[IGSMAIL-0496] GPS polar motion biases after adoption of ITRF92

[Martine]

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IGS Electronic Mail      Fri Feb 18  7:07:47 PST 1994      Message Number 0496
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Author: Martine Feissel, IERS/CB
Subject: GPS polar motion biases after adoption of ITRF92

Subject: GPS polar motion biases relative to IERS, 
         before and after the adoption of ITRF92.
 
We give hereafter mean differences and rms residuals of the GPS
series of polar motion before and after 1994 January 2, when the
ITRF92 coordinates and a new list of fixed sites were adopted by 
the Analysis Centres (except NOAA, according to our understanding).

The IERS series of polar motion referred to is the IERS/CB solution,
CORRECTED FOR THE PREDICTED BIAS AND SLOPES given in the 1992 IERS
Annual Report (p.II-17). The purpose of these corrections is to bring 
the IERS EOP time series into agreement with the ITRF92 positions and 
velocities. The uncertainty of the predicted correction is about 0.5 mas. 
The biases of the GPS series after 2 January 1994 (line 2) are thus 
expected to be consistent with zero within +/- 0.5 mas. The largest
bias found is 0.6 mas, an encouraging information on the level at which
internal consistency is controled, both in the 1992 IERS A.R. computations 
and in the GPS Analysis Centres ones. The largest mean differences between
two GPS series are 0.6 mas in X and 1.0 mas in Y.



GPS EOP time series - IERS/CB, all referred to ITRF92.    Unit: 0.001"
----------------------------------------------------------------------
                          X                               Y
Centre           bias           wrms             bias           wrms
     Period          uncert.   resid.                uncert.  resid.
----------------------------------------------------------------------
CODE	1	 0.45	0.04	0.42		-0.17	0.04	0.37
	2	 0.01	0.07	0.42		-0.62	0.05	0.27

EMR	1	 1.18	0.05	0.51		-0.48	0.05	0.50
	2	 0.60	0.10	0.60		 0.36	0.09	0.54

ESOC	1	 0.94	0.05	0.46		-0.14	0.05	0.44
	2	 0.07	0.07	0.48		-0.12	0.04	0.28
  
JPL	1	 0.52	0.05	0.45		-0.18	0.04	0.36
	2	 0.06	0.07	0.44		-0.30	0.07	0.44
 
GFZ	1	 0.55	0.03	0.31		-0.95	0.03	0.24
	2	 0.41	0.08	0.46		-0.23	0.05	0.29
 
NOAA	1	-0.42	0.07	0.63		-0.56	0.10	0.94
	3	-0.49	0.14	0.87		-0.86	0.12	0.75

SIO	1	 1.90	0.05	0.46		-0.81	0.07	0.66
	2	 0.61	0.12	0.64		 0.41	0.08	0.45
-----------------------------------------------------------------------  
Periods considered:
                      1: Oct-Dec 1993, before adoption of ITRF92
                      2: from 1994 Jan 2, after adoption of ITRF92,
                         all results available as of Feb 14.
                      3: from 1994 Jan 2, without adoption of ITRF92,
                         all results available as of Feb 14.
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