;---------------------------------------------------------------
;! Calculate ionospheric delay and Faraday rotation corrections
;# PROCEDURE VLA
;-----------------------------------------------------------------------
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;-----------------------------------------------------------------------
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)
           VLATECR is defined in the VLAPROCS run file.
----------------------------------------------------------------
VLATECR
Type: Procedure
Use:  Automatically download IONEX files needed to correct the
      atmospheric Faraday rotation with TECOR.  Then runs TECOR.
      See EXPLAIN TECOR for more information on this correction.
      To do 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.
----------------------------------------------------------------
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.
VLATECR uses APARM=0, (i.e., it does not do the dispersive delay
and does not adjust the direction of the Faraday rotation).

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 one of the following commands: wget, curl or
      ncftpget.  VLATECR will test for the existence of these commands
      in the order given above and will use the first one it finds.
      Mac OS - will probably have curl; wget and ncftpget seem to be
      available in Fink.
   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.
