REPORT ON THE SIRGAS-CON COMBINED SOLUTION WEEK 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

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-network solutions SIRGAS-CON Sub-network Results SIRGAS-CON Combined Solution Results Final Considerations

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.

Stations from each sub-network CenterCountryIGS Reference stationsIGS stations CPLBrasil, Uruguay, Argentina, Chile Guianas GLPS, BRAZ, UNSA, SANT, CONZ, LPGS, CHPI, OHI2, MANA, SCUB, CRO1 GUAT, SSIA, JAMA, BOGT, RIOP, AREQ, COPO, CFAG, ANTC, PARC, RIO2, KOUR, BRFT SIRArgentina, Brasil, Uruguay, Chile, Equador, Colombia, Venezuela, Guianas, Mexico, Central America and Caribbean region GLPS, BRAZ, UNSA, SANT, CONZ, LPGS, CHPI, OHI2, GOLD, PIE1, MDO1, MANA, SCU1, CRO1, ASC1,VESL ELEN, GUAT, SSIA, INEG, CIC1, BRMU, BDOS, RIOP, KOUR, BRFT, AREQ, GOUG IBGBrazil, Uruguay, Argentina, Chile, Equador, Venezuela and Guianas GLPS, BRAZ, UNSA, SANT, CONZ, LPGS, CHPI, OHI2 AREQ, RIOP, KOUR, BRFT, BOGT, COPO, CFAG, ANTC, RIO2, PARC IGAColombia, Mexico, Central America and Caribbean region GLPS, BRAZ, UNSA, CHPI, CRO1, SCUB, MANA, MDO1, PIE1, GOLD ELEN, GUAT, SSIA, INEG, CIC1, BRMU, BDOS, RIOP, KOUR, BRFT, AREQ INEMexico, U.S. and Caribbean region MANA, SCUB, PIE1, MDO1 GUAT, INEG, PUR3, BRMU, CIC1

Sub-network CPL

Sub-network SIR

Sub-network IBGE

Sub-network IGA

Sub-network INE

All stations Total : 158

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

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

IGS Fiducial Sites

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).

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

The following steps describe the combination strategy: 1.Each sub-network solution is aligned to a subset of fiducial stations from the IGS05 solution of epoch 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. 2.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. 3.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. 4.Compare each sub-network combined solutions with IGS05 in order to see network effects through transformation parameters; 5.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 by No Net Translation (NNT) conditions. 6.The covariance matrix of the combined solution is scaled by the WRMS of residuals from the transformation in step 3. 7.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. SIRGAS-CON Combination Strategy

Network Redundancy

Sub- networ k n° of stations Scale Factor CPL DGF IBG IGA INE

Problems found in each sub-network solution CPL: Week solutions 1395 and 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

Outlier Rejection in the sub-network solutions 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)

SIRGAS-CON Sub-network Results SOL RMS(m)TX(m)TY(m)TZ(m) ROT_X (") ROT_Y (") ROT_Z (") SCL (ppm) CPLMEAN0,004580,0003-0,0009-0, ,00002 STDDEV0,000740,00560,00470,00840,0003 0,00020,00052 SIRMEAN0,005250,0003-0,0009-0, ,00002 STDDEV0,001470,00560,00470,00840,0003 0,00020,00052 IBGMEAN0,004250,0003-0,0009-0, ,00002 STDDEV0,000740,00560,00470,00840,0003 0,00020,00052 IGAMEAN0,004710,0003-0,0009-0, ,00002 STDDEV0,001380,00560,00470,00840,0003 0,00020,00052 Mean and Standard deviation of transformation parameters between weekly solutions of each sub-network to combined sub-network solution.

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

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

SIRGAS-CON Sub-network Results Transformation parameters between IGS05(epoch 2007,4) and each sub-network combination. SOL.RMS (mm) TX (mm) /  ± TY (mm) /  ± TZ (mm) /  ± ROT_X /  ± (") ROT_Y /  ± (") ROT_Z /  ± (") SCL /  ± (ppm) CPL / / / / / / / SIR / / / / / / / IBG / / / / / / / IGA / / / / / / /

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): , 00:00:00(2007.4) Fiducial stations: BRAZ, CHPI, CONZ, CRO1, LPGS, MANA, MDO1, OHI2, SANT, SCUB and UNSA

SIRGAS-CON Combined Solution Results CLP Residuals of station repeatability obtained in the final solution

SIRGAS-CON Combined Solution Results SIR Residuals of station repeatability obtained in the final solution

SIRGAS-CON Combined Solution Results IBG Residuals of station repeatability obtained in the final solution

SIRGAS-CON Combined Solution Results IGA Residuals of station repeatability obtained in the final solution

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

SIRGAS-CON Combined Solution Results SOL. RMS (m)TX(m)TY(m)TZ(m) ROT_X (") ROT_Y (") ROT_Z (")SCL(ppm) CPL0, ,00090,00040, ,00001 SIR0,00230,0011-0,0023-0,00050,0000 0,00005 IBG0,0015-0,0015-0,0014-0,00610,0001 0,0000-0,00043 IGA0,00130,0006-0,0024-0,00060,00010, ,00017 MEAN0,00140,0002-0,0018-0,00170,00010, ,0001  0,00070,00110,00070,00300,0001 0,00000,0002 Transformation parameters between sub-network solutions to the final combination

SIRGAS-CON Combined Solution Results Transformation parameters between IGS05 (epoch 2007,4) and the final combination RMS (mm) TX (mm) /  ± TY (mm) /  ± TZ (mm) /  ± ROT_X /  ± (") ROT_Y /  ± (") ROT_Z /  ± (") SCL /  ± (ppm) / / / / / / /0.0003

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.