The IGS contribution to ITRF2013–

Preliminary results from the IGS repro2SINEX combinations

Paul Rebischung, Bruno Garayt, Xavier Collilieux, Zuheir Altamimi

AGU Fall Meeting 2014, Abstract G11C-07, San Francisco, 15 December 2014 1

The IGS 2nd reprocessing (repro2)

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• Re-analysis of GNSS data collected by the IGS network since 1994 using the latest models and methodology– Reduce systematic errors in IGS products– Provide IGS contribution to ITRF2013

• Main updates since repro1:– Daily data integrations (instead of weekly) – GLONASS data processed by some ACs– IGb08/igs08.atx framework– IERS2010 Conventions– New yaw attitude models for eclipsing satellites– A priori modeling of Earth radiation pressure and antenna thrust– See details at: http://acc.igs.org/reprocess2.html

Analysis Center submissions

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Contributions from 7 operational ACs

+ 2 TIGA contributions

• Submitted products include:– Satellite orbits and clocks– Terrestrial frames and EOPs (daily SINEX files)

1st combinations (1/2)

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WRMS of station position residuals(i.e., of daily « AC – combined » differences)

– Outlying days for several ACs: ongoing re-submissions

1st combinations (2/2)

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Smoothed WRMS• ULR:

– Large systematic errors in East– Issue in sub-network combos– Ongoing re-submissions

• GRG:– Large systematic errors in Up– Pronounced semi-annual

variations in North and Up– Under investigation

→ 2nd combinations with GRG, ULR & GTZ included for comparison only

• MIT seems to dominate in Up (and North).– Because « classical » WRMS

are biased in favor of ACs with non-common stations.

→ Use Sillard (1999)’s unbiased WRMS

2nd combinations (1/2)

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Smoothed WRMSSmoothed, unbiased WRMS

# stations in AC solutions

• GFZ’s North WRMS vs. mean ionosphere TEC:

– Error in 2nd order ionospheric corrections

– New products submitted, but still affected by several issues

→ 3rd combinations with GFZ included for comparison only

2nd combinations (2/2)

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Smoothed, unbiased WRMS

― GFZ’s North WRMS― a + (b x mean_TEC)

3rd combinations

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Smoothed, unbiased WRMS• Inter-AC agreement

after 2004:– Horizontal: ≈ 1 – 1.5 mm– Vertical: ≈ 3 – 4 mm– Comparable to the weekly

repro1 results

• Substantial degradation before 2000 (and 1997)– Much less marked in repro1:

3D RMSof repro1

combination residuals

Spectral analysisStacked periodograms of station position residuals

(computed using stations with > 3000 days of data)

East North

Up

• Background: flicker + white noise• Spectral peaks at:

– Annual period; GPS draconitic harmonics– Fortnightly periods (14.8, 14.2, 13.7 & 13.2 d)

– 9.1 d (MIT); 8.2 & 7.8 d (COD, ESA, MIT);7.0 d (MIT); 3.65 & 2.2 d (GRG)

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Scale

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AC / ig2 scale offsets

AC

Offset

(mm)

Rate (mm/yr)

WRMS

(mm)

cod

0.2 -0.02 0.4

emr

-0.5 -0.01 0.5

esa

0.4 0.05 0.5

jpl

-0.2 0.00 0.5

mit

-0.1 -0.01 0.3

• Inter-AC agreement: 0.3 – 0.5 mm– Scale rate differences < 0.1 mm/yr

• Combined scale rate wrt IGb08:-0.03 mm/yr– Contribution to ITRF2013 scale rate?

ig2 / IGb08 scale offsets

Origin: Y component

AC / ig2 Y origin offsets

AC

Offset

(mm)

Rate (mm/yr)

WRMS

(mm)

cod

-2.6 0.15 3.3

emr

1.8 -0.25 5.4

esa

0.2 -0.32 3.1

jpl

-3.3 -0.08 4.6

mit

1.3 0.08 2.1

― ig2 / IGb08 Y origin offsets― SLR / ITRF2008 Y origin offsets (cf. G11C-08)

• Inter-AC agreement: ≈ 3 – 5 mm– nearly 10 times larger than for scale

• Y component of combined origin:– Good agreement in phase with SLR– Annual amplitude slightly over-estimated

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Origin: X component

AC / ig2 X origin offsets

AC

Offset

(mm)

Rate (mm/yr)

WRMS

(mm)

cod

-1.4 0.14 3.2

emr

0.2 0.12 4.6

esa

-0.8 0.22 2.9

jpl

2.3 0.10 4.4

mit

0.4 -0.14 1.9

― ig2 / IGb08 X origin offsets― SLR / ITRF2008 X origin offsets (cf. G11C-08)

• Inter-AC agreement: ≈ 3 – 5 mm– nearly 10 times larger than for scale

• X component of combined origin:– Annual amplitude under-estimated– Broad spectral peak around 3.12 cpy

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Origin: Z component

AC / ig2 Z origin offsets

AC

Offset

(mm)

Rate (mm/yr)

WRMS

(mm)

cod

0.9 0.05 8.9

emr

2.1 -0.16 8.6

esa

-1.6 0.15 6.5

jpl

-1.8 0.04 8.0

mit

0.2 -0.07 3.7

― ig2 / IGb08 Z origin offsets― SLR / ITRF2008 Z origin offsets (cf. G11C-08)

• Inter-AC agreement: ≈ 6 – 9 mm– nearly 20 times larger than for scale

• Z component of combined origin:– Spoiled by GPS draconitic harmonics– Annual signal out-of-phase with SLR

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Earth Orientation Parameters

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AC / ig2 X-pole differences AC / ig2 Y-pole differences

AC / ig2 X-pole rate differences AC / ig2 Y-pole rate differences

AC / ig2 LOD differences

AC XPO

μas

YPO

μas

XPORμas/d

YPORμas/d

LOD

μs/d

cod

34.7

33.5

175.3

184.1

17.1

emr

40.0

44.4

218.1

182.9

35.2

esa

25.6

25.8

138.6

143.5

15.8

jpl 31.0

28.0

169.2

172.4

27.0

mit

16.9

16.4

62.7

70.1

15.5

WRMS of EOP residual time series

• Inter-AC agreement: ≈ 30 μas; 150-200 μas/d; 15-30 μs/d

Summary

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• Station positions:– Post-2004 inter-AC agreement comparable to weekly repro1 results– Substantially worse in early years

• Scale:– Excellent inter-AC agreement– Contribution to ITRF2013 scale rate?

• Origin:– No substantial improvement

• EOPs:– Inter-AC agreement slightly improved compared to repro1

Next steps

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• Expected by end of January 2015:– Re-submissions (COD, GFZ)– Extensions to 2014 (COD, ESA, MIT)

• Final combined solutions due by end of February 2015

• If time allows, study stationresidual time series:

• Form long-termcumulative solution– Revised discontinuity list– Modeling of post-seismic

deformations

ULAB North residuals

Thanks for your attention!

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Pole coordinates

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AC / ig2 X-pole differences AC / ig2 Y-pole differences

Pole rates

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AC / ig2 X-pole rate differences AC / ig2 Y-pole rate differences

Length of day

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AC / ig2 LOD differences Normalized periodograms

Origin: X component

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AC / ig2 X origin offsets Normalized periodograms

Origin: Y component

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AC / ig2 Y origin offsets Normalized periodograms

Origin: Z component

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AC / ig2 Z origin offsets Normalized periodograms

Annual – East

cod emr esa

gfz grg jpl

mit gtz ulr

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Annual – North

cod emr esa

gfz grg jpl

mit gtz ulr

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Annual – Up

cod emr esa

gfz grg jpl

mit gtz ulr

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Relative formal errors: pole coordinates

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σXPO / median(σsta) [mas/mm] σYPO / median(σsta) [mas/mm]

Relative formal errors: pole rates & LOD

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σXPOR / median(σsta) [mas/d/mm] σYPOR / median(σsta) [mas/d/mm]

σLOD / median(σsta) [ms/d/mm]

Relative formal errors: geocenter

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σXGC / median(σsta) [mm/mm] σYGC / median(σsta) [mm/mm]

σZGC / median(σsta) [mm/mm]