EOP(IERS) C 01
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Last update: July 8 2024
Full update of CO1 data, which the pole coordinates are in better agreement with Conventional International Origin (CIO) over the period 1900-1906.
Former version presented a spurious shift over the interval 1900 - 1962, which has been removed subsequently.
Contact: Christian BIZOUARD
EOP(IERS) C 01 is a series of the earth Orientation Parameters given at 0.1
year interval (1846 - 1889) and 0.05 year over the interval 1890 to now.
This series is the basis of the IERS system for long-term studies. Nethertheless
it is updated regularly once per month, and encompasses the last 0.05 year interval.
EOP(IERS) C 01 is based on the following data:
1962 - now : EOP(IERS) C 04 14 solution of x, y, UT1-UTC, dPsi/dX, dEpsilon/dY
+ Vondrak smootihng (50% of the signal transfered at 50 days)
resulting from the following astrometric measurements:
- 1993 - now : space techniques VLBI, LLR, SLR and GNSS
- 1989 - 1992 : space techniques VLBI, LLR, SLR
- 1962 - 1979 : optical astrometry (BIH solutions), and space techniques starting with 1969 (LLR: UT)
and 1972 (Doppler: polar motion).
1900 - 1961 : Vondrak et al (1995) solution derived from optical astrometry
analyses the series give polar motion, and Universal Time (since 1956)
+ Gaussian filter at 0.05 year step.
1846 - 1899 : The solution derived by L.V. Rikhlova (Fedorov et al., 1976)
from three series of absolute declination programs (Pulkovo,
Greenwhich, Washington). The frequency band of the variations
kept encompasses only the annual and Chandler terms. The y
coordinate of the pole is missing from 1858.9 through 1860.9.
Before 1962 nutation is directly taken from the IAU 2000 model, meaning
celestial pole offsets / IAU 2000 model dX=dY =0, with an accuracy of 1 mas (the maximum offset observed today).
We also provide celestial pole offset Dpsi, dEps with respect to IAU 1980 precession-nutation model.
SOLUTIONS AVAILABLE: Two available formats
1) Special C01 format:
eopc01.1846-1899.dat : 1846-1899 / nutation respectively relative to IAU1980
eopc01.iau2000.1846-1899.dat : 1846-1899 / nutation respectively relative to IAU2000
eopc01.1900-now.dat : 1900-now / nutation respectively relative to IAU1980
eopc01.iau2000.1900-now.dat : 1900-now / nutation respectively relative to IAU2000
Format:
col1: date : Besselian year
col2, col3 : x pole, uncertainty (")
col4, col5 : y pole, uncertainty (")
col6, col7 : UT1-TAI, uncertainty, from 1956 (s)
col8, col9 : nutation offset dPsi wrt IAU1980 or dX wrt IAU 2000, uncertainty (")
col10,col11: nutation offset dEps wrt IAU1980 or dY wrt IAU 2000, uncertainty (")
Fortran: FORMAT(f10.2,4f10.6,2f11.7,4f10.6)
2) Common IERS format
eopc01.1846-now : 1846-now / nutation respectively relative to IAU1980
eopc01.iau2000.1846-now : 1846-now / nutation respectively relative to IAU2000
Contents: the same as in the case 1)
N.B.: before 1956 UT1-TAI values do not exist and are set at 99.99
before 1962 LOD values do not exist and are set at 99.99
PRECISION AND ACCURACY
The individual values are accompanied by uncertainties which attempt to
reflect their quality. For the IERS/BIH solutions, they are derived from the
scattering of the independant measurements contributing to each normal point,
with added variance taking into account possible systematic errors. For the
earlier period, they are based on the estimations given by Fedorov et al.
(1976), scaled to match the agreement woth the IERS/BIH solution over
1962-1968. In addition some isolated outliers are deweighted (uncertainty
multiplied by 3).
The following remarks can be made concerning the drift and the annual term
before 1962:
Trend: as a result of the Fedorov et al. treatment, any drift in polar
motion existing before 1900 is ignored in the series. For the period
starting with 1900, although no external evidence is available for
the pre-1972 polar motion, it should be mentionned that the low
frequency spectrum of polar motion both before and after the advent
of space techniques (giving the possibility of cross-checks) is that
pf random walk at a similar level.
N.B.: As it can be seen from the plot
http://hpiers.obspm.fr/iers/eop/eopc01/mean-pole.jpg, for the 1900 epoch
the C01 mean pole is shifted by about 0.1" from the CIO
(Conventional International Origin), meaning that C01 is not
consistent with the CIO system. Indeed CIO coincides with the mean pole of the 1900
epoch. This issue is curently under investigation.
Annual term: it is influenced by errors in nutation and local seasonal errors.
Comparisons of the Fedorov et al. solution with the IERS/BIH one over
1962 - 1968 suggest that the amplitude of the annual term is accurate
to +/- 0.03" over 1900 - 1962.
REFERENCES
- Fedorov,E.P., Korsun,A.A, Mayor,S.P., Pantschenko,N.I., Tarady,V.K., and
Yatskiv,Y.S. (1972), Dvizhenie polyusa Zemli s 1890.0 po 1969.0. Naukova
Dumka, Kiev. [English translation of the text available].
- Vondrak J., Ron C., Pesek I., Cepek A. (1995), Astron. and Astrophys.
297,899-906.
- Vondrak J., Ron C., Stefka V. (2010): Earth orientation parameters based on EOC-4
astrometric catalog, Acta Geodyn. Geomat.
- IERS Annual reports
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Recent changes:
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2024 July 7 : An xp outlier for 1869.8 / MJD 3989.492 (0.055680) has been replaced by the original value
published in Fedorov et al (1972). Error found by Zinoviy Malkin (Pulkovo Observatory).
2024 March 18: before 1962 LOD values do not exist and are set at 99.99
2024 February 20: before 1962 LOD values do not exist and are set at 99.99