Description
Module measuresdata provides scripts to maintain and update
global data used by the Measures system. These include predicted and final
IERS earth orientation data, JPL planetary ephemerides, leap second data,
observatory positions, Earth magnetic field models, and others.
The global data are stored as AIPS++tables, and are required by the Measures
system for certain coordinate conversions, or to obtain the highest possible
precision.
Scripts to convert external ephemerides (e.g. for comets and
satellites) into a table are
also provided (createcomet and
createfromnorad.
A separate Glish script (measuresiers.g) is available to create and
update all the IERS tables in one go. It could e.g. be used in a regularly
running cron job (every 3 days) as:
glish -l measuresiers.g
When updating tables, the following should be observed:
- all data files, tables and scripts mentioned reside at
$AIPSROOT/code/trial/apps/measures and can be copied from there if necessary
- all Glish scripts should be run in the directory where the tables that
have to be upgraded or created are situated (copy them if necessary, and use
the aipsrc resource file to indicate to the system where they can be
found)
- for the upgrades to work the table files (i.e. the Table/table.*
files) should be writable (chmod +644 Table/table.* if necessary)
There are a number of main separate routines provided for the upgrade of the
different tables. They are:
- taiutc: checks if update of the
leap seconds table is required (it changes at most once per half
year). If a change has been possible, it
reads the tai-utc.dat file from the USNO, and converts it into
a table TAI_UTC in the current directory. The rows in the table are
MJD (start of the leap second change); dUTC (the leap second value as from
the MJD); Offset (necessary for earlier dates) and Multiplier (also for early
dates). The table in the system will in most cases be up-to-date.
(currently ftp:maia.usno.navy.mil/ser7/tai-utc.dat).
- ierseop97: checks if an update of
the final IERS Earth Orientation Parameters data is necessary (it changes
roughly once every week). If change is feasible, it
reads the C04 solution from the IERS, and creates/updates the IERSeop97 table in the current directory. It contains dUT, x, y (polar
motion), LOD (length-of-day),
dPsi and dEps (nutation) final values with their errors up till one to two
weeks ago. The table in the system starts at 1962 (as will be a table created
from scratch).
(currently ftp:hpiers.obspm.fr/iers/eop/eopc04/eop97c04.xx).
- ierseop2000: checks if an update of
the final IERS Earth Orientation Parameters data using the IAU2000
nutation/precession theory is necessary (it changes
roughly once every week). If change is feasible, it
reads the C04 solution from the IERS, and creates/updates the IERSeop2000 table in the current directory. It contains dUT, x, y (polar
motion), LOD (length-of-day),
dPsi and dEps (nutation) final values with their errors up till one to two
weeks ago. The table in the system starts at 1962 (as will be a table created
from scratch).
(currently ftp:hpiers.obspm.fr/iers/eop/eopc04/eop97c04_IAU2000.xx).
- ierspredict: checks if an update
of the IERS predictions is necessary (the predictions change about once every
three days). If appropriate it reads
the predicted data for dUT, x and y from the USNO file mark3,out and
updates the IERSpredict table. It contains dUT, x and y predicted
for the next 3 months. Also the file gpsrapid.out is read, providing
predictions for the next two weeks for dEps and dPsi (in future the last data
will be either calculated or taken from JPL data). The table in the system
starts at early 1997. A table created from scratch will start with the
earliest data available at the ftp site.
(currently ftp:maia.usno.navy.mil/ser7/mark3.out and
ftp:maia.usno.navy.mil/ser7/gpsrapid.out).
- ierspredict2000: checks
if an update of the IERS predictions using the IAU2000 theory is
necessary (the predictions change about once every
three days). If appropriate it reads
the predicted data for dUT, x and y from the USNO file mark3,out and
updates the IERSpredict2000 table. It contains dUT, x and y predicted
for the next 3 months. Also the file gpsrapid.out is read, providing
predictions for the next two weeks for dEps and dPsi (in future the last data
will be either calculated or taken from JPL data). The table in the system
starts at early 1997. A table created from scratch will start with the
earliest data available at the ftp site.
(currently ftp:maia.usno.navy.mil/ser7/mark3.out and
ftp:maia.usno.navy.mil/ser7/gpsrapid.out).
- jplde: checks if an update is
necessary. The tables do not change, but to limit space, the standard table
provided with the system is limited to the period from 1990 up to at least
two full years after the current date. In general the system table will obey these
rules, and an update will not be done. Tables for both DE200 (the IAU
standard) and DE405 (the most recent ones) are in the system. If data for
other periods is needed, the function can be run with start and end dates. The
AIPS++system contains data for the period 1960-2020. If data outside this
period is needed, the limits in the Glish script have to be changed. The data
will be loaded from JPL in that case (at 5-7Mb per 20 year span). The table
rows have an MJD and a large vector giving the Chebyshev polynomial
coefficients for the planets. Access of the table (as for the other tables)
can be made using functions provided in the MeasTable class, although,
of course, the table can be read directly.
(currently: ftp:navigator.jpl.nasa.gov/ephem/export/ascii/ascpxxxx.yyy)
- addobservatory: can add and
delete entries in the Observatories table. It backups the old table; sort
the entries on the observatory name, and capitalises the name and position
type. In principle the editing of the table can in future be done by the
tablebrowser, although no checks on the validity of the data will then be done.
(currently only updated by hand).
- addline: can add and
delete entries in the Lines table. It backups the old table; sort
the entries on the spectral name, and capitalises the name.
In principle the editing of the table can in future be done by the
tablebrowser, although no checks on the validity of the data will then be done.
(currently only updated by hand).
- addsource: can add and
delete entries in the Sources table manually, or using the USNO VLBI
reference source frame. It backs up the old table; sort
the entries on the source name, and capitalises the name and direction
type. In principle the editing of the table can in future be done by the
tablebrowser, although no checks on the validity of the data will then be done.
(currently ftp:maia.usno.navy.mil/rorf/refframe.one)
- createcomet: can create a table
of e.g. cometary data from an input file. The input file should be (at least
for now) in the "p120" format.
- createfromnorad: can create a
table
of e.g. satellite data from an input file. The input file should be (at
least
for now) in the "TRAKSTAR" ECI format.
- igrf: checks if update of the
International Geomagnetic Reference Field models table
is required (it changes every 5 years, with maybe a small update in
between).
If a change has been possible, it
reads the IGRF.COF file from the Goddard data center, and converts it into
a table IGRF in the current directory. The rows in the table are
MJD (start of every 5 year period); COEF, the Schmidt-normalised spherical
harmonic coefficients of the International
Geomagnetic Reference Field, produced
by the International Association of Geomagnetism and Aeronomy, Working
Group V-8: Analysis of the Global and Regional Geomagnetic Field and
its Secular Variation,
in the sequence:
g10, g11, h11, g20, g21, h21, g22, h22, g30, g31, h31, , g32, h32, g33,
h33, ..., h1010;
dCOEF, the annual change in the coefficients.
The table in the system will in most cases be up-to-date.
(currently ftp:ftp.ngdc.noaa.gov/SolidEarth/MainfldMag/Models/IAGA/IGRF.COF)
The tables are used in measures calculations. The TAI_UTC table is
essential for any direct or indirect (e.g. coordinate conversions) work with
the MEpoch classes. The DE200 and DE405 tables are essential
for positions within the solar system, and very accurate coordinate
conversions. The other IERS tables are necessary for high precision
coordinate conversion. For lower precision (at the single dish level) they
are not necessary. The IGRF tables are used for Earth' magnetic field
calculations.
All tables described here have the following keywords:
- VS_CREATE: the time of creation of the original table
- VS_DATE: the time of the last update of the table
- VS_VERSION: xxxx.yyyy, where yyyy is updated at every update; xxxx at
every new build
- VS_TYPE: a descriptive text of the table contents
- dMJD: the step between rows in the table in time (days), or zero if
irregular
- MJD0: the date of the first row in the table - dMJD
and have a Type=IERS.
The DE tables have a few dozen more constants, specifying data used in the
calculations. Access is provided through the MeasTable module.
The other methods provided are helper functions.
Example
> glish -l 'measuresiers.g'
will update the existing (or create if non-existent) tables with Earth
Orientation parameters TAI_UTC, IERSeop97, IERSpredict,
IERSeop2000, IERSpredict2000, and the Solar system
DE200 and DE404 tables.
The following example will only update (create) the prediction tables:
- include 'measuresdata.g'
- ierspredict()
- exit
Functions
Next: taiutc - Function
Up: General
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2006-08-01
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