PDF file - Laboratoire de Géologie de l'Ecole normale supérieure - Ens

X - 4 SIMONS ET AL.: GPS MEASUREMENTS IN S.E. ASIA TO REFINE SUNDALAND MOTION
Table 2. Daily Coordinate Repeatabilities 1994-2003. The tables
shows the number of sites observed yearly in each region,
along with the number of daily solutions used (and the number
of outliers) in the multi-day averaging, followed by the RMS of
the residuals w.r.t. each multi-day averaged solution. Regions
marked with *, indicate that permanent data was daily processed
in those years.
Year Description Sites Daily RMS Residuals (mm)
Observed Solutions North East Up
1994 GEODYSSEA 39 189 (- 15) 2.4 5.5 11.7
Region 1 5 19 (- 2) 2.8 3.4 13.7
IGS 21 274 (- 18) 3.1 5.7 11.1
1996 GEODYSSEA 40 224 (- 14) 2.2 5.7 13.3
Region 1 3 15 (- 0) 2.7 6.5 18.9
Region 3 7 27 (- 1) 2.9 6.6 11.2
IGS 25 325 (- 16) 3.1 6.8 11.5
1997 GEODYSSEA 14 96 (- 5) 2.1 4.3 9.5
Region 3 10 55 (- 2) 2.1 3.5 9.1
IGS 27 352 (- 7) 2.5 4.0 9.0
1998 GEODYSSEA 38 186 (- 4) 1.7 3.5 8.6
Region 1* 10 1036 (- 2) 1.9 2.8 8.1
Region 2 9 54 (- 10) 1.5 3.8 8.1
Region 3 10 56 (- 4) 1.9 5.0 8.7
IGS* 30 7630 (- 78) 2.4 4.0 8.9
1999 GEODYSSEA 4 20 (- 2) 2.2 5.2 9.1
Region 1* 5 1204 (- 8) 1.7 2.8 7.9
Region 2* 15 3189 (- 11) 2.0 3.0 8.8
Region 3* 11 183 (- 16) 2.4 5.7 10.1
IGS* 31 9092 (-141) 2.5 4.6 9.7
2000 GEODYSSEA 10 44 (- 2) 1.9 3.5 9.5
Region 1* 10 782 (- 13) 2.1 4.4 8.5
Region 2* 15 4419 (- 30) 2.1 4.0 8.9
Region 3* 18 592 (- 22) 2.2 7.1 9.9
IGS* 30 9718 (-240) 2.6 5.3 10.3
2001 GEODYSSEA 4 19 (- 0) 2.0 4.3 12.7
Region 1* 10 500 (- 9) 1.9 3.8 9.0
Region 2* 17 5438 (- 33) 1.9 3.9 9.5
Region 3* 16 1243 (- 27) 1.8 4.1 9.5
IGS* 30 9287 (-142) 2.3 4.5 9.2
2002 GEODYSSEA 9 57 (- 6) 2.6 3.3 8.0
Region 1 5 68 (- 0) 2.4 3.8 9.8
Region 2 17 412 (- 12) 2.5 4.1 10.8
Region 3 25 433 (- 6) 2.0 3.4 8.7
IGS 29 1514 (- 20) 2.2 3.7 7.6
2003 GEODYSSEA 6 20 (- 1) 2.5 2.7 7.7
Region 2 14 200 (- 1) 1.7 3.4 8.1
Region 3 24 272 (- 11) 1.8 3.4 8.6
IGS 28 1033 (- 3) 1.7 2.5 6.3
Because consistency among the phase corrections is an important
issue and NGS provides more regularly updates when new GPS antennae
become available, preference to the NGS calibration tables
was given in this analysis. It is possible to directly map the daily
PPP coordinate solution(s) into (at present) the ITRF-2000, using
Helmert transformation parameters from JPL which are compatible
with the JPL precise orbits and satellite clocks. Although this
approach works well, the parameters sometimes are not directly
available, and they need to re-computed at JPL each time a new
ITRF solution becomes available.
In a final step, the solutions of each station can be simply merged
into one daily covariance band matrix (no correlations between different
stations) for the complete network, after which the ambiguities
can be resolved. This is the only stage at which GIPSY relies
on double-differences from the ionosphere-free combined GPS
phase and pseudorange measurements. Current software memory
requirements prevent that ambiguities can all be solved in one step
for big networks. Therefore the ambiguities are resolved in successive
iterations, where the shortest baselines are solved for first
(boot-strapping), using a sequential wide- and narrow-laning approach
to fix the phase biases to the correct integers. This works for
both short (< few 100 km, most ambiguities fixed) and long baselines
(up to 8000 km, few ambiguities fixed). When the iterations
are completed, the daily covariance matrix is updated, and has now
become a full matrix, due to the correlations introduced in the ambiguity
fixing procedure. Throughout the following computations of
multi-day averaged coordinate solutions, their transformation into
the ITRF, and the final velocity estimation, full covariance matrices
can be used.
3.1. Multi-day averaged solutions
The daily PPP coordinate solutions were combined into weekly
or campaign averaged coordinate solutions whereby any systematic
differences between the various daily network solutions are
eliminated by computing optimized 7-parameter Helmert transformations
using a least squares adjustment. In this process, any daily
station solutions identified as outliers are downweighted (all components,
or only the vertical component). The (default) criteria used
to detect these outliers can be automatically scaled up, if the daily
positions for a given site exhibit a lot of noise. This is done to
prevent almost all solutions for a given site to become marked as
outliers. The above procedure only removes extreme outliers from
Table 3. Residuals IGS sites after ITRF-2000 transformations.
Year IGS sites RMS Residuals (mm)
used North East Up
1994 15 1.7 2.3 8.8
1996 20 2.7 3.1 9.2
1997 20 1.8 2.5 6.4
1998 19-23 2.3 2.7 7.2
1999 15-22 2.2 2.9 8.3
2000 15-21 2.2 3.1 8.6
2001 13-19 2.0 2.9 8.2
2002 15-17 2.0 2.4 7.7
2003 13-14 2.2 1.7 8.2
Table 4. Residuals stations w.r.t. linear trend fitting. Shown
first are the number of velocity estimates obtained for each S.E.
Asia and IGS (sub)network, along with the number of multi-day
averaged solutions used (and rejected) in the velocity estimation.
The last 3 columns give the RMS of the residuals between the
multi-day averaged position components in ITRF-2000 and the
fitted linear trend for each site. These values are not available
for the ENS site as they were only measured twice.
RMS Residuals (mm)
Description Sites Solutions North East Up
GEODYSSEA 38 141 (- 17) 2.9 3.3 8.3
Region 1
THAICA 5 16 (- 2) 2.6 4.9 3.9
ENS 4 8 (- 0) N/A N/A N/A
GAME-T 6 518 (- 7) 2.5 3.3 9.3
Region 2
MASS 17 2063 (- 28) 2.3 3.2 8.0
Region 3
GEODYSSEA Sec. 14 54 (- 10) 2.6 2.5 7.7
BAKO monuments 6 24 (- 4) 4.0 2.6 7.4
BAKO permanent 7 319 (- 8) 2.5 3.8 9.1
IGS
Local 3 456 (- 28) 3.3 3.6 10.3
Regional+global 29 4922 (- 98) 2.0 3.0 7.5
Total 129 8521 (-202) 2.3 3.1 8.0