;--------------------------------------------------------------- ;! Calculate ionospheric delay and Faraday rotation corrections ;# Task Calibration VLA VLBI ;----------------------------------------------------------------------- ;; Copyright (C) 1998; 2001; 2003-2007, 2015 ;; 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 ;----------------------------------------------------------------------- TECOR LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC TECOR Task to calibrate ionospheric delay and Faraday rotn. 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 # INFILE IONEX file name NFILES 0.0 999.0 # of INFILES SUBARR Subarray to correct (0 => all) ANTENNAS Antennas to correct (all 0 => all) GAINVER Input CL table version GAINUSE Output CL table version APARM Switches (1) if > 0 correct for dispersive delay (2) Follow ionosphere factor ---------------------------------------------------------------- TECOR Task: Derives corrections for ionospheric Faraday rotation and dispersive delay from maps of total electron content in IONEX format. There are two procedures that will download the files automatically (including calculating the day number) and run TECOR. They are VLBATECR and VLATECR and they are part of the procedure packages VLBAUTIL and VLAPROCS respectively. See HELP VLBATECR or VLATECR for more info. 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. INFILE.....The name of the file containing the TEC data. The filename should be given in the usual AIPS style as a logical directory name followed by a colon and the name of the file or the directory path. The file should contain TEC maps spanning the time range covered by the input CL table and should be in IONEX format. If NFILES > 1 then the name MUST be in standard format CCCCdddC.yyC where C can be any character, ddd is the day number, and yy is the year. Also the name given in INFILE must be the first day. See EXPLAIN TECOR for more details. NFILES.....Number of IONEX files to use. Note that if NFILES > 1 then the INFILE must be in a standard format and the file in INFILE must be the first day of those to be loaded. 0 => 1 SUBARR.....Subarray to correct. 0 => all. ANTENNAS...A list of antennas to correct. If all entries are zero then all antennas in the subarray or subarrays selected by SUBARR will be corrected. If all of the entries are positive or zero then only those antennas with numbers corresponding to the positive entries will be corrected. If any entries are negative then all of the antennas in the selected subarray or subarrays will be corrected except those with numbers corresponding the the absolute values of the non-zero entries in this array. GAINVER....Version number of the input CL table to use. 0 => highest GAINUSE....Version number of output CL table. This must not be the number of an existing CL table. 0 => highest + 1 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. ---------------------------------------------------------------- TECOR: Task that corrects ionospheric Faraday rotation and dispersive delay using maps of ionospheric electron content. There are two procedures that will download the files automatically (including calulating the day number) and run TECOR. They are VLBATECR and VLATECR and they are part of the procedure packages VLBAUTIL and VLAPROCS respectively. See HELP VLBATECR or VLATECR for more info. DOCUMENTOR: Chris Flatters, Amy Mioduszewski, NRAO RELATED PROGRAMS: LDGPS, GPSDL, PCAL, LPCAL, VLBATECR, VLATECR most programs that apply calibration TECOR reads a set of maps of ionospheric electron content that covers the time range of the observations and uses this data to calculate the ionospheric Faraday rotation and, if you request it, the dispersive delay introduced by the ionosphere. The dispersive delay that is in put in the CL table (column DISP) is the dispersive delay at a wavelength of 1 meter. The input data is expected to be text files in IONEX format. The IONEX format is a standard format for the interchange of ionosphere maps and is used by NASA's crustal dynamics data interchange system (CDDIS), among others. Each IONEX file contains a series of maps of the zenith total electron content of the ionosphere as a function of geographical latitude and longitude taken at different times. TECOR expects the input file to contain maps covering the whole range of times contained in the AIPS data file. Some IONEX files may contain maps that do not cover all of the antenna in the array. If this is the case then you should use the ANTENNAS adverb to prevent TECOR from trying to determine corrections for antennas outside the covered area otherwise the calibration records for these antennas will be marked as invalid. Note that you only need to determine the ionospheric Faraday rotation for your phase reference antenna to calibrate polarization; differences between the antennas are removed by self-calibration. Dispersive delay corrections depend greatly on the accuracy of the input file and should therefore be checked carefully if they are turned on. Ionospheric models are available from the CDDIS data archive. There are 5 IONEX files produced by different groups for each day archived at CDDIS. These groups are the Jet Propulsion Laboratory (JPL), the Center for Orbit Determination in Europe (CODE), the Geodetic Survey Division of Natural resources Canada (EMR), the ESOC Ionosphere Monitoring Facility (ESA), and the Technical University of Catalonia (UPC). At this time, all the files provide maps every 2 hours. Since these things change so rapidly, it is difficult to recommend one file over another. For the best possible results try all the files and use the one that seems to work the best (this can be judged using VPLOT). If you only try one, there is a marginal recommendation that you use the JPL or CODE files. As mentioned above, there might come a time where one or more of these files will become significantly better than the others so downloading all the files might be a good idea even if you do not plan of trying them all (they are not large files). WHICH FILES TO DOWNLOAD ======================= The IONEX files being read in must bracket the entire experiment. BEFORE November 3, 2002 the IONEX files on the CDDIS archive spanned the time from 1:00 to 23:00. So if you have an experiment which starts before 1:00 or ends after 23:00 then you need to get IONEX files for the day of the experiment and the previous day or next day respectively. AFTER November 3, 2002 the IONEX files on the CDDIS archive span the time from 0:00 to 24:00. So you can now download files for only the days on which your experiment has data. ********************************************************************* * NOTE: There are two procedures that will download the files * * automatically (including calulating the day number) and * * run TECOR. They are VLBATECR and VLATECR and are * * part of the procedure packages VLBAUTIL and VLAPROCS * * respectively. See HELP VLBATECR or VLATECR for more info. * ********************************************************************* TO DOWNLOAD THE FILES: ====================== 1) ftp cddis.gsfc.nasa.gov; login as anonymous. -- note that there is a mirror site at igs.ensg.ign.fr 2) cd pub/gps/products/ionex/YYYY/DDD (YYYY-year; DDD-day number) -- for igs.ensg.ign.fr: cd pub/igs/iono/YYYY/DDD 3) prompt -1 4) mget jpl*.Z (or get jplgDDD0.YYi.Z) (not all *.Z !) 5) uncompress above file(s) before using TECOR If more than one file is needed to cover the time period of the experiment: -- download all the files -- make sure the files have the format CCCCdddC.yyC; where C is any character, ddd is the three digit day number and yy is the 2 digit year. This is designed to work with the standard file names that the CDDIS data archive uses. Note that the C's must be the same for each file and they must all be in the same directory. -- use the FIRST file as the INFILE -- set NFILES to the number of files Example: INFILE 'FITS:CODG1230.99I' NFILES 4 Will expect to find files: CODG1230.99I CODG1240.99I CODG1250.99I CODG1260.99I in directory $FITS.