[IGSREPORT-3] EARTH ORIENTATION Bulletin number 9 - 9 november 1992 -
IERS
IERS
Wed Nov 11 18:31:24 PST 1992
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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
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Techn Series x (0.001") y(0.001") UT1(0.0001s) Nmes
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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
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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.
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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
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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.
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