of the year e.g. 15, and DDD is the day number within the year.