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The ILRS contribution to the development of ITRF2013
19th International Workshop on Laser Ranging, 27-31 October 2014, Annapolis
G. Bianco Agenzia Spaziale Italiana, CGS - Matera
V. Luceri, B. Pace e-GEOS S.p.A., ASI/CGS
E. Pavlis, D. König, M. Kuzmicz-Cieslak GEST/UMBC - Baltimore
ASI GRGS
GFZ DGFI ESA
NSGF
JCET
The ILRS Analysis&Combination Centers
BKG
Primary CC Backup CC
The ILRS processing flow • The official ILRS analysis centers (ACs) produce daily and
weekly solutions that are combined by the two combination centers (CCs)
• Solutions contain SSC and daily EOP, using Lageos and Etalon data, according to the ILRS/AWG guidelines
• Same processing strategy has been adopted for the ITRF2013 solutions
ASI/CGS ILRSA Primary
JCET ILRSB Backup
ILRS ACs Database ILRS CCs
CDDIS EDC
CDDIS EDC
Database
JCET
BKG
DGFI
GFZ
ASI
ESA
GRGS
NSGF
The final combined product quality is affected by different factors, such as:
data analysis • Conventions adopted • Application/estimation of system biases • Satellite Center of Mass correction • Data coverage • SW • Hidden constraints
combination • Balance in the contribution of all the ACs solutions • Outlier editing, which affects the iterative computation of the solution
scaling factors in the combination process
The quality of the final product
Input SLR data
ILRSA solution basic facts
Ø Coverage: 1983-2013, Lageos and Etalon data
Ø 8 ACs have submitted several versions of their SLR SSC/EOP 7-day arc solutions covering the period 1993 – 2013 during April-September 2014
Ø The combined ILRSA has been issued in its final version on October 10th
Ø 7 ACs have submitted their 15-day arc time series covering the period 1983 – 1992 , the last one was submitted a few days ago
Ø The final time series for 1983-1992 was delivered on October 24th
The ASI-CGS combination procedure is based on the direct combination of loose constrained solutions (“Methodology for global geodetic time series estimation: A new tool for geodynamics”, Davies and Blewitt, 2000).
Translations Rotations Scale
The ILRSA combination approach
Translations Rotations Scale
The combination is performed along the lines of the iterative Weighted Least Square technique: each contributing solution plays the role of a ‘pseudo-observation’ whose residuals with respect to the combined solution must be minimized; each solution is stacked using its full covariance matrix rescaled by a factor to reach convergence and to balance the contributions; for each combination step proper editing criteria are applied
Looseness of the SLR solutions
∼5 mas
∼5 mas
∼10 mas
∼10 mas
∼10 mas
∼15 mas
Looseness of the SLR solutions
∼0.5 mm
∼0.5 mm
∼1 mm
∼1.5 mm
∼1.5 mm
∼5 mm
∼0.5 mm ∼1.5 mm
ILRSA solution overall quality
∼5 mm
∼11 mm
wrms of SSC residuals wrt SLRF2008 – core sites
Intra-technique consistency
wrms of SSC residuals wrt ILRSA – all sites
Origin with respect to SLRF2008
1995 2000 2005 2010 2015-30
-20
-100
10
2030
mm
ILRS TZ
Linear Rate: (0.284 ± 0.025) mm/yr Residual w rms= 6.532 mm1995 2000 2005 2010 2015
-30
-20
-10
0
10
2030
mm
ILRSA TY
Linear Rate: (-0.120 ± 0.010) mm/yr Residual w rms= 3.421 mm1995 2000 2005 2010 2015
-30
-20-10
0
102030
mm
ILRS TX
Linear Rate: (-0.007 ± 0.011) mm/yr Residual w rms= 3.710 mm
Rate = -0.01 ± 0.01 mm/yr
Rate = -0.12 ± 0.01 mm/yr
Rate = 0.28 ± 0.03 mm/yr
Tx
Ty
Tz
Scale with respect to SLRF2008
Rate = -0.371 ± 0.001 mm/yr Scale
EOP vs USNO: arc weighted mean µ
as
µas
µ
s
X-Pole
Y-Pole
LOD
Remarks
q The ILRS contribution to ITRF2013 followed updated guidelines for both ACs and CCs (conventions adopted, application/estimation of system biases, data editing, treatment of hidden constraints);
q The analysis of the data span 1983-2013 for the final official ILRS combined solution, ILRSA v60, has been delivered on October 24th
q The ILRS time series shows: Ø overall coherence of all the final AC contributing solutions Ø 5mm WRMS of the Core Site residual w.r.t. SLRF2008 Ø Very neat Helmert parameter time series, allowing to detect
small secular and periodic components. Tz is noisier, as expected
Ø A signature in the Ty and scale is visible in 2010 and needs deeper investigation
Acknowledgement
Credit is due to
• the ILRS Analysis Centers for their big effort in reprocessing the 30 year long data set
• the ILRS Data Centers for their prompt response to all our requests