As of Wed Apr 17 9:48:03 2024

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)
TECRFILE                           IONEX file name
                                   '' => download autmatically
TECRTYPE                           type of IONEX file to
                                   download  ' ' -> 'jplg'
APARM                              Switches
                                     (1) if > 0 correct for
                                         dispersive delay
                                     (2) Follow ionosphere
                                     (3) > 0 use IGRFv13 for
                                         Earth magnetic field
                                     (4) TEC correction factor
                                         default 1.
                                     (5) TEC elevation increment
                                         (km) default 0
                                     (6) TEC elevation fudge
                                         factor, default 1
           VLATECR is defined in the VLAPROCS run file.


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
      VLATECR is defined in the VLAPROCS run file.
  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.
  TECRFILE...Input file.  If ''=> file will be automatically downloaded.
             If there is a problem with automatic downloads (this can
             be a problem with some firewalls) the file can be can
             be downloaded manually.  See EXPLAIN VLBATECR for details
             on how to download the file(s).
             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.
  TECRTYPE...Type of IONEX file to download.  ' ' -> 'jplg'
             There are many possibilities: c1pg (number '1')
             c2pg, carg, casg, codg, corg, ehrg, emrg (good?),
             esag, esrg, igrg, igsg, jplg, jprg, uhrg, upcg,
             uprg, uqrg, whrg, whug
  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
             (3) > 0 -> use IGRF version 13 magnetic field model for the
                 else   use older model
             (4)-(6) Leonid Petrov suggests a revised "mapping" function
                 See AJ, 2023, 165:183.  Instead of
                     TEPATH = TEC / cos (ZAion)
                     TEPATH = TEC * APARM(4) / P
                     P = sqrt (1 - Rf^2 * cos^2 (a*EL))
                     Rf = (Rearth / (Rearth + Alt + APARM(5))
                     a = APARM(6)
                 Petrov recommends 0.85, 56.7 km, 0.9782.
                    If APARM(4) < 0.1 or > 5, APARM(4) = 1
                    If APARM(5) < -200 or > 200, APARM(5) = 0
                    If APARM(6) < 0.5 or > 2, APARM(6) = 1
                 web reference:


VLATECR: Procedure that corrects the atmospheric Faraday rotation
         using TECOR.  This procedure automatically downloads the
         IONEX files from the CDDIS archive.
DOCUMENTOR: Amy Mioduszewski

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 (
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

This procedure is defined in VLAPROCS, type RUN VLAPROCS to load

   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

Sometime in October 2020, for new requirements, you can consult

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 --ftp-ssl
   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.


On or about Oct 1, 2023, new names for the TEC files were introduced for
files created after day 219 (Aug 7).  Files from before use the above
naming convention.  The new names are

curl -u --ftp-ssl
 > /tmp/jplgDDD0.YYi.gz

and these files need gunzip rather the uncompress