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	Gazette IERS Gazette IERS Gazette IERS Gazette IERS Gazette 

	No 03  08 JULY 1996
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                                IERS ANNOUNCEMENT
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                  THE INTERNATIONAL EARTH ROTATION SERVICE (IERS)
                    WILL REVISE ITS EARTH ORIENTATION SERIES 
                                ON 1 JANUARY 1997
                                                        
	
	The current series of IERS Earth Orientation Parameters (EOP) provide 
the transformation between the International Celestial Reference Frame (ICRF) 
and the International Terrestrial Reference Frame (ITRF)  with an accuracy not 
better than 1 milliarcsecond (mas), corresponding to 3 cm on the surface of 
the Earth, and a defect in the definition of universal time with an 18 year 
period and 3 mas amplitude that will be equal to zero at the beginning of 1997.

	The precision of the techniques contributing to IERS earth orientation
determinations: VLBI, GPS, SLR and DORIS, has been demonstrated to be at the
level of 1 cm (0.3 mas). Based on the results of its analyses, the IERS decided 
to bring the consistency of its EOP series with the International  Reference 
Frames to this level of accuracy.

	The change on 1 January 1997 will consist in 
	
	- a step smaller than 2 mas in x, y, UT1-TAI,
	- a time-linear correction smaller than 0.3 mas/year to x, y, UT1-TAI,
	  with reference epoch at the date of change,
	- the adoption of the more complete definition of UT1.
	
	All IERS EOP results (Bulletin A, Bulletin B,...) for epochs starting 
with 1 January 1997, 0h UT (MJD=50449.0) will be expressed in the new EOP 
system. All past series will be recomputed in the new system and made 
available by the usual means (electronic access, communication on request).
	
	The numerical values of the change are currently being finalized.
They will be distributed by 15 November 1996 on the same mailing lists as
this announcement. Requests for additional addresses should be sent to

                             iers@obspm.fr