Instituto Brasileiro de Geografia e Estatística

About the publication - Processing Center

The establishment and materialization of a geodetic referential for the Americas is one of the major activities of SIRGAS. The materialization is made through the establishment of a geodetic network of reference, being an activity of the Workgroup I - WGI. Aiming at this purpose, two GPS measurement campaigns were carried out in 1995 and 2000, which established the SIRGAS95 and SIRGAS2000 networks, respectively.

Taking into account the increasing number of GNSS permanent stations established in the American continent over the last years, the WGI decided to create the Continuous Reference Network - SIRGAS-CON, which comprises the GNSS permanent stations of the networks of the Latin American and Caribbean countries. The organization of the SIRGAS-CON Network was proposed and accepted in the May 2008 meeting of the WGI, involving the following components: Local Operational Centers or data centers, Local Processing Centers, Combination Centers and the Coordinator of the network. Most of those components already existed, though there was a need to coordinate a number of activities and the responsibility of each part. Another need was the subdivision of the network into sub-networks in order to process the stations by more than one center, allowing a redundancy in the solutions and a better analysis of the results.

Currently – July 2014 –, the SIRGAS-CON network comprises nearly 300 stations located in Latin America, Caribbean islands and Antarctica, distributed along:

I - A network with continental coverage (SIRGAS-C), characterizing a densification of the ITRF in Latin America and weekly processed by the DGFI, as an IGS-RNAAC-SIR (IGS Regional Network Associate Analysis Center) analysis center.

II - National networks of reference (SIRGAS-N), which densify the continental network and are calculated by the SIRGAS Local Processing Centers, such as:

• a) CEPGE (Ecuador)
• b) CNPDG-UNA (Costa Rica)
• c) CPAGS-LUZ (Venezuela)
• d) IBGE (Brazil)
• e) IGAC (Colombia)
• f) IGM-Cl (Chile)
• h) IGN-Ar (Argentina)
• i) INEGI (Mexico)
• j) SGM-Uy (Uruguay)

Both the continental and national networks have the same quality features and each station is processed by three processing centers. These Centers produce loosely-constrained weekly solutions of the SIRGAS-N networks, which are later coupled with the SIRGAS-C continental network, thus establishing the position and speed of every station. This task is carried out by the IBGE and DGFI and the results are released to the community through the ftp.sirgas.org server. The "fixed" weekly solutions are related to the time of the observation and ITRF in force, now the IGb08, an accomplishment of the ITRF2008.

Processed Stations

The stations belonging to the SIRGAS-CON network have double-frequency equipment and are materialized by means of stable structures installed on the top, called forced centering devices.

More information on the configuration of a SIRGAS-CON station can be found in the Installation Guide of SIRGAS-CON Stations.

Information on each station can be found on: ftp://ftp.sirgas.org/pub/gps/DGF/station/log

Results

The SIRGAS - IBGE Processing Center produces weekly files in the SINEX format (Software Independent Exchange), of the sub-network processed by the IBGE. Currently about 120 stations belonging to the SIRGAS-CON network located in Argentina, Bolivia, Brazil, French Guiana, Peru, Suriname and Uruguay are included in this processing.

The results files here available are injunction free and can be used to adjust differential solutions, in the densification of any area. These files are available three weeks after the tracking date of the observation. The following denomination is adopted for SINEX files:

IBGwwww7.SNX ? Injunction-free solution
(where wwww = GPS week)

The results files are available on: http://geoftp.ibge.gov.br/informacoes_sobre_posicionamento_geodesico/sirgas/processamento/

The strategies, parameters and models adopted to produce the weekly results are: