AIPS HELP file for VLATECR in 31DEC24
As of Thu Apr 25 10:20:13 2024
VLATECR: 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 #
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
factor
(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.
HELP SECTION
VLATECR
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
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.
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
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
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.
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 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
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 VLATECR 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.
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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 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
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