Sonia Maria Alves Costa

Improved Analysis Strategy and Accessibility of the SIRGAS Reference Frame

The SIRGAS reference system is at present realized by the SIRGAS Continuously Operating Network (SIRGAS-CON) composed by about 200 stations distributed over Latin America and the Caribbean. SIRGAS member countries are improving their national reference frames by installing continuously operating GPS stations, which have to be consistently integrated into the continental network. As the number of these stations is rapidly increasing, the analysis strategy of the SIRGAS-CON network is based on two hierarchy levels: a) A core network with homogeneous continental coverage and stable site locations ensures the long-term stability of the reference frame. This network is processed by DGFI (Germany) as the IGS RNAAC SIR. b) Several densification sub-networks (corresponding to the national reference networks) improve the accessibility to the reference frame in the individual countries. Currently, the SIRGAS-CON stations are classified in three densification sub-networks (a southern, a middle, and a northern one), which are processed by the SIRGAS Local Processing Centres CIMA (Argentina), IBGE (Brazil), and IGAC (Colombia). These four Processing Centres deliver loosely constrained weekly solutions for the assigned sub-networks, which are integrated in a unified solution by the SIRGAS Combination Centres (DGFI and IBGE). The main SIRGAS products are: loosely constrained weekly solutions in SINEX format for further combinations of the network, weekly positions aligned to the ITRF as reference for GPS positioning in Latin America; and multi-year solutions (positions + velocities) for practical and scientific applications requiring time-dependent coordinates. This paper describes the analysis of the SIRGAS-CON network as the current realization of the SIRGAS reference system, its quality and consistency, as well as the planned activities to continue improving this reference frame.

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).

RBMC in Real Time via NTRIP and Its Benefits in RTK and DGPS Surveys

Currently, IBGE is working on providing new services together with the modernization of the RBMC, such as real-time services via Internet using NTRIP (Networked Transport of RTCM via Internet Protocol), called RBMC-IP and the computation of WADGPS (Wide Area Differential GPS) corrections. A NTRIP caster is in operation at IBGE and receives the streams of 26 stations established in the main cities of Brazil. It is expected to provide real-time data access to all users in the first half-year of 2009. In order to evaluate this new real-time service in terms of precision and accuracy, some tests were performed in Rio de Janeiro state using code and phase observables in static mode. Parameters like distance to the reference stations and the reliability of the connection in urban and rural areas were considered in this evaluation. Another test was performed by the Brazilian Navy during a bathymetric survey with the purpose to update the nautical cartography in an area south of the Brazilian coast, using RTK (Real-Time Kinematic) corrections in RTCM3.0 RTCM means Radio Technical Commission for Maritime Services. (Real-Time GNSS data Transmission Standard). A comparison between NTRIP solution and standard RTK solution using radio link was performed. This paper presents the results of these two experiments and provides an analysis of the advantages, disadvantages and potentialities of this new solution for kinematic and static real-time surveys.

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

The Integration of Brazilian Geodetic Network into SIRGAS — Preliminary Results —

Prior to the advent of satellite positioning, geodetic systems were based on a mathematic model of the Earth which best fits over a specific area. The surveys were developed for mapping requirements where precision of a meter was considered satisfactory. With the adaptation of space positioning techniques by the scientific community, the geodetic systems assumed a global character where centimetric precision could be obtained by these systems. As a consequence of the new technologies, the change from local datum to geocentric reference systems is required, in order to make the information compatible on an international level. To this end Brazil has been involved in the definition of the South American Geocentric Reference System (SIRGAS), whose purpose is to establish a geodetic system for the whole of South America. Brazil will complete the next step to accomplish this change.

THE INTEGRATION OF BRAZILIAN GEODETIC NETWORK INTO SIRGAS

Cooperating as part of South American Geocentric Reference System (SIRGAS), whose purpose is to establish a geocentric reference system for the whole of South America, Brazil will take the next step to continue this change.