INTERNATIONAL EARTH ROTATION SERVICE (IERS)
SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE
December 1992
EXPLANATORY SUPPLEMENT
TO IERS BULLETINS A AND B
IERS Bulletins A and B provide the users with 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 weekly; the standard
solution is given monthly in Bulletin B. The Annual Report, issued six
months after the end of each year, 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 Sub-
Bureau for Rapid Service and Predictions at U.S.Naval Observatory,
Washington; Bulletin B and the Annual Report are issued by the Central
Bureau, at Paris Observatory.
Bulletins A and B are meant for rapid service and standard use. For
scientific and long term analyses of the Earth's rotation, users are
advised to request the long term homogeneous series maintained by the
Central Bureau from 1846 (x, y), 1962 (UT), and 1981 (dPsi, dEpsilon) to
the current date.
THE IERS REFERENCE SYSTEM
The IERS REFERENCE System is composed of two parts: the IERS
standards and the IERS reference frames.
IERS STANDARDS
The IERS standards (McCarthy, 1992) are a set of constants and
models used by the IERS Analysis Centres for Very Long Baseline
Interferometry (VLBI), Lunar and Satellite Laser Ranging (LLR, SLR),
tracking of Global Positioning System satellites (GPS), and by the
Central Bureau 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 IAG conventional ones.
The models represent, in general, the state of the art in the field
concerned. VLBI and LLR observations have shown that there are
deficiencies in the IAU 1976 Precession and in the IAU 1980 Theory of
Nutation; however, these models are kept as a part of the IERS
standards, and the observed differences with respect to the conventional
celestial pole position defined by the models are monitored and reported
by the IERS.
IERS REFERENCE FRAMES
The IERS reference frames consist of the IERS Terrestrial Reference
Frame (ITRF) and IERS Celestial Reference Frame (ICRF); both frames are
realized through lists of coordinates of fiducial points, terrestrial
sites or compact extragalactic radio sources. The most recent
realizations of the ITRF and the ICRF are published in the IERS Annual
Report for 1991 and in IERS Technical Note No 12.
Terrestrial frame
The origin, the reference directions and the scale of ITRF are
implicitly defined by the coordinates adopted for the primary sites. The
origin of the ITRF is located at the center of mass of the Earth with an
uncertainty of +/-10cm.The unit of length is the metre (SI). The IERS
Reference Pole (IRP) and Reference Meridian (IRM) are consistent with
the corresponding directions in the BIH Terrestrial System (BTS) within
+/-0.005". The BIH reference pole was adjusted to the Conventional
International Origin (CIO) in 1967; it was then kept stable
independently until 1987. The uncertainty of the tie of the IRP with the
CIO is +/-0.03".
(For more information please see itrf91.guide).
Celestial frame
In a manner similar to the terrestrial frame, the directions of the
axes of the ICRF are defined by the coordinates adopted for the primary
radio sources. The origin of the ICRF is at the barycentre of the solar
system. The direction of the polar axis is the one given for epoch J2000
by the IAU 1976 Precession and the IAU 1980 Theory of Nutation. The
origin of right ascensions is in agreement with that of the FK5 within
+/-0.04".
(For more information please see icrf91.guide).
THE EARTH ORIENTATION PARAMETERS
The IERS Earth Orientation Parameters (EOP) are the parameters which
describe the rotation of the ITRF to the ICRF, in conjunction with the
conventional precession/nutation model. They model the unpredictable
part of the Earth's rotation.
1. x, and y are the coordinates of the Celestial Ephemeris Pole
(CEP) relative to the IRP, the IERS Reference Pole. The CEP differs
from the instantaneous rotation axis by quasi-diurnal terms with
amplitudes under 0.01" (see Seidelmann, 1982). The x-axis is in the
direction of IRM, the IERS Reference Meridian; the y-axis is in the
direction 90 degrees West longitude.
2. UT1 is related to the Greenwich mean sidereal time (GMST) by
a conventional relationship (Aoki et al., 1982); it gives access to
the direction of the IRM in the ICRF, reckoned around the CEP axis.
It is expressed as the difference UT1-TAI or UT1-UTC.
TAI is the atomic time scale of BIPM; its unit interval is
exactly one SI second at sea level. The origin of TAI is such that
UT1-TAI is approximately 0 on 1958 January 1. The instability of TAI
is about 6 orders of magnitude smaller than that of UT1.
UTC is defined by the CCIR Recommendation 460-4 (1986). It
differs from TAI by an integral number of seconds, in such a way
that UT1-UTC stays smaller than 0.9s in absolute value. The decision
to introduce a leap second in UTC to meet this condition is the
responsability of the IERS. According to the CCIR Recommendation,
first preference is given to the opportunities at the end of
December and June, 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.
DUT1 is the difference UT1-UTC expressed with a precision of
+/-0.1s, which is broadcast with the time signals. The changes in
DUT1 are decided by the IERS.
UT2 can be derived from UT1 by adding the following conventional
annual and semi annual terms.
UT2-UT1 = 0.0220sin(2*3.141593*t) - 0.0120cos(2*3.141593*t)
- 0.0060sin(4*3.141593*t) + 0.0070cos(4*3.141593*t),
the unit being the second and t being the date in besselian years.
t = 2000.000 + (MJD - 51544.03) / 365.2422.
The difference between the astronomically determined duration of the
day (D) and 86400s of TAI, is also 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 units of 0.01ms.
UT1, hence D and Omega, are subject to variations due to zonal
tides. The model which is a part of IERS Standards 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 short-term part of the model, i.e., the 41
components with periods under 35 days. UT1R-UT1 is smaller
than 2.5ms in absolute value.
3. dPsi, dEpsilon are the offsets in longitude and in obliquity
of the celestial pole with respect to its position defined by the
conventional IAU precession/nutation. A FORTRAN function for
computing the corresponding effect on dPsi and dEpsilon is available
from the Central Bureau on request. An evaluation of observations
from 1980 through early 1991 listing corrections to the IAU
precession/nutation is given by McCarthy and Luzum (1991a).
THE DATA ANALYSIS
The data analysis which yields the values of the EOP published in
Bulletins A and B includes several steps, which are summarized below.
1. Observations by the VLBI, LLR, GPS and SLR networks.
2. Analyses (quick-look and refined) by the IERS Analysis
Centres. The quick-look results are transmitted weekly in parallel
to the Sub-Bureau for Rapid Service and Predictions to contribute to
Bulletin A, and to the Central Bureau to contribute to Bulletin B.
The refined results are transmitted yearly to the Central Bureau.
3. General adjustment of ICRF, ITRF and EOP by the Central
Bureau, based on the refined results. This adjustment, described in
the Annual Report (part II), provides the basis for determining the
systematic corrections to be added to the individual series for the
following year in order to bring them into the IERS Reference
System; these cor- rections are used in step 5. The general results
are published in the Annual Report.
4. Determination of EOP by the Sub-Bureau for Rapid Service and
Predictions in the form of smoothed solutions at one-day 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 two to five days between the date of publication and the last
available date with estimated EOP. The details of the procedure are
outlined in McCarthy and Luzum (1991b).
5. Determination of EOP by the Central Bureau in the form of normal
values at five- day intervals and smoothed solutions at one-day and
five-day intervals. This involves the application of the systematic
corrections determined in step 3 and statistical weighting. 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.
6. Prediction of the EOP. Bulletins A and B provide predictions of
the EOP for up to ninety days. Details of the procedure used in
Bulletin A are given in McCarthy and Luzum (1991c).The
predictions use similar algorithms, based on seasonal filtering and
autoregressive processing for x, y, UT1 and on an approximate
modelled correction for the celestial pole offsets. Their
performances are given in Table 1.
Table 1- Precision of the various solutions. The accuracy of the tie to
the IERS System is given in eop90c04.guide.
-----------------------------------------------------------------------
Solutions ! terr.pole UT celest.pole
! 0.001" 0.0001s 0.001"
-----------------------------------------------------------------------
Bulletin A daily (1) ! 0.7 0.6 0.3
prediction (2) 10d ! 4.1 15. 0.4
40d ! 12. 70. 0.4
90d ! 21. 143. 0.4
!
Bulletin B !
smoothed (1)1-d, 5-d ! 0.6 0.6 0.5
raw (1) 5-d ! 0.4 0.4 0.6
prediction (1) 10d ! 2.0 14. 1.6
40d ! 6.5 60. 3.5
Notes.(1) Based on 1990-91 data.
(2) Based on tests of predictions using data over 1985-1991.
CONTENTS OF BULLETINS A AND B
BULLETIN A (Weekly)
Section 1 : General information including key definitions, and
the most recently adopted values of DUT1 and TAI-UTC.
Section 2 : Plots of recent variations in UT1-UTC and polar motion.
Section 3 : Observed values of EOP contributed by participants in
the IERS. This includes the most recent VLBI, SLR and LLR data
received by the Sub-Bureau for Rapid Service and Predictions.(see
Table 3).
Section 4 : Quick-look daily estimates of the EOP, determined
by smoothing the observed data, with accuracies as shown in Table 1.
The transfer function of the smoothing process is given in Annual
Report 1991, p. III-4. The results are published with a delay of
about two to five days between the date of publication and the last
available date with estimated EOP.
Section 5 : Predictions of x, y, UT1-UTC up to ninety days
following the last day of data in Section 4 and predictions at
monthly intervals up to a year in advance.
Section 6 : Observations of celestial pole offsets, smoothed
daily values, and predictions of celestial pole offsets.
BULLETIN B (Monthly)
Section 1 : Smoothed values of x,y, UT1R-UTC, UT1R-TAI, dPsi,
dEpsilon, at five-day interval based on a combination of the series
of section 6. Final Bulletin B values over one month and provisional
extension over the next four months. The cutoffs of the smoothing
algorithms is given in Table 2. The smoothings are based on the
Vondrak (1977) algorithm. (see also Feissel and Lewandowski,1984).
Table 2- Caracteristics of the smoothing adopted for the Bulletin B.
-----------------------------------------------------------------------
Period ! 88-89 89-Aug92 Aug92-present
---------------!-------------------------------------------------------
X ! 12d 8d 3d
Y ! 12d 8d 3d
UT ! 12d 5d 3d
dPsi*sin(eps) ! 8d 8d
dEps ! 8d 8d
Section 2 : Daily interpolation of x, y, UT1-UTC, UT1-UT1R, D,
dPsi, and dEpsilon, consistent with section 1.
Section 3 : Five-day normal values of x, y, UT1-UTC, dPsi,
dEpsilon, and their uncertainties, based on a combination of the
series of section 6.
Section 4.: Smoothed values of DR and OmegaR, with the same
degree of smoothing than for UT1R-UTC (see Table 2).
Section 5 : Current values of UTC-TAI and DUT1, reproducing
IERS Bulletins C and D.
Section 6.: Summary of the contributed EOP series, giving their
average precision and average agreement with the current
Bulletin B solution.
Section 7 : Data of IERS analysis centers. In this section, the
original results received from the IERS analysis centers and used
for the solution listed in sections 1 to 3 are reproduced. These
results are those which are available one to five weeks after the
observation dates. Updated results received later are stored, but as
a general rule, they are not printed in Bulletin B. The updated
series are available from the Central Bureau of IERS on request
(computer files, tapes and printouts). The series used in October
1992 are listed in Table 3; in addition, values of universal time
derived from the axial AAM (analysed and predicted) provided by
UKMO and ECMWF are used for very recent dates.
Table 3- Individual series contributing to IERS Bulletins A and B
October 1992. The formal uncertainties are those which are
reported by the contributors. They are used in the combinations for
Bulletins A and B after being calibrated by statistical assessment.
-----------------------------------------------------------------------
! sampling formal uncertainties
Series ! time terr.pole UT celest.pole
! 0.001" 0.0001s 0.001"
-----------------------------------------------------------------------
EOP(JPL) 91 R 01 ! 0.1-13d 1.3 1.4
EOP(NGS) 88 R 01 ! 7d 0.3 0.2 0.4
EOP(NGS) 88 R 02 ! 1-2d 0.6
EOP(USNO) 91 R 02 ! 7d 0.3 0.2 0.3
EOP(UTXMO)91 M 01 ! 0.1-30d 3.0
EOP(CODE) 92 P 04 ! 1d 0.1
EOP(CSR) 91 P 02 ! 1d 0.2
EOP(EMR) 92 P 04 ! 1d O.2
EOP(ESOC) 92 P 02 ! 1d 0.3
EOP(GFZ) 92 P 02 ! 1d 0.4
EOP(JPL) 92 P 03 ! 1d 0.2
EOP(SIO) 92 P 03 ! 1d 0.2
EOP(CSR) 91 L 01 ! 3d 0.7 0.6
EOP(DUT) 91 L 02 ! 5d 0.2
DISTRIBUTION OF BULLETINS A AND B
Bulletin A (Sub-Bureau for Rapid Service and Prediction, at U.S.
Naval Observatory)
By 0h UTC of Friday of each week :
- airmail
- GE Mark 3 (RC28 Catalog, contact : EARTH)
- EARN/BITNET (INTERNET)
(contact : EOP@USNO01.USNO.NAVY.MIL)
- NSI/DECNET (contact : 6899::EOP)
- NEOS Bulletin Board (202 653 0597)
Bulletin B (Central Bureau, at Paris Observatory)
Between the 1st and the 6th day of each month:
- SPAN (contact : IAPOBS::IERS)
- EARN/BITNET (contact : iers@friap51)
- INTERNET (contact : iers@friap51.bitnet)
- GE Mark3 (RC28 Catalog, contact : IERS-CB)
- airmail
Martine Feissel Dennis D. McCarthy
Director Head
Central Bureau of IERS IERS Sub-Bureau for Rapid
Service and Predictions
------------------------------------------------------------------------
GLOSSARY
AAM Atmospheric Angular Momentum
BIH Bureau International de l'Heure
BIPM Bureau International des Poids et Mesures
CEP Celestial Ephemeris Pole
CERGA Centre d'Etudes et de Recherches Geodynamiques
et Astronomiques
CCIR International Radio Consultative Committee
CIO Conventional International Origin
CODE Center for Orbit Determination in Europe
CSR Center for Space Research, University of Texas
DUT Delft University of Technology
ECMWF European Centre for Medium-range Weather Forecasting
EMR Energy Mines and Ressources
EOP Earth Orientation Parameters
ESOC European Space Operations Centre
GMST Greenwich Mean Sidereal Time
GFZ GeoForschungsZentrum
IAG International Association of Geodesy
IAU International Astronomical Union
IERS International Earth Rotation Service
ICRF IERS Celestial Reference Frame
ITRF IERS Terrestrial Reference Frame
IRP IERS Reference Pole
IRM IERS Reference Meridian
ILS International Latitude Service
LLR Lunar Laser Ranging
IRIS International Radio Interferometric Surveying
JPL Jet Propulsion Laboratory
NEOS National Earth Orientation Service
NGS National Geodetic Survey
SLR Satellite Laser Ranging
SI Systeme International
SIO Scripps Institute of Oceanography
TAI Temps Atomique International
TDT Terrestrial Dynamical Time
UKMO U.K. Meteorological Office
USNO United States Naval Observatory
UTC Coordinated Universal Time
UTXMO Dept. of Astronomy. The University of Texas at Austin.
VLBI Very Long Baseline Interferometry
REFERENCES
Aoki, S.,Guinot, B., Kaplan, G.H., Kinoskita, H., McCarthy, D.D.,
Seidelmann, P.K., 1982: Astron.and Astrophys.105, 1.
Feissel, M. and Lewandowski, W., 1984: Bull.Geod.58, 464.
McCarthy, D.D. (ed.), 1989: IERS Technical Note No 3. Observatoire
de Paris.
McCarthy, D.D. and Luzum, B.J., 1991a: Astron. J., 102, 1989.
McCarthy, D.D. and Luzum, B.J., 1991b: Bull. Geod., 65, 22.
McCarthy, D.D. and Luzum, B.J., 1991c: Bull. Geod., 65, 18.
Seidelmann, P.K., 1982: Celest.Mech.,27, 79.
Vondrak, J., 1977: Bull. of the Astron. of Czechoslovaquia, 28, 84.
INTERNATIONAL EARTH ROTATION SERVICE (IERS)
SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE
March 1994
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 weekly; the standard solution
is given monthly in Bulletin B. The Annual Report, issued six months
after the end of each year, 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 Sub-Bureau for
Rapid Service and Predictions at the U.S. Naval Observatory, Washington;
Bulletin B and the Annual Report are issued by the Central Bureau , at
the Paris Observatory.
Bulletins A and B are meant for rapid service and standard use. For
scientific and long term analyses of the Earth's orientation, users
are advised to request the long term homogeneous series maintained by
the Central Bureau from 1846 (x, y), 1962 (UT), and 1981 (dPsi, dEpsilon)
to the current date.
THE IERS REFERENCE SYSTEM
The IERS REFERENCE System is composed of two parts : the IERS standards
and the IERS reference frames.
IERS STANDARDS
The IERS standards (McCarthy, 1992) are a set of constants and models
used by the IERS Analysis Centers for Very Long Baseline Interferometry
(VLBI), Global Positioning System (GPS), Lunar and Satellite Laser
Ranging (LLR, SLR), and by the Central Bureau 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 IAG conventional ones.
The models represent, in general, the state of the art in the field
concerned. VLBI and LLR observations have shown that there are
deficiencies in the IAU 1976 Precession and in the IAU 1980 Theory of
Nutation; however, these models are kept as a part of the IERS
standards, and the observed differences with respect to the conventional
celestial pole position defined by the models are monitored and reported
by the IERS.
IERS REFERENCE FRAMES
The IERS reference frames consist of the IERS Terrestrial Reference
Frame (ITRF) and IERS Celestial Reference Frame (ICRF); both frames
are realized through lists of coordinates of fiducial points, terrestrial
sites or compact extragalactic radio sources. Recent realizations of the
ITRF and the ICRF are published in the IERS Annual Report. Details on
the ITRF92 are given in IERS Technical Note NO 15 and NO 7 respectively.
Terrestrial frame
The origin, the reference directions and the scale of ITRF are implicitly
defined by the coordinates adopted for the primary sites. The origin of
the ITRF is located at the center of mass of the Earth with an
uncertainty of +/-5cm.The unit of length is the metre (SI). The IERS
Reference Pole (IRP) and Reference Meridian (IRM) are consistent with
the corresponding directions in the BIH Terrestrial System (BTS)
within +/-0.005". The BIH reference pole was adjusted to the Conventional
International Origin (CIO) in 1967; it was then kept stable
independently until 1987. The uncertainty of the tie of the IRP with the
CIO is +/-0.03".
Celestial frame
In a manner similar to the terrestrial frame, the directions of the axes
of the ICRF are defined by the coordinates adopted for the primary radio
sources. The origin of the ICRF is at the barycenter of the solar system.
The direction of the polar axis is the one given for epoch J2000.0 by
the IAU 1976 Precession and the IAU 1980 Theory of Nutation. The origin
of right ascensions is in agreement with that of the FK5 within +/-0.04".
THE EARTH ORIENTATION PARAMETERS
The IERS Earth Orientation Parameters (EOP) are the parameters which
describe the rotation of the ITRF to the ICRF, in conjunction with the
conventional precession/nutation model. They model the unpredictable
part of the Earth's rotation.
1. x and y are the coordinates of the Celestial Ephemeris Pole (CEP)
relative to the IRP. The CEP differs from the instantaneous
rotation axis by quasi-diurnal terms with amplitudes under 0.01"
(see Seidelmann, 1982). The x-axis is in the direction of IRM; the
y-axis is in the direction 90 degrees West longitude.
2. UT1 is related to the Greenwich mean sidereal time (GMST) by a
conventional relationship (Aoki et al., 1982); it gives access to
the direction of the IRM in the ICRF, reckoned around the CEP
axis. It is expressed as the difference UT1-TAI or UT1-UTC.
TAI is the atomic time scale of the BIPM; its unit interval is
exactly one SI second at mean sea level. The origin of TAI is
such that UT1-TAI is approximately 0 on 1958 January 1. The
instability of TAI is about six orders of magnitude smaller than
that of UT1.
UTC is defined by the CCIR Recommendation 460-4 (1986). It differs
from TAI by an integral number of seconds, in such a way that
UT1-UTC stays smaller than +/- 0.9s in absolute value. The decision
to introduce a leap second in UTC to meet this condition is the
responsability of the IERS. According to the CCIR Recommandation,
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.
DUT1 is the difference UT1-UTC expressed with a precision of
+/-0.1s, which is broadcast with the time signals. The changes in
DUT1 are decided by the IERS.
UT2 can be derived from UT1 by adding the following conventional
annual and semi-annual terms.
UT2-UT1 = 0.0220sin(2*3.141593*t) - 0.0120cos(2*3.141593*t)
- 0.0060sin(4*3.141593*t) + 0.0070cos(4*3.141593*t),
the unit being the second and t being the date in besselian years.
t = 2000.000 + (MJD - 51544.03) / 365.2422.
Tables of UT2-UT1 are available from the Central Bureau of the IERS
on request.
The difference between the astronomically determined duration of
the day (D) and 86400s of TAI, is also 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 units of ms.
UT1, hence D and Omega, are subject to variations due to zonal tides.
The model which is a part of IERS Standards 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 short-term part of the model, i.e., the 41 components
with periods under 35 days. UT1R-UT1 is smaller than 2.5ms in
absolute value.
3. dPsi, dEpsilon are the offsets in longitude and in obliquity of
the celestial pole with respect to its position defined by the
conventional IAU precession/nutation. Corrections to the IAU
models have been published ( Herring et al., 1991; McCarthy and
Luzum, 1991c; Zhu et al., 1990).
The EOP of Bulletins A and B are constent with the ITRF and ICRF
within +/-0.002". Corrections for improvins the consistency to
+/-0.0005" are given in the 1992 IERS Annual Report.
THE DATA ANALYSIS
The data analysis which yields the values of the EOP published in
Bulletins A and B includes several steps, which are summarized below.
1. Observations by the VLBI, LLR, SLR and GPS networks.
2. Analyses (quick-look and refined) by the IERS Analysis Centers. The
quick-look results are transmitted weekly in parallel to the
Sub-Bureau for Rapid Service and Predictions to contribute to
Bulletin A, and to the Central Bureau to contribute to Bulletin B.
The refined results are transmitted yearly to the Central Bureau.
3. General adjustment of ICRF, ITRF and EOP by the Central Bureau,
based on the refined results. This adjustment, described in the
Annual Report (part II), provides the basis for determining the
systematic corrections to be added to the individual series
for the following year in order to bring them into the IERS
Reference System; these corrections are used in step 5. The general
results are published in the Annual Report.
4. Determination of EOP by the Sub-Bureau for Rapid Service and
Predictions in the form of smoothed solutions at one-day 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 two to five days between the date of publication and the
last available date with estimated EOP. The details of the
procedure are outlined in McCarthy and Luzum (1991b).
5. Determination of EOP by the Central Bureau in the form of normal
values at five-day intervals and smoothed solutions at one-day and
five-day intervals. This involves the application of the systematic
corrections determined in step 3 and statistical weighting.
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.
6. Prediction of the EOP. Bulletins A and B provide predictions of
the EOP. Details of the procedure used in Bulletin A are given in
McCarthy and Luzum (1991c). The predictions use similar algorithms,
based on seasonal filtering and autoregressive processing for
x, y, UT1 and on an approximate modelled correction for the
celestial pole offsets. Their performances are given in Table 1.
Table 1- Precision of the various solutions. The accuracy which
includes the uncertainty of the tie to the IERS System can be
estimated by adding quadratically 0.0007" in terrestrial pole,
0.00012s in UT1, and 0.0005" in celestial pole.
----------------------------------------------------------------------
Solutions ! terr.pole UT celest.pole
! 0.001" 0.0001s 0.001"
----------------------------------------------------------------------
Bulletin A daily (1) ! 0.4 0.5 0.3
prediction (2) 10d! 3.5 15. 0.3
40d! 10. 64. 0.3
90d! 16. 117. 0.3
!
Bulletin B !
smoothed (1)1-d, 5-d! 0.5 0.5 0.5
raw (1) 5-d! 0.3 0.3 0.4
prediction (1) 10d! 2.1 4.0 0.4
40d! 31. 65. 0.9
Notes.
(1) Based on 1992-93 data.
(2) Based on data since 1990.
CONTENTS OF BULLETINS A AND B
BULLETIN A (Weekly)
General information including key definitions, and the most recently
adopted values of DUT1 and TAI-UTC.
Plots of recent variations in UT1-UTC and polar motion.
Observed values of EOP contributed by participants in the IERS.
This includes the most recent VLBI, SLR, LLR and GPS data received by
the Sub-Bureau for Rapid Service and Predictions.
Quick-look daily estimates of the EOP, determined by applying systematic
corrections and smoothing the observed data, with accuracies as shown in
Table 1.
The transfer function of the smoothing process is shown in Figure 1.
The results are published with a delay of about two to five days between
the date of publication and the last available date with estimated EOP.
Predictions of x, y, UT1-UTC daily up to ninety days following the last
day of data in Section 4 and predictions at monthly intervals up to a
year in advance.
Observations of celestial pole offsets, smoothed daily values, and
predictions of celestial pole offsets.
Figure 1. Transfer function of smoothings of Bulletin A and B
(Please see the paper version for the figure)
BULLETIN B (Monthly)
Section 1 : Five days sampling of section 2. Final Bulletin B values
over one month and provisional extension over the next
four months.
Section 2 : Smoothed values of x,y, UT1R-UTC, UT1R-TAI, dPsi, dEpsilon,
at one-day interval based on a combination of the series
of section 6. The transfer functions of the smoothing
algorithms are given in Figure 1. These smoothings were
adopted on August 1992 (Bulletin B 54) and are based on the
Vondrak (1977) algorithm, with degrees of smoothing
indicated in brackets (see also Feissel and Lewandowski,1984).
Section 3 : Five-day normal values of x, y, UT1-UTC, dPsi, dEpsilon, and
their uncertainties, based on a combination of the series
of section 6.
Section 4 : Smoothed values of DR and OmegaR, with the same degree of
smoothing as UT1R-UTC (see figure 1).
Section 5 : Current values of UTC-TAI and DUT1, reproducing IERS
Bulletins C and D.
Section 6 : This section gives the average precision of the individual
series contributing to the combination and their agreement
with the combination.
Section 7 (available only on the electronic and FTP version): Data of
IERS analysis centers.
Table 2- Individual series contributing to IERS Bulletins A and B,
January 1994. The formal uncertainties are those which are
reported by the contributors. They are used in the
combinations for Bulletins A and B after being calibrated
by statistical assessment.
-----------------------------------------------------------------------
!sampling formal uncertainties based on 1992-94 data
Series! time terr.pole UT celest.pole
! 0.001" 0.0001s 0.001"
-----------------------------------------------------------------------
EOP(JPL) 93 R 01!0.1-13d 1.0
EOP(NOAA) 93 R 04!7d 0.2 0.1 0.3
EOP(NOAA) 93 R 06!1-2d 0.3
EOP (OPA) 93 R 02!1d 0.2
EOP(USNO) 93 R 09!7d 0.2 0.1 0.3
EOP(UTXMO) 93 M 01!0.1-30d 3.8
EOP(CSR) 93 L 02!3d 0.6 0.5
EOP(DUT) 93 L 03!5d 0.2
EOP(CODE) 94 P 01!1d 0.1
EOP(EMR) 94 P 01!1d 0.2
EOP(ESOC) 94 P 01!1d 0.1
EOP (GFZ) 94 P 01!1d 0.1
EOP(JPL) 94 P 01!1d 0.2
EOP (NOAA) 93 P 01!1d 0.1
EOP(SIO) 94 P 01!1d 0.1
DISTRIBUTION OF BULLETINS A AND B
Bulletin A (Sub-Bureau for Rapid Service and Prediction, at U.S. Naval
Observatory)
By 0h UTC of Friday of each week :
- INTERNET (contact : EOP@USNO01.USNO.NAVY.MIL)
- NSI/DECNET (contact : 6899::EOP)
- NEOS Bulletin Board (202 653 0597)
- Anonymous FTP (maia.usno.navy.mil or 192.5.41.22)
- airmail
Bulletin B (Central Bureau, at Paris Observatory)
Between the 1st and the 6th day of each month:
- SPAN (contact : IAPOBS::IERS)
- INTERNET (contact : iers@iap.fr)
- Anonymous FTP (mesiom.obspm.fr or 145.238.2.21)
- airmail
Martine Feissel Dennis D. McCarthy
Director Head
Central Bureau of IERS IERS Sub-Bureau for Rapid Service
and Predictions
GLOSSARY
AAM Atmospheric Angular Momentum
BIH Bureau International de l'Heure
BIPM Bureau International des Poids et Mesures
CEP Celestial Ephemeris Pole
CERGA Centre d'Etudes et de Recherches Geodynamiques et Astronomiques
CCIR International Radio Consultative Committee
CIO Conventional International Origin
CODE Center for Orbit Determination in Europe
CSR Center for Space Research, University of Texas
DUT Delft University of Technology
ECMWF European Centre for Medium-range Weather Forecasting
EMR Department of Energy, Mining, and Resources
EOP Earth Orientation Parameters
ESOC European Space Operations Center
GFZ GeoForschungsZentrum
GMST Greenwich Mean Sidereal Time
GPS Global Positioning System
IAG International Association of Geodesy
IAU International Astronomical Union
IERS International Earth Rotation Service
ICRF IERS Celestial Reference Frame
ITRF IERS Terrestrial Reference Frame
IRP IERS Reference Pole
IRM IERS Rerence Meridian
ILS International Latitude Service
JPL Jet Propulsion Laboratory
LLR Lunar Lasr Ranging
NEOS National Earth Orientation Service
NOAA National Oceanic and Atmospheric Administration
SLR Satellite Laser Ranging
SI Systeme International
SIO Scripps Institution of Oceanography
TAI Temps Atomique International
TDT Terrestrial Dynamical Time
UKMO U.K. Meteorological Office
USNO United States Naval Observatory
UTC Coordinated Universal Time
UTXMO Dept. of Astronomy. The University of Texas at Austin.
VLBI Very Long Baseline Interferometry
REFERENCES
Aoki, S.,Guinot, B., Kaplan, G.H., Kinoshita, H., McCarthy, D.D.,
Seidelmann, P.K., 1982: Astron.and Astrophys.105, 1.
Feissel, M. and Lewandowski, W., 1984: Bull.Geod.58, 464.
McCarthy, D.D. (ed.), 1992: IERS Technical Note No 13.
Observatoire de Paris.
McCarthy, D.D. and Luzum, B.J., 1991a: Astron. J., 102, 1989.
McCarthy, D.D. and Luzum, B.J., 1991b: Bull. Geod., 65, 22.
McCarthy, D.D. and Luzum, B.J., 1991c: Bull. Geod., 65, 18.
Seidelmann, P.K., 1982: Celest.Mech.,27, 79.
Vondrak, J., 1977: Bull. of the Astron. Inst. of Czechoslovaquia, 28, 84.