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