The project for the establishment of a South American Geocentric Reference System (Sistema de Referencia Geocéntrico para América del Sur, SIRGAS) was initiated in October 1993 during an international conference held in Asunción, Paraguay, and organized by the International Association of Geodesy (IAG), the Panamerican Institute of Geodesy and History (PAIGH), and the U.S. Defence Mapping Agency (DMA). The objectives of the project defined at this meeting were
A total of 58 sites on the South American mainland and the surrounding areas were selected to form the SIRGAS reference frame. All these sites were observed simultaneously during a continuous GPS campaign from May 26, 1995, 0:00 UT to June 4, 1995, 24:00 UT. The observation data files were collected and are available at two data centers at Deutsches Geodaetisches Forschungsinstitut (DGFI), Munich, Germany and Instituto Brasileiro de Geografia e Estatística (IBGE), Rio de Janeiro, Brazil.
The data processing was done by two processing centers at DGFI and the National Imagery and Mapping Agency (NIMA, formerly DMA), St. Louis, MO/USA using different softwares (Bernese at DGFI and GIPSY at NIMA). The two independent results were combined and transformed to the ITRF 94 by means of nine identical stations of the International GPS Service (IGS). The precision of station coordinates is in the sub-centimeter level.
All the processing procedure was discussed during project meetings at Santiago, Chile, August 1996 and Isla Margarita, Venezuela, April 1997. At the latter meeting the final station coordinate solution was adopted as the official SIRGAS reference frame and recommended to be used by all South American countries as the basis for the national reference frames.
Realization of the Geocentric Datum
The South American countries started to refer their national reference networks to the SIRGAS frame immediately after its realization. In most cases completely new GPS networks were installed including some identical stations with the existing classical triangulation networks. By this means, a transformation from the old datums (e.g. the Provisional South American Datum 1956, PSAD 56, or the South American Datum 1969, SAD 69) to the new SIRGAS datum is feasible.
At present, in nearly all South American countries a national GPS network within the SIRGAS frame has been installed. Thereby a dense station distribution covering the total continent with a unique datum for its coordinates is established. The typical spacing between stations is 100 km. A further densification (second order networks) has started in several countries.
Vertical Reference System
During the IAG Scientific Assembly in Rio de Janeiro 1997, the SIRGAS Working Group III "Vertical Datum" was created. The objective of this WG is to define and to establish a unique vertical datum for the existing and future height systems in all South American countries.
The WG III met for a Workshop in Santiago, Chile, in August 1998 and released the main resolutions
The activities of the SIRGAS Working Groups will continue during the next years. In order to monitor the coordinate changes of the SIRGAS reference frame (station velocities) its striven for permanent GPS observations in most of the stations. Presently, about 20 sites are included in the IGS regional network weekly processed by the Regional Network Associate Analysis Center for SIRGAS (RNAAC-SIR) at Deutsches Geodaetisches Forschungsinstitut (DGFI), Munich. A repetitive GPS campaign shall be planned for those stations not included in the RNAAC network.
Costa, SMA., K.D. Pereira, D. Beattie: The integration of Brazilian geodetic network into SIRGAS. IAG Symposia, No. 118, 187-192, Springer 1998.
Drewes, H., L.P. Fortes, M.J. Hoyer, R. Barriga: Status report of the SIRGAS project. IGS 1996 Annual Report, 433-436, 1997.
Drewes, H.: Time evolution of the SIRGAS reference frame. Springer, IAG Symposia, No. 118, 174-179, Springer 1998.
Drewes, H., H. Tremel, J.N. Hernandez: Adjustment of the new Venezuelan national GPS network within the SIRGAS reference frame. Springer, IAG Symposia, No. 118, 193-198, Springer 1998.
Fortes, L.P., M.J. Hoyer, W.H. Subiza, H. Drewes: The SIRGAS project. IGS Annual Report 1994, 247-250, 1995.
Hoyer, M., S. Arciniegas, K. Pereira, H. Fagard, R. Maturana, R. Torchetti, H. Drewes, M. Kumar, G. Seeber: The definition and realization of the reference system in the SIRGAS project. Springer, IAG Symposia, No. 118, 167-173, Springer 1998.
Kaniuth, K., H. Drewes, K. Stuber, H. Tremel, J. Moirano: Results of the SIRGAS 95 GPS network processing at DGFI/I. Springer, IAG Symposia, No. 118, 180-186, 1998.
Moirano, J., C. Brunini, H. Drewes, K. Kaniuth: Realization of a geodetic reference system in Argentina in connection with SIRGAS. Springer, IAG Symposia, No. 118, 199-204, Springer 1998.
Sanchez, L., H. Tremel, H. Drewes: The Colombian national geocentric reference frame. XXII Gen. Ass. IUGG, Birmingham 1999.
Seemüller, W., H. Drewes: Annual report 1997 of the RNAAC SIRGAS. IGS 1997 Technical Reports, 173-174, IGS CB, JPL Pasadena.
Subiza, W.H., R.R. Pérez, F. Barbato, S.M.A. Costa: The redefinition of the geodetic reference system of Uruguay into SIRGAS frame. IAG Symposia, No. 118, 217-222, Springer 1998.
SIRGAS: Final Report Working Groups I and II. IBGE Rio
de Janeiro, 96 pp, 1997.