
INTERNATIONAL EARTH ROTATION
SERVICE (IERS) SERVICE
INTERNATIONAL DE LA
ROTATION TERRESTRE 
SERVICE DE LA ROTATION TERRESTRE RAPID
SERVICE/PREDICTION CENTRE
OBSERVATOIRE DE PARIS U.S.
NAVAL OBSERVATORY
61
Av. de l'Observatoire 3450
Massachusetts Avenue, NW
75014 PARIS (France) WASHINGTON,
DC 203925420 (USA)
Tél. : 33 (0) 1 40 51 22 26 1
202 762 0060
FAX :
33 (0) 1 40 51 22 91 1
202 762 1563
Internet : iers@obspm.fr ser7@maia.usno.navy.mil
August 2004
EXPLANATORY
SUPPLEMENT
TO IERS
BULLETINS A AND B
IERS
Bulletins A and B provide current information on the Earth's orientation in the
IERS Reference System. This includes
Universal Time, coordinates of the terrestrial pole, and celestial
pole offsets. Bulletin A gives an
advanced solution updated weekly by email subscription or daily by anonymous
ftp; the standard solution is given monthly in Bulletin B. The Annual Report
contains information on the data used, the models, the algorithms, and the reference
frames, as well as revised solutions for the past years. All solutions are
continuous within their respective uncertainties. Bulletin A is issued by the IERS Rapid
Service/Prediction Centre at the U.S. Naval Observatory, Washington, DC and
Bulletin B is issued by the IERS Earth Orientation Centre at the Paris
Observatory.
Bulletin A is intended for users who need accurate information before
the Bulletin B “finals” series is available, i.e., those who reduce data in the
very recent past (require rapid service) or those who operate in realtime
(require predictions). Bulletin B is
intended for standard use. For
scientific and longterm analyses of the Earth's orientation, users are advised
to request the longterm continuous series maintained by the Earth Orientation
Centre from 1846 (pole components), 1962 (UT), and 1981 (dPsi, dEpsilon) to the
current date. All solutions are
available electronically (see Section VIII).
Resolutions adopted at the 24th General
Assembly of the International Astronomical Union (IAU) recommend the
implementation of new procedures concerning the transformation between the
celestial and terrestrial reference systems: adoption of a new
precession/nutation model (IAU 2000), a new celestial pole (the Celestial
Intermediate Pole), and a new transformation between the terrestrial and celestial
systems defining UT1 as directly proportional to the Earth rotation angle. These
resolutions were implemented in Bulletins A and B on January 1, 2003 and are
discussed below.
I.
THE IERS CONVENTIONS
The IERS uses the following conventions:
A. The International Celestial and Terrestrial Reference
Systems
The International Celestial and Terrestrial Reference Systems
(respectively ICRS, ITRS) are defined by their origins, directions of axes and,
in the case of the ITRS, length unit.
The ICRS is described by Arias et al. (1995). Its origin is at the barycenter of the solar
system. The directions of its axes are
fixed with respect to the quasars to better than +/ 20 microarcseconds; they
are aligned with those of the FK5 within the consistency of the latter (+/ 80
milliarcseconds at epoch J1991.25 (van Leeuwen et al., 1997). The ICRS is realized by estimates of the
coordinates of a set of extragalactic sources:
the International Celestial Reference Frame (ICRF) (Ma and Feissel,
1997; Ma et al., 1998). According to Resolution
B2 of the International Astronomical Union (IAU) 23rd General Assembly (Kyoto, 1998), after 1
January 1998 the IAU celestial reference system is the International Celestial
Reference System (ICRS) as defined by the International Earth Rotation Service
(IERS) and the corresponding fundamental reference frame is the ICRF constructed
by the IAU Working Group on Reference Frames.
The IERS was asked to monitor the maintenance of the ICRS and its ties
to the reference frames at other wavelengths.
In the present IERS structure, two groups share this task: the
International VLBI Service for Geodesy and Astrometry (IVS) and the IERS ICRS
Centre, which is jointly operated by the Paris Observatory and the U.S. Naval
Observatory.
The ITRS origin is at the center of mass of the entire Earth system,
including the oceans and the atmosphere.
Its length unit is the meter (SI), consistent with the TCG time
coordinate for a geocentric local frame.
The orientation of its axes is consistent with that of the BIH System at
1984.0 within +/ 3 milliarcseconds.
The International Reference Meridian (IRM) is implicitly defined through
the adoption of the set of coordinates of stations realizing the ITRF.
Its time evolution in orientation is such that it has no residual
rotation relative to the Earth's crust.
The ITRS is realized by estimates of the coordinates and velocities of a
set of observing stations, the International Terrestrial Reference Frame
(ITRF). For more details, see Boucher et
al. (1996) and the IERS Conventions (2003) (McCarthy and Petit, 2004). A new
ITRF realization (ITRF2000) is now available (http://lareg.ensg.ign.fr/ITRF/).
B. IERS constants and models
The IERS Conventions (2003) (McCarthy and Petit, 2004) are a set of
constants and models used by the IERS Technique and Analysis Centres for Very
Long Baseline Interferometry (VLBI), Global Positioning System (GPS), satellite
radio positioning (DORIS), Satellite Laser Ranging (SLR), and by the IERS
Product Centres in the combination of results.
The values of the constants are adopted from recent analyses. In some cases, they differ from the current
IAU and International Association of Geodesy conventional ones. The models are, in general, the best
estimates of the specialists in the field.
Observations have shown that
there are deficiencies in the IAU 1976 Theory of Precession and the IAU 1980
Theory of Nutation. As a result the IAU
has adopted the IAU 2000 precessionnutation model (see IERS Conventions (2003)
[McCarthy and Petit, 2004]). This model
was implemented by the IERS as of 1 January 2003.
II. TIMESCALES USED IN BULLETINS a AND b
TAI is the atomic time scale calculated by the BIPM. Its unit interval is exactly one SI second at
mean sea level. The origin of TAI is such
that UT1TAI was approximately 0 on 1 January 1958. The instability of TAI is about six orders of
magnitude smaller than that of UT1.
UTC is defined by the International Radio Consultative Committee (CCIR)
Recommendation 4604 (CCIR, 1986). It
differs from TAI by an integral number of seconds in such a way that UT1UTC
remains smaller than 0.9s in absolute value.
The decision to introduce a leap second in UTC to meet this condition is
the responsibility of the IERS; it is announced in Bulletin C. According to the CCIR Recommendation, first
preference is given to opportunities at the end of June and December and second
preference to those at the end of March and September. Since the system was introduced in 1972, only
dates in June and December have been used.
A new definition of UTC is under discussion by the IAU and the
International Telecommunication Union, but no action is anticipated before
2006.
III. THE EARTH ORIENTATION PARAMETERS, DEFINITION BEFORE
JANUARY 1, 2003
The IERS Earth Orientation Parameters (EOP) describe the rotation of the
ITRS relative to the ICRS, in conjunction with the conventional
PrecessionNutation model.
A. The coordinates of the Celestial
Ephemeris Pole (CEP) relative to the International Reference Pole (IRP) are
defined as x and y. The CEP differs from
the instantaneous rotation axis by quasidiurnal terms with amplitudes under
0.01" (see Seidelmann, 1982). The
xaxis is in the direction of the IERS Reference Meridian (IRM), the yaxis is
in the direction 90 degrees West longitude.
B.
UT1 is the rotation angle about the pole. It is defined by a conventional relationship between
the origins of the terrestrial and celestial reference frames (Capitaine et
al., 2000, Capitaine et al., 2003, McCarthy and Petit, 2004). This relationship was developed to maintain
consistency with the previous defining relationship (Aoki et al., 1982). It gives access to the direction of the
International Reference Meridian (IRM) in the ICRS, reckoned around the CEP
axis. It is expressed as the difference
UT1TAI or UT1UTC.
DUT1 is the difference UT1UTC expressed with a precision of +/ 0.1s;
it is broadcast with the time signals and announced in Bulletin D. The changes in DUT1 are decided by the IERS.
The difference between the astronomically determined duration of the day
(D) and 86400s of TAI, is called length of day (LOD). Its relationship with the angular velocity of
the Earth, Omega, is:
Omega = 72 921 151.467064 
0.843994803 D, where Omega is in picoradians/s and D in ms.
UT1, hence D and Omega, are subject to variations due to zonal
tides. The model, which is a part of the
IERS Conventions, includes 62 periodic components with periods ranging from 5.6
days to 18.6 years. UT1R, DR, and OmegaR are the values of UT1, D, and Omega
corrected for the shortterm part of the model by Yoder et al. (1981), i.e.,
the 41 components with periods under 35 days.
In absolute value UT1RUT1 is smaller than 2.5 ms, LODRLOD is smaller
than 1 ms. As recommended in IERS
Gazette #13 (McCarthy and Gambis, 1997), IERS Earth orientation data are
produced at daily intervals and do not include the effects of semidiurnal and
diurnal variations; Ray's model has been adopted for interpolation. The corresponding numerical program is
available from either Centre’s ftp site, see McCarthy and Gambis (1997) for
details.
C.
The IERS continues to provide the offset in longitude dDy_{1980} and in obliquity dDe_{1980} with respect to the IAU
1976 Theory of Precession and the IAU 1980 Theory of Nutation. Following the
implementation of the IAU 2000 precessionnutation model in 2003, however, the
IERS also provides offsets with respect to this model. The offsets dDy_{1980} and dDe_{1980} are labeled dpsi and
deps in the released
IERS EOP Bulletin A, and Bulletin B.
IV. THE EARTH ORIENTATION PARAMETERS, DEFINITION AFTER
JANUARY 1, 2003
A. New
parameterization of the Earth orientation
The most important changes are those
introduced by IAU Resolutions B1.6 (IAU 2000 PrecessionNutation Model), B1.7
(Definition of Celestial Intermediate Pole), and B1.8 (Definition and Use of
Celestial and Terrestrial Ephemeris Origins).
The new precessionnutation model is accompanied by a new formulation
for the transformation between the celestial (CRS) and terrestrial (TRS)
reference systems in the form recommended in the IERS Conventions (2003) (McCarthy
and Petit, 2004):
_{},
in which _{}, and _{} are timedependent
transformation matrices to account for the precessionnutation, proper rotation
of the Earth about the axis corresponding to CIP, and polar motion,
respectively:
_{}, and
_{}.
The Earth rotation angle between the CEO and TEO is given as
function of UT1 by a simple linear relation:
q(T_{u})
= 2p(0.779 057 273
264 0 + 1.002 737 811 911 354 48
T_{u})
where .
Here _{} and _{} describe the position
of the Celestial Intermediate Pole (CIP) and the Celestial/Terrestrial
Ephemeris Origins (CEO, TEO) in the Geocentric Celestial Reference System
(GCRS) and International Terrestrial Reference System (ITRS), respectively (see
http://maia.usno.navy.mil/ch5tables.html). The developments of X, Y, and s into
Poisson series, based on the IAU 2000A precession/nutation model, are published
by Capitaine et al. (2003) and are available in the IERS Conventions (2003).
Expressions for the classical transformation based on the new IAU 2000 model
have been developed to be equivalent in the new transformation (IERS
Conventions (2003)).
1) Celestial pole offsets
Precessionnutation is referred to the CIP that exhibits, by
definition, only longperiodic motions with periods of two days and longer in
space. The IERS provides the celestial
pole offsets dX_{2000} and dY_{2000} referred to
the new model IAU 2000 following the new formalism and the quantity s. Classical nutation angles, the celestial pole
offsets in longitude and obliquity (dDy_{2000 }, dDe_{2000}),
respectively, referred to the new model can be easily derived from (dX_{2000 }, dY_{2000}) using
equations 23 in Chapter 5 of the IERS Conventions (2003) or the relative
Fortran subroutine dXdY_dpsideps included in the package, uai2000.package (see
next paragraph for its availability).
These values dX and dY are now smaller than 1 mas, reflecting mostly the effect of the
Free Core Nutation (FCN) that is not predictable and therefore not incorporated
into the new model. The position of the
CEO, given by s, is insensitive to any small change of the
precessionnutation at the level of one mas, so only its model values are to be
used (http://maia.usno.navy.mil/ch5tables.html). In parallel with these values, the values of
the ‘classical’ celestial pole offsets dDy_{1980} and dDe_{1980} referred to the old IAU 1976 Precession and 1980 Nutation model are
also being published in Bulletin A and Bulletin B.
2) Polar motion
Polar motion
is not affected by adopting the IAU 2000 resolutions. Polar motion contains (relatively small)
diurnal and subdiurnal terms, due to ocean tides and highfrequency nutation
terms. These are not part of the
polar motion values published by the IERS at daily intervals; they are
represented by a model (IERS Conventions (2003), Chapters 5 and 8) and should
be added after interpolation. The Earth
Orientation Centre makes available a Fortran subroutine for such an
interpolation (ftp://hpiers.obspm.fr/eoppc/models/interp.f). The position of the TEO, given by s’,
depends on the actual polar motion but the value of s’ is so small that
a simple linear approximation (Lambert and Bizouard, 2002) is sufficient:
s' =  47 mas (t  51544.5) / 36525
where t is expressed in modified Julian days
(MJD).
3) Universal
Time
UT1UTC is theoretically not affected by
the resolutions. Although UT1 is now
directly linked to the Earth rotation angle through the linear relation above,
the positioning of CEO (represented by the quantity s) and IAU2000
expressions between sidereal time and universal time UT1 are such that
continuity in UT1 is ensured at the epoch of change from the old system.
There are shortperiodic (diurnal,
semidiurnal) variations in UT1 due to ocean tides that are treated similarly
to polar motion (the IERS publishes the daily values from which these terms
have been removed, and they are to be added back after the interpolation).
B. Availability of new products and models
Since
January 2003, the IERS Rapid Service/Prediction Centre and IERS Earth
Orientation Centre have been publishing Bulletin A and Bulletin B containing dX and dY with respect
to IAU 2000A
precession/nutation model in parallel to the current issue containing (dDy, dDe)_{1980}.
The new Bulletin A files are available at the
following ftp sites:
 anonymous ftp: maia.usno.navy.mil
files : /ser7/finals2000A.daily
/ser7/finals2000A.data
The new Bulletin B files are available at the
following Web/ftp sites:
 Web:
http://hpiers.obspm.fr/eoppc/bul/bulb/
 anonymous ftp: hpiers.obspm.fr
files : / eoppc/bul/bulb/
C. Fortran subroutines
1) Transformation of (dX, dY)_{2000} to (dDy, dDe)_{1980} or (dDy, dDe)_{2000} and inversely are
available in Fortran 77/90 at :
 Web page:
http://hpiers.obspm.fr/eoppc/models/models.html#software
Files:

ftp://hpiers.obspm.fr/eoppc/models/uai2000.package

ftp://hpiers.obspm.fr/eoppc/models/uai2000.package.readme
 anonymous ftp:
hpiers.obspm.fr
files :
/eoppc/models/uai2000.package
/eoppc/models/uai2000.package.readme
2) Interpolation of Polar Motion at hourly scale
 Web:
http://hpiers.obspm.fr/eoppc/models/models.html#software
Files:
 ftp://hpiers.obspm.fr/eoppc/models/interp.f

ftp://hpiers.obspm.fr/eoppc/models/interp.readme
V.
THE DATA ANALYSIS
The data analysis that yields the
values of the EOP published in Bulletins A and B includes several steps that
are summarized below.
1. The individual Technique Centres
coordinated the observations made using the VLBI, SLR, GPS, and DORIS networks.
2. Analyses (operational and
refined) are done by the Analysis Centres of the Technique Centres. The operational results are transmitted in
parallel to the IERS Rapid Service/Prediction Centre to contribute to Bulletin
A and to the IERS Earth Orientation Centre to contribute to Bulletin B. The operational results are also archived at
each centre. The refined results are
computed yearly.
3. The IERS Rapid Service/Prediction
Centre performs additional processing of operational results. The IGS GPS satellite orbit data are used to
estimate a GPS UT1like quantity, and atmospheric angular momentum (AAM)
analysis and forecast data from NOAA and the IERS Global Geophysical Fluid Center’s
Special Bureau of the Atmosphere are used to estimate an AAM UT1like quantity.
4. General adjustment of ICRF, ITRF,
and EOP by the IERS Product Centres are based on the refined annual
results. This adjustment, described in
the IERS Annual Report provides the basis for determining the systematic
corrections to be added to the individual series in order to bring them into
the IERS Reference System. These
corrections are used in step 6. The
general results are published in the IERS Annual Report and longterm
monitoring results were given by Gambis (2000).
5.
Determination of EOP by the IERS Rapid Service/Prediction Centre is in
the form of slightly smoothed solutions at oneday intervals. This involves the application of systematic
corrections and statistical weighting.
The accuracy of this solution is given in Table 1. The results are published in Bulletin A with
a delay of about 18hours between the date of publication and the last
available date with estimated EOP. The
details of the procedure are outlined in McCarthy and Luzum (1991a).
6.
Determination of EOP by the IERS Earth Orientation Centre is in the form
of combined solutions derived from the individual series. Various solutions are computed: normal values
at fiveday intervals and slightly smoothed solutions at oneday and fiveday
intervals. In the procedure systematic
corrections determined in step 4 and statistical weighting is applied. The accuracy of these solutions is given in
Table 1. The results are published in Bulletin
B with a delay of thirty days between the date of publication and the last date
of the standard solution.
7.
Bulletins A provides predictions of the EOP while Bulletin B gives an
extrapolation of the standard solution. Details of the procedure used for
Bulletin A are given in McCarthy and Luzum (1991b) . Their performances are given in Table 1.
Table 1: Precision of the current solutions. The accuracy which includes the uncertainty of the tie to the IERS
System can be estimated by adding quadratically 0.0002" in terrestrial
pole, 0.00003s in UT1, and 0.0002" in celestial pole.
Solutions 

Terrestrial
Pole 
UT1 
Celestial Pole 


0.001" 
0.0001s 
0.001" 
Bulletin
A daily Prediction 
1d 5d 10d 20d 40d 90d 
0.1 0.6 2.6 4.8 9.0 16.1 25.6 
0.2 1.1 4.2 8.8 20.3 49.9 125.0 
0.3 0.3 0.3 0.3 0.3 





Bulletin
B daily 

0.1 
0.2 
0.3 



































VI.
CONTENTS OF BULLETINS A AND B
A. BULLETIN A (weekly and daily)
General information including key
definitions and the most recently adopted values of DUT1 and TAIUTC.
Quicklook daily (finals.daily) and
weekly (finals.all and finals.data) estimates of the EOP are determined by
combining the most recently available observed and modeled data (including VLBI
24hour and intensive, GPS, and AAM).
The combination process involves applying systematic corrections and
slightly smoothing in order to remove the high frequency noise. The SLR data type is updated for the weekly
estimates.
The daily solutions contain
predictions of x, y, and UT1UTC daily up to 90 days following the last day of
data in Section 4, while the weekly solutions contain predictions of x, y,
UT1UTC daily up to 360 days following the last day of data and smoothed daily
values of celestial pole offsets. The
results are published with a delay of about 18hours between the date of
publication and the last available date with estimated EOP.
To bring the Bulletin A (weekly and
daily) EOP solutions in compliance with IAU 2000 resolutions, additional files
(finals2000A.daily and finals2000A.data) are available which contain dX and dY with
respect to IAU 2000A
precession/nutation theory.
B.
BULLETIN B (Monthly)
Section 1: Five days sampling of section 2. Final Bulletin B values over one month and
provisional extension over the next three months.
Section 2: Smoothed values of x, y,
UT1UTC, UT1UT1R, dDy, and dDe
at oneday intervals and provisional extension from the last Final Bulletin B
value based on a combination of the series presented in section 6. What is the
degree of smoothing?
Section 3: Fiveday normal values of x, y, UT1UTC, dDy, and dDe (EOP(IERS) C02), and their uncertainties
and provisional extension from the last Final Bulletin B value based on a
combination of the series of section 6.
New class of robust MHuber estimators is used in the analysis
procedures (Bougeard et al., 2000).
Section 4: Smoothed values of DR and OmegaR, with the
same degree of smoothing as UT1RUTC.
Section 5: Information on the time scales and
announcement of the leap seconds.
Section 6: Average precision of the
individual series contributing to the combination and their agreement with the
combination.
VII.
INDIVIDUAL SERIES CONTRIBUTING TO IERS BULLETINS A AND B, JANUARY 2004
Table
2 gives the estimated accuracy with respect to IERS C04 of these series over 20032004
after removal of systematic variations, mainly a bias. The IERS C04 series is maintained by the IERS
Earth Orientation Centre (see EOP Combined Series at http://hpiers.obspm.fr/eoppc/
for details).
Table 2: Estimated accuracies of individual solutions entering the
combined solutions in 20032004.




Estimated uncertainties 

Individual solutions 



Time 
Terrestrial
Pole 
UT1
LOD 
Celestial
Pole 





0.001" 
0.0001s 
0.001" 
VLBI  24
h 







EOP
(AUS) 
01 
R 
01 
34d 
0.20 
0.05 
0.12 
EOP
(BKG) 
03 
R 
04 
14d 
0.22 
0.05 
0.15 
EOP
(GSFC) 
03 
R 
06 
14d 
0.16 
0.04 
0.10 
EOP
(IAA) 
03 
R 
04 
14d 
0.14 
0.04 
0.08 
EOP
(MAO) 
03 
R 
01 
14d 
0.21 
0.05 
0.17 
EOP
(SPBU) 
03 
R 
03 
34d 
0.22 
0.05 
0.13 
EOP
(USNO) 
03 
R 
04 
14d 
0.15 
0.04 
0.13 








VLBI
 Intensive 







EOP (BKG) 
03 
R 
02 
13 d 

0.13 

EOP (GSFC) 
03 
R 
05 
13 d 

0.12 

EOP (IAA) 
03 
R 
03 
13 d 

0.13 

EOP (SPBU) 
02 
R 
01 
13 d 

0.14 









Satellite Laser
Tracking 
king 






EOP (ASI) 
03 
L 
02 
1d 
0.30 
2.33 

EOP (CSR) 
95 
L 
01 
3d 
0.66 
1.15 

EOP (DUT) 
98 
L 
01 
3d 
0.56 


EOP (IAA) 
02 
L 
02 
1d 
0.27 
0.27 * 0.13 

EOP (MCC) 
97 
L 
01 
1d 
0.30 
0.48 









GPS 







EOP (CODE) 
98 
P 
01 
1d 
0.06 
0.26 

EOP (EMR) 
96 
P 
03 
1d 
0.10 
0.31 

EOP (ESOC) 
96 
P 
01 
1d 
0.13 
0.25 

EOP (GFZ) 
96 
P 
02 
1d 
0.09 
0.29 

EOP (IAA) 
01 
P 
01 
1d 
0.24 
0.37 

EOP (JPL) 
96 
P 
03 
1d 
0.08 
0.48 

EOP (NOAA) 
96 
P 
01 
1d 
0.25 
0.49 

EOP (SIO) 
96 
P 
01 
1d 
0.10 
0.32 

* The satellite techniques provide information on the rate of change of
Universal Time contaminated by effects due to unmodelled orbit node motion.
VLBIbased results have been used to minimize drifts in UT estimates
VIII. DISTRIBUTION OF THE PUBLICATIONS
A.
IERS Rapid Service/Prediction Centre, at U.S. Naval Observatory:
BULLETIN A
By 0h UTC of Friday of each week via
email distribution:

email subscription (contact: ser7@maia.usno.navy.mil)

World Wide Web (http://maia.usno.navy.mil/)

Anonymous ftp (ftp://maia.usno.navy.mil/ser7)
By about 17:30h UTC daily via anonymous
ftp:

World Wide Web (http://maia.usno.navy.mil/)

Anonymous ftp
(ftp://maia.usno.navy.mil/ser7)
B.
IERS Earth Orientation Centre, at Paris Observatory:

email (contact: iers@obspm.fr)

World Wide Web (http://hpiers.obspm.fr/eoppc/)

Anonymous ftp (hpiers.obspm.fr or 145.238.100.28)
BULLETIN B
Updated at the beginning of each month

World Wide Web

Anonymous ftp
(directory iers/bul/bulb)

airmail
William Wooden Daniel
Gambis
Director Director
IERS Rapid Service/Prediction Centre IERS
Earth Orientation Centre
wooden.william@usno.navy.mil daniel.gambis@obspm.fr
GLOSSARY
BIH Bureau
International de l'Heure
BIPM Bureau
International des Poids et Mesures
BKG Bundesamt fuer kartographie und geodaesie
CEP Celestial
Ephemeris Pole
CCIR International
Radio Consultative Committee
CIO Conventional
International Origin
CODE Center
for Orbit Determination in Europe
CGS Space
Geodesy Center, Matera
CSR Center
for Space Research, University of Texas
DORIS Doppler
Orbit determination and Radiopositioning Integrate on Satellite
DUT Delft
University of Technology
EMR See
NRCan
EOP Earth
Orientation Parameters
ESOC European
Space Operations Center
GFZ GeoForschungsZentrum
GMST Greenwich
Mean Sidereal Time
GPS Global
Positioning System
GSFC Goddard
Space Flight Center
IAA Institute
of Applied Astronomy
IAG International
Association of Geodesy
IAU International
Astronomical Union
IERS International
Earth Rotation Service
ICRF IERS
Celestial Reference Frame
ICRS International
Celestial Reference System
IGS International
GPS Service for Geodynamics
IRP IERS
Reference Pole
IRM IERS
Reference Meridian
ITRF IERS
Terrestrial Reference Frame
ITRS International
Terrestrial Reference System
IVS International
VLBI Service
JPL Jet
Propulsion Laboratory
LLR Lunar
Laser Ranging
LOD Length
of day
LODR Length
of day corrected from zonal tides effects
MCC Russian
Mission Control Center
MJD Modified
Julian Day
NEOS National
Earth Orientation Service
NOAA National
Oceanic and Atmospheric Administration
NRCan Natural
Resources Canada, formerly EMR
OPA Observatoire
de Paris
SPBU St
Petersburg University
SLR Satellite
Laser Ranging
SI Système
International
SIO
Scripps Institution of Oceanography
TAI Temps
Atomique International
TCG Geocentric
Coordinate Time
TT Terrestrial
Time
USNO United
States Naval Observatory
UT1 Universal
time
UT1R Universal
time corrected for zonal tides effects
UTC Coordinated
Universal Time
VLBI Very
Long Baseline Interferometry
REFERENCES
Aoki, S., Guinot, B.,
Kaplan, G.H., Kinoshita, H., McCarthy, D.D., Seidelmann, P.K., 1982: Astron.
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