Subject: [IGSREPORT-3] EARTH ORIENTATION Bulletin number 9 - 9 november 1992 -
From: IERS
Date: 11 NOV 1992 18:31:24

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IGS Electronic Report     11-NOV-1992 18:31:24       Message Number 3
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From:     IERS 
Subject:  EARTH ORIENTATION Bulletin number 9 - 9 november 1992 -
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                    IGS'92 EARTH ORIENTATION BULLETIN   9
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                                                          9 NOVEMBER 1992

Starting with IERS  Bulletin B58, issued early December 1992 and covering
October 1992, the GPS Earth Orientation Parameters will be introduced in
the computation of the Central Bureau of IERS. Section 6 of Bulletin B
will include statistics on the VLBI, LLR, GPS and SLR solutions received.
The present Earth Orientation Bulletin is the last one issued in support
to the IGS'92 campain.

COMPARISONS OF GPS, LLR, SLR AND VLBI EARTH ORIENTATION DETERMINATIONS

A paper version of this part, with plots, will be mailed to the IERS Analysis
Centres and to the IGS Processing Centres. Additional copies are available on
request.

GPS: TERRESTRIAL FRAME ORIENTATION FIXING

Various strategies are tested by the GPS Processing Centres for maintaining
the terrestrial frame orientation. The choices concern the nominal orientation
(ITRF90 or ITRF91), the site motion model used to transfer the coordinates at
the reference epoch, the number of fiducial  stations that are fixed, and the
source from which the fixed  coordinates are taken. We summarize in Table 1 our
understanding  of the terrestrial  frame  definitions according to the Centres
and to the time periods.

 Table 1 - GPS SOLUTIONS: TERRESTRIAL FRAME ORIENTATION
 ---------------------------------------------------------------------------
     Series             MJD        GPS    Nominal
   (IERS label)     from  to      weeks   refrnce    Source
 ---------------------------------------------------------------------------
 EOP(CODE) 92 P 04  48792-48923  650-668  ITRF91     IERS       (IGSMail 33)

 EOP(CSR)  92 P 01  48794-48870  650-660             CSR+GSFC   (IGSMail 62)

 EOP(EMR)  92 P 01  48838-48904  655-665  ITRF91     IERS       (IGSMAIL 90)
 EOP(EMR)  92 P 02  48901-48911  655-666  ITRF91     IERS       (IGSMAIL 90)

 EOP(ESOC) 92 P 01  48794-48912  650-666  ITRF91     IERS       (IGSMail 90)

 EOP(GFZ)  92 P 01  48794-48821  650-653  ITRF90     SIO       (01/91-05/92)
 EOP(GFZ)  92 P 02  48822-48918  654-667  ITRF90     SIO        (IGSMail 56)

 EOP(JPL)  92 P 01  48794-48821  650-653  ITRF90     JPL  (GIG'91+VLBI vel.)
 EOP(JPL)  92 P 02  48820-48918  654-667  ITRF91     IERS       (IGSMail 90)

 EOP(SIO)  92 P 03  48780-48918  648-667  ITRF90     SIO    (51 IGS'92 days)
--------------------------------------------------------------------------------

 VLBI, LLR, SLR, GPS EOP DETERMINATIONS: AGREEMENT WITH THE IERS SYSTEM

In this section, the VLBI, LLR, SLR, and GPS observations available over the
time period of the IGS'92 Campaign and its continuation (MJD 48779-48923)
are compared to the IERS series EOP(IERS) 90 C 04, which is a combination
of the series of Table 2.

  Table 2 - IERS OPERATIONAL SERIES OF EOP
  ------------------------------------------------------------------------
  Techn.      Series           Time       Time          EOP determined
                               span      interv.
  ------------------------------------------------------------------------
   VLBI  EOP(NOAA)  92 R 01     24 h     3/4 d     x, y,  UT1, dPsi, dEps
   VLBI  EOP(NOAA)  92 R 02      1 h     1/2 d            UT1
   VLBI  EOP(USNO)  92 R 03     24 h      7  d     x, y,  UT1, dPsi, dEps

   LLR   EOP(UTXMO) 92 M 02      1 h    0.1/30d           UT1

   SLR   EOP(CSR)   91 L 01     72 h      3  d     x, y, "UT1"
   SLR   EOP(DUT)   91 L 02    120 h      5  d     x, y, "UT1"
  ------------------------------------------------------------------------

The GPS series are those listed in Table 1. They give the x,y coordinates of
the
pole, except CODE, which gives a series of UT1 that is tied at the beginning of
the complete series to an a priori value,and the new EMR series, whith UT1 tied
to an a priori value at the beginning of each week.  The "UT1" determinations
obtained by the SLR Analysis Centre at DUT is left free, whereas in the CSR
SLR solution, it is tied to a VLBI solution for periods longer than about 60
days.

The  GPS  results are obtained from one-day observations of 16 to 18 satellites
in a network of 11 to 29 stations: 14-19 for CODE, 14-20 for CSR, 17-18 for EMR,
11-18 for ESOC, 22-27 for JPL, and 17-29 for SIO.

Most of the centres treat independently the successive daily arcs, the
exceptions being CODE (three-day overlapping arcs) and GFZ (two-day
overlapping arcs). The centres estimate the EOP at 12h UT.

Table 3 gives the differences of the VLBI, SLR,and GPS series with
EOP(IERS) 90 C 04 under the form of a constant bias, corrected for the predicted
value of the systematic difference. In the case of the GPS results, which are
referred directly to ITRF, the predicted bias and its uncertainty are derived
from Table I-3, p.II-13 of the 1991 IERS Annual Report. It reflects the slight
misalignment of the IERS EOP relative to the IERS terrestrial frame. In the
case of the SLR and VLBI results, the expected values are derived from
analyses of previous years results.

Table 3 - SYSTEMATIC DIFFERENCES OF EOP RESULTS WITH IERS
--------------------------------------------------------------------------------
Techn       Series           x (0.001")       y(0.001")       UT1(0.0001s)  Nmes
--------------------------------------------------------------------------------
 VLBI  EOP(NOAA) 92 R 01    -0.15 +- 0.08    -0.03 +- 0.09     0.00 +- 0.06  39
 VLBI  EOP(NOAA) 92 R 02                                       0.11 +- 0.05  90

 VLBI  EOP(USNO) 92 R 03    -0.43 +- 0.06    -0.12 +- 0.08     0.03 +- 0.06  27

 LLR   EOP(UTXMO)92 M 02                                      -0.91 +- 0.29  17

 SLR   EOP(CSR)  91 L 01     0.09 +- 0.07     0.17 +- 0.05     0.10 +- 0.09  48

 SLR   EOP(DUT)  91 L 02     0.98 +- 0.18    -0.84 +- 0.21                   29

 GPS   EOP(CODE) 92 P 04    -0.31 +- 0.36    -0.07 +- 0.45                  122

 GPS   EOP(CSR)  92 P 01    -0.18 +- 0.37     2.46 +- 0.48                   69

 GPS   EOP(EMR)  92 P 01    -0.44 +- 0.45     1.08 +- 0.46                   44
 GPS   EOP(EMR)  92 P 02     0.71 +- 0.39    -0.22 +- 0.46                    8

 GPS   EOP(ESOC) 92 P 01     1.01 +- 0.38     0.01 +- 0.48                  112

 GPS   EOP(GFZ)  92 P 01    -2.68 +- 0.43    -3.29 +- 0.56                   27
 GPS   EOP(GFZ)  92 P 02    +1.68 +- 0.36     1.92 +- 0.45                   68

 GPS   EOP(JPL)  92 P 01    -0.19 +- 0.38     1.51 +- 0.50                   28
 GPS   EOP(JPL)  92 P 02     0.09 +- 0.35     0.14 +- 0.45                   79
                                                         LOD : 0.16 +- 0.15  43

 GPS   EOP(SIO)  92 P 03     0.35 +- 0.35     1.68 +- 0.44                  137
--------------------------------------------------------------------------------

GPS: FORMAL AND ESTIMATED UNCERTAINTIES

The correlation of high frequency variations in the GPS polar motion results
was estimated on the basis of the residuals of each series of daily values
relative to its own smoothing (frequency cutoff: 1 cycle/10 days). The common
time intervals between two series cover 17 to 109 days. No significant
correlation was found.

Using the days which are common to pairs of series without change of reference
system, we estimate the true uncertainty of the daily EOP values by the Allan
variance (or pair variance) based on the 15 series of differences two by two
(see the 1991 IERS Annual Report, p.II-52). Table 4 shows the uncertainties
thus estimated for every GPS series, together with the  corresponding rms
formal uncertainty provided by the Processing Centre.

  Table 4 - ESTIMATED AND FORMAL UNCERTAINTY OF DAILY GPS POLAR MOTION VALUES
    ------------------------------------------------------------------------
    Techn       Series             x (0.001")           y(0.001")      Nmes
                                estim.   formal     estim.   formal
    ------------------------------------------------------------------------
     GPS   EOP(CODE) 92 P 04     0.50     0.13       0.58     0.13       66

     GPS   EOP(CSR)  92 P 01     0.59     0.20       0.69     0.20       75

     GPS   EOP(EMR)  92 P 01     0.69     0.55       0.49     0.37       66
     GPS   EOP(EMR)  92 P 02     0.48     0.23       0.39     0.20        8

     GPS   EOP(ESOC) 92 P 01     1.02     0.39       1.14     0.42       82

     GPS   EOP(GFZ)  92 P 01     1.11     0.86       1.11     0.89       26
     GPS   EOP(GFZ)  92 P 02     0.75     0.47       0.40     0.52       66

     GPS   EOP(JPL)  92 P 01     0.37     0.25       0.47     0.30       26
     GPS   EOP(JPL)  92 P 02     0.10     0.21       0.42     0.23       66

     GPS   EOP(SIO)  92 P 03     0.38     0.33       0.22     0.30       82
    ------------------------------------------------------------------------

VLBI, LLR, SLR, GPS EOP DETERMINATIONS: DAY-TO-DAY AGREEMENT WITH IERS

The series of EOP obtained by VLBI, LLR, SLR and GPS already considered in
Table 3
are considered now under the form of the weighted rms residual to
EOP(IERS) 90 C 04, after the biases of Table 2 are taken out. The statistics
are listed in Table 5.

   Table 5 - WEIGHTED RMS DIFFERENCES OF EOP RESULTS WITH EOP(IERS) 90 C 04
             The biases of Table 3 are taken out.
--------------------------------------------------------------------------------
Techn       Series           x (0.001")    y(0.001")    UT1(0.0001s)  Nmes
--------------------------------------------------------------------------------
 VLBI  EOP(NOAA) 92 R 01       0.47         0.58          0.36         39
 VLBI  EOP(NOAA) 92 R 02                                  0.48         90

 VLBI  EOP(USNO) 92 R 03       0.30         0.42          0.29         27

 LLR   EOP(UTXMO)92 M 02                                  1.18         17

 SLR   EOP(CSR)  91 L 01       0.47         0.37          0.62 (1)     48

 SLR   EOP(DUT)  91 L 02       0.90         1.08          3.41 (2)     29

 GPS   EOP(CODE) 92 P 04       0.83         0.89          0.89 (3)    132

 GPS   EOP(CSR)  92 P 01       0.90         1.57          2.73         69

 GPS   EOP(EMR)  92 P 01       1.45         0.80                       44
 GPS   EOP(EMR)  92 P 02       0.49         0.39                        8

 GPS   EOP(ESOC) 92 P 01       1.29         1.73                      112

 GPS   EOP(GFZ)  92 P 01       1.35         1.83                       27
 GPS   EOP(GFZ)  92 P 01       1.04         0.72                       76

 GPS   EOP(JPL)  92 P 01       0.72         1.31                       28
 GPS   EOP(JPL)  92 P 02       0.42         0.48                       78
                                                   LOD :  0.99         43

 GPS   EOP(SIO)  92 P 03       0.67         0.62                      137
--------------------------------------------------------------------------------
Notes : 1 - CSR  - Referred to VLBI in the long term ( p > 60 d ).
        2 - DUT  - With a drift of +0.027 ms/d and a quadratic term taken out.
        3 - CODE - With a drift of +0.045 ms/d, a quadratic term
                   and a 92d periodic term taken out.