AIPS HELP file for VLBATECR in 31DEC25
As of Fri May 16 5:55:02 2025
VLBATECR: Procedure to calibrate ionospheric delay
INPUTS
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 #
SUBARRAY Subarray to correct
(0 => all)
TECRFILE IONEX file name
'' => download autmatically
TECRTYPE type of IONEX file to
download ' ' -> 'emrg'
NFILES # of TECRFILES
APARM Switches
APARM(1)=1 forced to do the
dispersive delay
(2) Follow ionosphere
factor
(3) <= 0 use IGRFv13 for
Earth magnetic field
> 0 old B field model
(4) TEC correction factor
default 1.
(5) TEC elevation increment
(km) default 0
(6) TEC elevation fudge
factor, default 1
VLBATECR is defined in the VLBAUTIL run file.
HELP SECTION
VLBATECR
Type: Procedure
Use: Automatically download IONEX files needed to correct the
ionospheric dispersive delay 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.
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.
SUBARRAY...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. ' ' -> 'emrg'
There are many possibilities - see the EXPLAIN.
NFILES.....Number of IONEX files to use. Note that if NFILES > 1
then the TECRFILE must be in a standard format and the
file in TECRFILE must be the first day of those to be
loaded. 0 => 1
APARM......Miscellaneous settings and switches.
(1) Enable (> 0.5) or disable (<= 0.5) dispersive
delay corrections. VLBATECR forces this to 1.
(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.
(3) <= 0 -> use IGRF version 13 magnetic field model for
the Earth
else use older model
(4)-(6) Leonid Petrov suggests a revised "mapping" function
See AJ, 2023, 165:183. Instead of
TEPATH = TEC / cos (ZAion)
use
TEPATH = TEC * APARM(4) / P
where
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.
Defaults:
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:
https://iopscience.iop.org/article/10.3847/1538-3881/acc174
EXPLAIN SECTION
VLBATECR: Procedure that corrects ionospheric dispersive delay
using TECOR. This procedure automatically downloads
the IONEX files from the CDDIS archive.
DOCUMENTOR: Amy Mioduszewski, NRAO
RELATED PROGRAMS: VLBAUTIL, TECOR
VLBATECR 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 emrg or user-specified 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 emrg (or other) 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 details on the ionospheric correction.
This procedure is defined in VLBAUTIL, type RUN VLBAUTIL to load
VLBAUTIL.
To run VLBATECR:
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 or VLBAFIX to create.
3) The system must have one of the following commands: wget, curl or
ncftpget. VLBATECR will test for the existence of these commands
in the order given above and will 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.
VLBATECR should be run on data of 8 GHz and lower, and can be run
anytime before the last fringe fit and after VLBAFIX. For simplicity,
it is recommended that it be run right after VLBAFIX or VLBAEOPS, so
all corrections to the data are done before calibration.
If there is a problem with the automatic download then you can download
the IONEX file(s) manually and set TECRFILE 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 VLBATECR is (all on one line!)
curl -u anonymous:daip@nrao.edu --ftp-ssl
ftp://gdc.cddis.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. The "jplg" is replaced with TECRTYPE in lower case.
**************************************
On or about Oct 1, 2023, new names for the JPL 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 anonymous:daip@nrao.edu --ftp-ssl
ftp://gdc.cddis.eosdis.nasa.gov/
gps/products/ionex/YYYY/DDD/JPL0OPSFIN_YYYYDDD0000_01D_02H_GIM.INX.gz
> /tmp/jplgDDD0.YYi.gz
and these files need gunzip rather the uncompress. The JPL is replaced
with TECRTYPE first 3 characters in upper case. The file name is
slightly different for CODG:
curl -u anonymous:daip@nrao.edu --ftp-ssl
ftp://gdc.cddis.eosdis.nasa.gov/
gps/products/ionex/YYYY/DDD/COD0OPSFIN_YYYYDDD0000_01D_01H_GIM.INX.gz
> /tmp/codgDDD0.YYi.gz
Other file codes changed to the new file name format at different dates.
These are known for esa, cod, egs, cas, emr, jpl, and upc codes only
and are implemented in the VLBATECR procedure.
**************************************
If you do not have curl or a firewall or other issue makes this command
fail then,
Try going to https://cddis.nasa.gov/archive/gnss/products/ionex/YYYY/DDD
You may need to create a login account to cddis to do this.
The commands below will not work after October 2020.
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
TECRTYPE possibilities include
Code Meaning
Date of name format change known
casg Final solution (Chinese Academy of Science)
esag Final solution (European Space Agency ESOC)
codg Final solution (Center for Orbit Determination in Europe)
igsg Final combined solution (IGS combined)
emrg Final solution (Space Weather Canada) now a better default
jplg Final solution (Jet Propulsion Laboratory)
upcg Final solution (Universitat Politecnica de Catalunya,
Barcelona)
esa files from 20221127 to 20230205 exist with wrong names
they can be downloaded using the web site cited above
The following appears useful even though it is a rapid rather
than final solution. Name format is still the old form.
uqrg Rapid high-rate solution, one map per 15 minutes, (UPC)
Rapid solutions, name still old format
uhrg Rapid high-rate solution, one map per hour, (UPC)
uprg Rapid solution (UPC)
Not recommended: They are rapid solutions and they
are not present in 2024
corg Rapid solution (CODE)
ehrg Rapid high-rate solution, one map per hour, (ESA)
esrg Rapid solution (ESA)
igrg Rapid solution (IGS combined)
Predictions are even less useful
c1pg 1-day predicted solution (CODE)
c2pg 2-day predicted solution (CODE)
e1pg 1-day predicted solution (ESA)
e2pg 2-day predicted solution (ESA)
ilpg 1-day predicted solution (IGS combined)
i2pg 2-day predicted solution (IGS combined)
u2pg 2 day predicted solution (UPC)
The previous list
c1pg (number '1'), c2pg, carg, casg, codg, corg, ehrg, emrg (good?),
esag, esrg, igrg, igsg, jplg, jprg, uhrg, upcg, uprg, uqrg, whrg, whug