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Combined Earth Rotation Parameter solution consistent with the 
International Terrestrial Reference Frame (ITRF) 2020 -version v3 

C04 2020 v3 solution
Started on 2025, June 5
Stopped on 2026, February 5

See also https://hpiers.obspm.fr/iers/eop/eopc04/updateC04.txt   
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Combined Earth Rotation Parameter solution consistent with the International Terrestrial Reference Frame (ITRF) 2020 

Features: 

1) Contain daily values of 8 Earth Rotation parameters with their formal errors: 

- Pole coordinates x, y (")
- UT1 - UTC (ms)
- Celestial pole offsets dX, dY or dPsi, dEps (")
- Pole coordinate rates xrt, yrt ("/day)
- Lenght of day offset LOD   (ms)

2) Download from https://hpiers.obspm.fr/iers/eop/eopc04/

5 options with a new format since 2023, February 14:
 
    i) eopc04.1962-now 	                 : sampled values at  0hUT /     dX, dY IAU 2006/2000A 
   ii) eopc04.dPsi_dEps.1962-now         :                    0hUT / dPsi, dEps IAU 2006/2000A  
  iii) eopc04.12h.1984-now               :                   12hUT /     dX, dY IAU 2006/2000A  
   iv) eopc04.dPsi_dEps.12h.1984-now     :                   12hUT / dPsi, dEps IAU 2006/2000A  
    v) eopc04.dPsi_dEps.IAU1980.1962-now :                    0hUT / dPsi, dEps IAU 1980

The former format with the file "eopc04_IAU2000.62-now" is maintained (without xrt and yrt parameters) : 
	
   vi) eopc04_IAU2000.62-now             :                    0hUT /     dX, dY IAU 2000 

3) Alignement with ITRF and corresponding updates 

- From 1/1/1962 to 31/12/1984, ERP values of those of the C0414 solution consistent with ITRF 2014

- From 1/1/1994 to 31/12/2020 the 12hUT values of the pole coordinates x,y and of their rates xrt and yrt 
are taken equal to the values obtained for the ITRF 2020 solution. 

- From 1/1/2021 to 24/2/2024 x,y, xrt, yrt are taken (12h values) or interpolated (0h values) from 
the ITRF2020-u2023 solution (https://itrf.ign.fr/ftp/pub/itrf/itrf2020-u2023/ITRF2020-u2023_EOP-F1.DAT).
Update effective on June 5, 2025. Former solution put in repository ../eopc04_20_v2. 

- From 25/2/2024, x,y, xrt, xyrt are derived by a weighted combination of 
IVS Quaterly/Rapid, IGS Final/Rapid, ILRS series 


4) Vondrak combined smoothing:  
    from 1/1/1984  for UT1 and LOD 
    from 25/2/2024 for x,y and ther rates 

5) Calibration of the formal uncertainties of the input individual ERP series according to the dispersion 
with other kindred series        

6) Removal of systematic bais / annual terms with respect to ITRF 2020 solution prolongated 
until the current year (x,y) and IVS Final (UT1, dX, dY) 
 
7) Centers contributing to 

x, y       : ITRF 2020 + extension (1994-2024), IGS F (2024-from 1 to 3 months before the current date), ILRS (2024-), IDS (2024-), IVSR (up to the last 3 months)
UT1        : IVSF-quaterly (1984-from 1 to 3 months before the current date), IVSR (up to the last 3 months), IAA Intensive, USNO Intensive, BKG Intensive
dX, dY     : IVSF-quaterly (1984-up to 3 months before the current date), IVSR (up to the last 3 months)
xrt, yrt   : ITRF 2020 + extension (1994-2024), IGS F quaterly (2024-from 1 to 3 months before the current date), IGS R (up to the last 3 months)
LOD        : IGS F (1998-), IGS-R (up to the last 3 months), CODE (current year)