Geodetic activities in Latin America and The Caribbean: always IN

C Bruninit SIRGAS President

L Sánchez SIRGAS Vice-President

Geodesy has taken several important steps forward since the early days in which it was defined by Helmert as the science devoted to measuring and mapping the Earth’s surface. Today, the challenge of modern Geodesy is to incorporate within Helmert’s definition the determination of many more parameters of the “Earth System”. As in other fields, the continuous and relentless transition from the “old” Geodesy to the “new” Geodesy generates controversial discussions within the geodetic community. One point of view regarding this process was recently proposed by Prof. Chris Rizos in his article “Geodesy: Out with the Old, In with the New”, published in Coordinates (vol. VII, No. 11, November 2011). We have read this article with interest and appreciate the opportunity offered to us by the Coordinates’ Editor to debate the point of view presented there regarding the evolution of Geodesy in different parts of the world. We hope the arguments presented in the following paragraphs provide valuable information regarding the current situation of Geodesy in the Latin America and Caribbean regions.

From Chris’ article we particularly quote the following paragraph: “It must be pointed out however, that the representation of countries from South America, Asia and Africa, as hosts of GNSS tracking stations, as homes to product analysis centres, and on its governance body is disappointing. Nevertheless, some progress is being made with the Asia-Pacific Reference Frame Project (APREF – http://www. ga.gov.au/earth-monitoring/geodesy/ asia-pacific-reference-frame.html), which aims to encourage cross-border cooperation in GNSS geodesy; and the demonstration campaigns being promoted under the auspices of the Multi-GNSS Asia Organisation (MGA – http://www. multignss.asia) to encourage regional experimentation with next generation GNSSs such as the new Japanese QZSS and Chinese BeiDou satellite signals.”

For nearly two decades we have been committed to activities concerning the Geocentric Reference System for the Americas, SIRGAS, which was initiated in 1993 as a South American project with support of the International Association of Geodesy (IAG) and the Pan American Institute of Geography and History (PAIGH), and was recommended by the United Nations’ Cartographic Conference in 2001 to be extended to all American countries. In the new structure of IAG 2003, SIRGAS was integrated as Sub-Commission 1.3b “Regional Reference Frame for South and Central America”. This quite long experience convinced us that the reasons of the somewhat low participation of the Latin-American organisations and their scientists in the global IAG Services that Chris pointed out in his article, should be attributed to cultural reasons (in the broad sense of the word “culture”, the idiom being not a minor limitation), rather than to a real underdevelopment of Geodesy in these regions. Cultural transformations take longer to occur, but along the years we have experienced encouraging progress in most Latin American and Caribbean countries.

SIRGAS has made efforts to build stronger expertise, including organising several training courses to install analysis centres for its Continuously Observing Network of GNSS stations (SIRGASCON), the present realisation of SIRGAS, and the IAG-PAIGH-SIRGAS Schools on Reference Systems. The Schools have been convened during the last three years with local support from the Agustin Codazzi Geographic Institute (Colombia) in 2009, the National Geographic Institute of Peru in 2010, and the National University of Costa Rica in 2011. More than 350 participants from almost all Latin American and Caribbean countries have attended these Schools – a demonstration of the great interest in modern Geodesy. We are confident of attracting even greater participation of geodesists of these regions in the activities being coordinated by the IAG and other international organisations concerned with the production and application of georeferenced data. Fig. 1 summarizes the participation of different countries in the organisational structure of SIRGAS.

At present, SIRGAS-CON consists of more than 240 continuously operating GNSS stations (Fig. 2). Until the first years of this century, most of these stations were installed as part of research projects initiated and funded by foreign institutions, while local scientists were mostly involved in the collection of the data. This situation has changed dramatically during the last decade. Most national mapping/geodetic agencies now understand the need for upgrading their geodetic infrastructure and have begun the deployment of modern GNSS networks, including in many cases with real time capabilities. At present, 14 Latin American countries rely upon SIRGAS to realise their national geodetic reference networks, stations of which are integrated in SIRGAS-CON, and are maintained and data processed following international standards and specifications, particularly those of the International GNSS Service (IGS) and the International Earth Rotation and Reference Systems Service (IERS). Thanks to the operational and administrative efforts of the Latin American institutions responsible for the national reference frames, SIRGAS is today able to make available high quality, long time series observation data of about 40 regional stations, which will be included in the second global IGS reprocessing. This will enable the improvement of the International Terrestrial Reference Frame (ITRF), by strongly linking the northern and southern western hemispheres (Fig. 3).

The installation and management of continuously operating GNSS stations has complemented an intense capacity building process that led to a strong involvement in the analysis of the data produced by SIRGAS-CON (Fig. 4). Today, SIRGAS-CON is divided into different sub-networks that are processed, on a weekly basis, by 8 analysis centres operated by: the Military Geographic Institute of Ecuador, the National University of Cuyo (Argentina), the University of El Zulia (Venezuela), the Brazilian Institute of Geography and Statistics, the Agustin Codazzi Geographic Institute (Colombia), the National Geographic Institute of Argentina, the National Institute of Statistics and Geography (Mexico), and the Military Geographic Service of Uruguay. The processing strategy satisfies all IGS requirements and guarantees that each station is included in three individual solutions. The loosely constrained weekly solutions produced by the analysis centres are combined in a continentally consistent solution aligned to the ITRF by two combination centres, one operated by the Brazilian Institute of Geography and Statistics and the other by the Deutsches Geodätisches Forschungsinstitut (DGFI – Germany). Having two combination centres, functioning independently in different institutions, improves quality control and redundancy of the final products delivered to the community by SIRGAS.

SIRGAS policy promotes the installation of (at least) one analysis centre per country, ensuring the development and sustainability of in-country capabilities to manipulate modern reference frames at the national level. Within this policy, SIRGAS encourages and supports the installation of experimental analysis centres, which are candidates to become SIRGAS analysis centres. During a specified probation period, they align their processing strategies to those required by SIRGAS and demonstrate their capacity for timely and regular delivery of weekly solutions. Once they satisfy these requirements, they may be appointed as official analysis centres. During this test period (at least one year), they process a set of SIRGASCON stations, however their solutions are not included in the computation of the final SIRGAS-CON products. Presently, the Military Geographic Institute of Chile is an experimental analysis centre, and the Geographic Institute of Bolivia and the National University of Costa Rica are this year preparing to become experimental processing centres.

SIRGAS contributes to the IGS through the IGS Regional Network Associate Analysis Centre for SIRGAS (IGSRNAAC- SIR), operated by the DGFI. Since 1996 this centre delivers loosely constrained weekly solutions, that are combined together with those generated by the other global and regional IGS analysis centres, to form the IGS Polyhedron. In addition, state-of-theart multi-year solutions for the SIRGAS reference frame have been computed on an almost yearly basis (Fig. 5, Fig. 6).

Since 2006, SIRGAS operates a service for computing regional ionospheric maps based on SIRGAS-CON observations (Fig. 7 ). The ionospheric model used by SIRGAS has evolved from a “thin layer” simplification for computing the integrated electron density to a formulation that represents the four-dimensional distribution of the electron density of the E, F1, F2 and top-side ionospheric layers. The SIRGAS maps of vertical Total Electron Content are being used for kind of studies, such as validating the International Reference Ionosphere (IRI) over the South American region, improving the performance of single-frequency GPS receivers, and testing the feasibility of computing the ionospheric corrections for a regional satellite based augmentation system (SBAS). SIRGAS is also contributing to the modernisation of the classical vertical reference systems. The main objective is to refer all existing physical heights to one and the same equipotential surface, which has to be defined and realised in a global frame with high precision. This demands a close collaboration with all colleagues working worldwide on this topic. During the four coming years, SIRGAS is participating in GGOSTheme 1 (Unified Global Height System) through activities carried out within the joint working group “Vertical Datum Standardisation”, a common effort of the Global Geodetic Observing System, the IAG Commission 2 (Gravity Field) and the International Gravity Field Service (IGFS).

Besides the SIRGAS participation in the IAG Commission 1 (as Sub-Commission 1.3b), the IGS-RNAAC-SIR and GGOS-Theme 1, SIRGAS contributes to the IAG Commission 1 working group on “Integration of Dense Velocity Fields into the ITRF”, the IGS working group TIGA, the IAG Commission 1 working group on “Deformation Models for Reference Frames”, the IAG Commission 1-IERS-ICTT joint working group “Strategies for Epoch Reference Frames”, and the IAG Commission 4 study group “Ionosphere Modelling and Analysis”. Up-to-date and detailed information about SIRGAS, its achievements and challenges, can be obtained from the organisation’s web page (www.sirgas.org) and, among others, the following papers recently published in S. Kenyon, M.C. Pacino, U. Marti (Eds.), “Geodesy for Planet Earth”, IAG Symposia, Vol. 136, Springer 2012:

Brunini, C., F. Azpilicueta, M. Gende, A. Aragón-Ángel, M. Hernández-Pajares, J.M. Juan, J. Sanz: Toward a SIRGAS Service for Mapping the Ionosphere’s Electron Density Distribution, 753-760.

Brunini, C., L. Sánchez, H. Drewes, S. Costa, V. Mackern, W. Martínez, W. Seemüller, A. da Silva: Improved Analysis Strategy and Accessibility of the SIRGAS Reference Frame, 3-10.

Costa, S.M.A, A.L. Silva, J.A. Vaz: Processing Evaluation of SIRGAS-CON Network by IBGE Analysis Center, 859-867.

Costa, S.M.A., A.L. Silva, J.A. Vaz: Report on the SIRGASCON Combined Solution by IBGE Analysis Center, 853-858.

Drewes, H., O. Heidbach: The 2009 Horizontal Velocity Field for South America and the Caribbean, 657-664.

Sánchez, L., W. Seemüller, M. Seitz: Combination of the Weekly Solutions Delivered by the SIRGAS Processing Centres for the SIRGASCON Reference Frame, 845-852.

Seemüller, W., M. Seitz, L. Sánchez, H. Drewes: The new Multi-year Position and Velocity Solution SIR09P01 of the IGS Regional Network Associate Analysis Centre (IGS RNAAC SIR), 877-884.