REPORT ON THE SIRGAS-CON COMBINED SOLUTION WEEK 1395 - 1465 Sonia Costa, Alberto Luis da Silva

1. REPORT ON THE SIRGAS-CON COMBINED SOLUTION WEEK 1395 - 1465 Sonia Costa, Alberto Luis da Silva Coordenação de Geodésia - CGED Instituto Brasileiro de Geografia e Estatística - IBGE Segundo Taller del Grupo de Trabajo I Montevideo, maio 26-67, 2008

2. Overview • Introduction • SIRGAS-CON sub-networks • Sub-network Maps • IGS05 Station Selection • Combination Strategy • Network Redundancy • Problems found in each sub-network solution • Outlier Rejection in the sub-networksolutions • SIRGAS-CON Sub-network Results • SIRGAS-CON Combined Solution Results • Final Considerations

3. Introduction • This combination analyses the weekly sub-network solutions provided by 3 SIRGAS Experimental Processing Centers and IGS-RNAAC-SIR: CPL : Universidad Nacional de La Plata (UNLP), Argentina; SIR: Deutsches Geodätisches Forschungsinstitut-DGFI, IGS-RNAAC-SIR, Germany; IBG: Instituto Brasileiro de Geografia e Estatística(IBGE) , Brasil; IGA: Instituto Geográfico Agustín Codazzi (IGAC), Colombia; INE: Instituto Nacional de Estadística, Geografía y Información (IEGI), México; • Analyses the results of final combination.

4. Stations from each sub-network

5. Sub-network CPL

6. Sub-network SIR

7. Sub-network IBGE

8. Sub-network IGA

9. Sub-network INE

10. All stations Total : 158

11. IGS05 Station Selection • The best datum definition for the SIRGAS-CON frame is achieved by the selection of IGS05 sites with good quality. • This selection followed the criteria: ITRF stations of high quality, good distribution over regional network, long observation history, located on rigid parts of tectonic plates. • Problems: • Stations KOUR, BOGT and AREQ present only in ITRF2005 solution • Stations JAMA and RIOG are out of operation • Stations VESL and ASC1 show up only in one sub-network • Station GLPS is located in a region of high tectonic activity

12. IGS05 Station Selection • Eleven stations: BRAZ, CHPI, CONZ, CRO1, LPGS, MANA, MDO1, OHI2, SANT, SCUB and UNSA • Coordinates IGS05 propagated to 2007.4 :

13. IGS Fiducial Sites

14. Combination Strategy • The unconstrained solution, implementing a minimum constraints approach through three translations conditions, preserves the original characteristics of the network and at the same time provides the alignment to ITRF; • The combination strategy is divided into two main parts. The first part produces the unconstrained weekly combination from each sub-network (center) and the second produces the unconstrained final combination from the results of the first part (sub-network results).

15. A priori Coordinate File (propagated to 2007.4)‏ Sub-Network Combination Scheme CPLwwww7.SNX IGS05_R.CRD IGS05_R.VEL IGAwwww7.SNX SIRwwww7.SNX IBGwwww7.SNX 3-Parameter Helmert Transformation Iteration Outlier Rejection Criteria 15/15/30 mm NEU Final Combination - all Processing Centers' Solutions

16. SIRGAS-CON Combination Strategy The following steps describe the combination strategy: • Each sub-network solution is aligned to a subset of fiducial stations from the IGS05 solution of epoch 2007.4 by No Net Translation (NNT) conditions. It means that each resulting combined solution is expressed in IGS05 at the central epoch of the sub-network solution. • Each sub-network solution's covariance matrix is scaled by the weighted root mean square (WRMS) of the residuals from the transformation in step 1. • Residuals are tested for outliers which are removed from each sub-network solution and steps 1-2 are repeated again in each sub-network. This iterative process is to refine the estimation of variance factor. The threshold limits for coordinate repeatability residuals are 15 mm for east and north components and 30 mm for up component. • Compare each sub-network combined solutions with IGS05 in order to see network effects through transformation parameters; • All sub-network solutions are combined together to give a final combination solution. The final combined solution is re-aligned to a subset of fiducial stations from the IGS05 solution of epoch 2007.4 by No Net Translation (NNT) conditions. • The covariance matrix of the combined solution is scaled by the WRMS of residuals from the transformation in step 3. • Residuals are tested for outliers which are removed from the regional solutions and steps 6-7 are repeated until no outliers remain in the combined solution.

17. NetworkRedundancy

19. Problems found in each sub-network solution • CPL: Week solutions 1395 and 1457- a priori constraints matrix block incomplete in SINEX – matrix had to be regularized. • Problems related with station receiver/antenna and antenna height • Wrong domes number • Stations EXU0, GRE0, GTK0, MIA3, NAS0 and SMRT with inadequate domes number

20. Outlier Rejection in the sub-networksolutions • Exclusion in some solutions : CRAT, BELE, NAUS, MANA, OHI2, JAMA, MZAS and PUR3. • In all solutions: GLPS (+2 to -5 cm in E), CONZ(1 to 2 cm in E), BDOS (-1.7 to 1.7 cm in E), BOGA (-5 to 3 cm in U), LPAZ (3 to -3 cm in E)

21. SIRGAS-CON Sub-network Results Mean and Standard deviation of transformation parameters between weekly solutions of each sub-network to combined sub-network solution.

22. SIRGAS-CON Sub-network ResultsRMS of transformation between weekly solution of each sub-network to the combined solution of each processing center.

23. SIRGAS-CON Sub-network Results Scale estimated in the weekly solution of each processing center

24. SIRGAS-CON Sub-network Results Transformation parameters between IGS05(epoch 2007,4) and each sub-network combination.

25. SIRGAS-CON Combined Solution Results • Alignment method: Minimal constraint conditions on fiducial stations by No Net Translation (NNT) conditions • Reference Frame: IGS05 • Reference epoch (the middle of the time interval):2007-06-06, 00:00:00(2007.4) • Fiducial stations: BRAZ, CHPI, CONZ, CRO1, LPGS, MANA, MDO1, OHI2, SANT, SCUB and UNSA

26. SIRGAS-CON Combined Solution ResultsCLP Residuals of station repeatability obtained in the final solution

27. SIRGAS-CON Combined Solution ResultsSIR Residuals of station repeatability obtained in the final solution

28. SIRGAS-CON Combined Solution ResultsIBG Residuals of station repeatability obtained in the final solution

29. SIRGAS-CON Combined Solution ResultsIGA Residuals of station repeatability obtained in the final solution

30. SIRGAS-CON Combined Solution Results Higher RMS of residuals of station repeatability in the final combination

31. SIRGAS-CON Combined Solution Results Transformation parameters between sub-network solutions to the final combination

32. SIRGAS-CON Combined Solution Results Transformation parameters between IGS05 (epoch 2007,4) and the final combination

33. Final Considerations • A total of 156 stations were available for the final solution of four processing centers. The results were satisfactory even considering the problems related to antenna/receiver identifications as well as related to antenna height. • Some organization needs to be done for all processing centers to use the same identification for receiver/antenna as well as antenna height. It’s suggested to make available a station information file and Ocean loading file. File updates are in the responsibility of the network coordinator. Radome codes need to be supplied. • More IGS stations should be included in the solutions of processing centers, this is the case of IBGE, in order to have the redundancy of five or more IGS stations in different sub-networks. • Add more redundant solutions for as many stations as possible, especially those in the SIRGAS-CON network. Some stations are only in one regional solution and therefore have no independent quality control checks.