Report on IUGG/IAG activities 1995-1999

related to the

Panamerican Institute of Geography and History (PAIGH)

Wolfgang Torge, Hannover

The reporter has been appointed as IAG representative to PAIGH in 1991, and as IUGG liaison officer in 1995.

The International Association of Geodesy (IAG) continued its cooperation with PAIGH, which started through a joint agreement on cooperation signed in 1990. From the previous period, we mention two joint symposia (San Jos! 1990, IUGG Gen. Ass. Vienna 1991) and a jointly organized workshop in Asuncion 1993, together with the US Defense Mapping Agency (now US National Imagery and Mapping Agency NIMA). The latter one was the start of a subcontinent wide project of precise geodetic positioning, which was carried out in the period 1995 - 1999. Within the SIRGAS (Sistema de Referencia Geocentrico para America del Sur) project, a continental geocentric reference frame was established for South America, by cooperation of practically all South American countries, and under the sponsorship of IAG, PAIGH, and NIMA. IAG scientists are represented at the SIRGAS project committee and in the project's working groups.

The SIRGAS Working Group I organized in 1995 an extended GPS observation campaign including 58 sites all over the South American continent. The processing of the observation data was coordinated by the IAG representative and discussed in several international meetings (1996 in Santiago de Chile, 1997 in Isla Margarita, Venezuela). These meetings were financially supported by PAIGH. The results of the processing are precise three-dimensional geocentric station coordinates in the International Terrestrial Reference Frame (ITRF) which is installed and maintained by the IAG International Earth Rotation Service (IERS). The coordinate set was officially released as the final SIRGAS result during the IAG Scientific Meeting in Rio de Janeiro 1997.

An increasing number of SIRGAS sites is being equipped with permanently observing GPS receivers. These stations provide their observation data to the IAG International GPS Service (IGS). They are processed by the Regional Network Associate Analysis Center (RNAAC) which is coordinated by the IAG representative in the SIRGAS Project at Deutsches Geod!tisches Forschungsinstitut (DGFI), Munich, Germany. The continuous monitoring and processing provides thus the maintenance of the SIRGAS reference frame. The SIRGAS coordinates have been adopted as the basis for the national reference networks by several South American countries.

In SIRGAS Working Group II, the national geodetic reference networks of the individual South American countries are installed as a densification of the continental network and in connection with the existing (classical) horizontal networks. The IAG, by means of its official representative and some cooperating institutions (university and research institutes) gave considerable assistance to several countries (Argentina, Brazil, Colombia, Peru, Venezuela).

SIRGAS Working Group III was officially installed during the IAG Scientific Assembly, Rio de Janeiro 1997. Its task is to define and to realize the vertical reference system in connection with the classical levelling networks based on different tide gauges of the South American continent. The first scientific meeting of this Working Group was held in 1998 in Santiago de Chile. The vertical reference system is closely related to the Earth's gravity field (geoid determination, gravity correction of spirit levelling, mean sea level deviation from the geoid at tide gauges). Consequently there is a close cooperation between SIRGAS Working Group III and the IAG International Geoid Service (IGeS).

The IAG Geoid Commission (Subcommission for South America) is collecting gravity data from all South American countries in cooperation with PAIGH in order to improve the geoid determination. All the national geodetic agencies coordinating their activities in the meetings of the "Directores de los Institutos Geograficos de Sudamerica, DIGSA") agreed to provide these data. Several countries started to perform improved geoid computations on the basis on the IAG coordinated procedure. The data base of the precise gravimetric observations in the united Latin American gravity network (RELANG) is maintained by PAIGH and presently moved from Canada (which is no longer a PAIG member) to Colombia. There is a strong interest of IAG (Commission III and Bureau Gravim!trique International, BGI), in this PAIGH activity.

During the period 1995-1999, several scientific and organizational meetings took place, which were sponsored by PAIGH, in coordination with IAG. The outstanding event was the IAG Scientific Assembly in Rio de Janeiro 1997, the first IAG Congress in Latin America at all. An international school on geoid determination was organized by IAG in Rio de Janeiro after the IAG Scientific Assembly. PAIGH not only cooperated in the scientific program organization, but also gave support by travel grants. Financial support by PAIGH to the travel costs was also given to a number of participants (including the IAG representative) at the SIRGAS working group meetings, and to the geoid school in Rio. This is also expected for South American participants at the IAG General Assembly in Birmingham 1999, where special meetings on the SIRGAS and the South American Geoid projects are under preparation.

The intensive activities of IAG in South America and the close cooperation with PAIGH has driven a lot of initiatives in several countries. As a consequence, there has become more awareness of IAG in the continent. In Colombia, which left IUGG in the seventies, there is an actual discussion to return into the Union, driven in particular by the IAG activities.

With respect to the other Associations of IUGG, the result is less favorable. From the six geophysical Associations of IUGG only two responded to a corresponding investigation started by the reporter in 1995. Although a multitude of activities in South America was mentioned, there is obviously no cooperation with PAIGH. No suggestions were made how to eventually establish such a cooperation. Although the PAIGH Secretary General welcomed the appointment of an IUGG liaison officer to PAIGH, there was no reply from the presidents of the PAIGH commissions for Geophysics and Cartography, on the question of how to start an eventual cooperation, and in which areas of common interest.

As a result, the reporter concludes:

It is proposed to abolish the post of an IUGG liaison officer to PAIGH, but to encourage the Associations to appoint Association representatives, in order to exploit the possibilities which obviously exist through a close cooperation, for promoting geodesy and geophysics in South America.