Luiz Paulo Souto Fortes

The Brazilian Network for Continuous Monitoring of GPS (RBMC): Operation and Products

The Brazilian Network for Continuous Monitoring of GPS (RBMC) is an active geodetic reference network. In this paper its automatic operation and products are described during the first nine months of functioning. It consists of nine permanent GPS stations established in Brazil, in cooperation with many groups. Two of the nine stations (Brasilia and Fortaleza) also belong to the International GPS Service for Geodynamics (GS), while the remaining 7 are integrated into this service by contributing the corresponding data to the SIR IGS Regional Network Associate Analysis Center (RNAAC) located at DGFI (Deutsches Geodaetisches Forschungsinstitut), Germany. The future activities include the densification of the network in the Amazon region (six stations) and in Northeastern and Southern Brazil (one station in each area).

The Vertical Reference Frame for the Americas — The Sirgas 2000 GPS Campaign —

After the excellent results obtained in the establishment of the South American geocentric reference system (SIRGAS) in 1995, which serves mainly for the unification of the national horizontal datums, there was the need of installing also a unified vertical datum. SIRGAS Working Group III was created for this purpose in 1997. The main objectives are to define a unique height reference system, to realize it by a frame of stations, and to connect it with the classical national leveling networks. As a consequence, the SIRGAS 2000 GPS campaign was organized. This campaign served also as a first complete repetition of the 1995 observations in order to determine site velocities. In addition the SIRGAS network was expanded to Central and North America and the Caribbean. About 180 stations were observed during 10 days in May 2000, covering all the area of the Americas.

Accessing the New SIRGAS2000 Reference Frame through a Modernized Brazilian Active Control Network

Since the beginning of its establishment, in December of 1996, the Brazilian Network for Continuous Monitoring of GPS - RBMC has been playing the role as the fundamental geodetic frame in the country, providing users with a direct connection to the Brazilian Geodetic System - SGB. This role has become more relevant with the adoption of the new geodetic system, SIRGAS2000, as of February 25, 2005. In this paper, the current RBMC status is presented, as well as the expansion and modernization plans for its structure, functionality and services to be provided to users. RBMC currently works in post-mission mode, where users are able to freely download from the Internet data collected by each of its 19 stations 24 hours after the observations are collected. The modernization plans specify, in a first step, the network expansion with six additional stations in the Amazon region, including the reactivation of Manaus station, and the connection of all stations to the Internet, to support real time transfer of 1 Hz data to the control center, in Rio de Janeiro. When available at the control center, the data will support WADGPS (Wide Area Differential GPS) corrections to be transmitted, in real time, to users in Brazil and surrounding areas. This new service is under development based on a cooperation signed at the end of 2004 with the University of New Brunswick, supported by the Canadian International Development Agency and the Brazilian Cooperation Agency. It is estimated that users will be able to achieve a horizontal accuracy around 0.5 m (1-σ) in static and kinematic positioning. The expected accuracy for dual frequency receiver users is even better. The availability of the WADGPS service — at no cost -will allow users to tie to the new SIRGAS2000 system in a more rapid and transparent way in positioning and navigation applications. It should be emphasized that support to post-mission static positioning will continue to be provided to users interested in higher accuracy levels.

Modernization and New Services of the Brazilian Active Control Network

The Brazilian Network for Continuous Monitoring of GNSS – RBMC is a national network of continuously operating reference GNSS stations. Since its establishment in December of 1996, it has been playing an essential role for the maintenance and user access of the fundamental geodetic frame in the country. In order to provide better services for RBMC, the Brazilian Institute of Geography and Statistics – IBGE and the National Institute of Colonization and Land Reform – INCRA are both partners involved in the National Geospatial Framework Project – PIGN. This paper provides an overview of the recent modernization phases the RBMC network has undergone highlighting its future steps. These steps involve the installation of new equipment, provide real time data from a group of “core” stations and compute real-time DGPS corrections, based on CDGPS (The real-time Canada-Wide DGPS Service) (The Real-Time Canada-Wide DGPS Service. http://www.cdgps.com/ 2009a). In addition to this, a post-mission Precise Point Positioning (PPP) service has been established based on the current Geodetic Survey Division of NRCan (CSRS-PPP) service. This service is operational since April 2009 and is in large use in the country. All activities mentioned before are based on a cooperation signed at the end of 2004 with the University of New Brunswick, supported by the Canadian International Development Agency and the Brazilian Cooperation Agency. The Geodetic Survey Division of NRCan is also participating in this modernization effort under the same project. This infrastructure of 66 GNSS stations, the real time, post processing services and the potentiality of providing Wide Area DGPS corrections in the future show that the RBMC system is comparable to those available in USA and Europe.

Monitoring the continental reference frame in South America

The South American Terrestrial Reference System (SIRGAS) is defined according to the IERS conventions. The reference frame is realized by a set of three-dimensional geocentric coordinates of about 60 stations derived from a continental GPS campaign in 1995 (epoch 1995.4). The time evolution of station coordinates is defined by the true station motions, in a linear approximation given by the station velocities. These velocities may either be determined from continuous monitoring or from repeated GPS campaigns. The actual continuous monitoring within the IGS Regional Network for South America includes 16 stations on the continent. The linear station velocities derived from two years of observations are presented. As an example of irregular deformations, results from repeated GPS campaigns in a boundary zone along the Caribbean and South American plates are shown. Linear station velocities are estimated as well as unsteady station motions as a consequence of an earthquake. The adequate consideration of these motions in a global geodetic observing system is an important issue.

An Overview of the SIRGAS Project

A general description of the South American Geocentric Reference System (SIRGAS) Project is presented. Since its establishment, in October 1993, the two working groups (“Reference System” and “Geocentric Datum”) of the project have carried out the tasks towards defining a new geocentric reference system and an associated Datum for South America. The achievement of the project objectives were scheduled to be reached on 1997 and the corresponding final reports presented at this LAG Scientific Assembly. This was only possible due to the very high cooperation of many groups, as: the South American countries; IAG, IPGH and NMA, the sponsors; and many others from North America and Europe. The development of the project was based on a continental GPS network, established during a very successful campaign in 1995. With its conclusion, South America has now an unified reference system, with an accuracy compatible with the up to date positioning techniques, what is of a great benefit to all countries in the continent.

Status of the Brazilian Network for Continuous Monitoring of GPS (RBMC)

The current status of the Brazilian Network for Continuous Monitoring of GPS (RBMC) is presented. This network is going to be formed by seven permanent GPS stations in Brazil, established by IBGE in cooperation with other Brazilian institutions. Besides, two IGS stations (Fortaleza and Brasilia) already functioning will be integrated into that structure establishing a set of nine stations in total. This structure is available to the user community that needs GPS L1 & L2 carrier phase and code reference data for post-processing positioning applications as well as for real time applications. It is planned to contribute to IGS network releasing the data of the seven remaining stations. The RBMC stations belong also to the SIRGAS network.

A Contribution to the Geoid Determination

The present period that started at the end of 1980’s with the launch of the first Block II satellites will be certainly marked as the begining of the GPS era.

Brazilian Network for Continuous Monitoring of the Global Positioning System — RBMC

IBGE, as the institution responsible for the Brazilian Geodetic System, presents a proposal for the implementation of a network for continuous monitoring of the Global Positioning System satellites. This network will materialize a three-dimensional geodetic system where users will not occupy the permanent IBGE stations, as the implementation, operation, maintenance, control and data distribution will be under IBGE responsibilities. This network, which has several purposes, will be implemented by steps, with installation of the first nine stations expected to be concluded by the end of next year.

Latest Enhancements in the Brazilian Active Control Network

The Brazilian Network for Continuous Monitoring of GPS – RBMC, since its foundation in December of 1996, has been playing an essential role for the maintenance and user access of the fundamental geodetic frame in the country. It provides to users a direct link to the Brazilian Geodetic System. Its role has become more relevant with the increasing use of space navigation technology in the country. Recently, Brazil adopted a new geodetic frame, SIRGAS2000, in February 2005, fully compatible with GNSS technology. The paper provides an overview of the recent modernization phases the RBMC network has undergone highlighting its future steps. From its current post-mission mode, the RBMC will evolve into a real-time network, providing real-time data and real-time correction to users. The network enhanced with modern GPS receivers and the addition of atomic clocks will be used to compute WADGPS-type corrections to be transmitted, in real time, to users in Brazil and surrounding areas. It is estimated that users will be able to achieve a horizontal accuracy around 0.5 m (1 σ) in static and kinematic positioning and better for dual frequency users. The availability of the WADGPS service will allow users to tie to the new SIRGAS2000 frame in a more rapid and transparent way for positioning and navigation applications. It should be emphasized that support to post-mission static positioning, will continue to be provided to users interested in higher accuracy levels. In addition to this, a post-mission Precise Point Positioning (PPP) service will be provided based on the one currently provided by the Geodetic Survey Division of NRCan (CSRS-PPP). The modernization of the RBMC is under development based on a cooperation signed at the end of 2004 with the University of New Brunswick, supported by the Canadian International Development Agency and the Brazilian Cooperation Agency. The Geodetic Survey Division of NRCan is also participating in this modernization effort under the same project