AIPS HELP file for TECOR in 31DEC24
As of Thu Oct 10 17:01:39 2024
TECOR: Task to calibrate ionospheric delay and Faraday rotn.
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 #
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
(3) > 0 use old model field
<= 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
DOTABLE > 0 -> write TE table to
examine TEC in detail
HELP SECTION
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.
Moving sources are supported if a PO table is present.
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.
Even for NFILES=1, the standard name is recommended
since the TE table will record the first 4 characters
after the : or / as the TECRTYPE.
See EXPLAIN TECOR for more details.
Compressed files are not allowed, but names ending in
.Z or .gz will have the .Z or .gz removed before being
read.
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. These are VERY important for
VLBA data and may even be useful for A-configuration
VLA data.
(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 (or 1 hour or even 30 minutes depending on
TECRTYPE). This works well most of the time, but
sometimes seems 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
> 0 use older simpler magnetic 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
DOTABLE....> 0 -> write a TE table. TEPLT then allows you to
examine in detail the TECs as functions of source, azimuth,
elevation etc etc
EXPLAIN SECTION
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 uses a model of the Earth's magnetic field to determine
the contribution of the ionosphere electrons to the observed
rotation measure. The default field is the official IGRF-13
model supported by Fortran code provided by the IGRF. See
the web page https://www.ngdc.noaa.gov/IAGA/vmod/igrf.html.
The reference is Alken, P., Thebault, E., Beggan, C.D. et al.
International Geomagnetic Reference Field: the thirteenth
generation. Earth Planets Space 73, 49 (2021).
https://doi.org/10.1186/s40623-020-01288-x
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 many 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). See the EXPLAIN for a current list of recognized
codes (not all of which may work).
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. *
*********************************************************************
Procedures VLATECR and VLBATECR determine which file(s) are needed and
attempt to download them automatically. If there is a problem with the
automatic download then you can download the IONEX file(s) manually and
set 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 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.
**************************************
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.
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.
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)
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