The international symposium Towards an Integrated Global Geodetic Observing System was an initiative of section II Advanced Space Technology of the International Association of Geodesy (lAG). Ittook place in the building ofthe Bavarian Academy of Sciences in Munich from October 5 -9, 1998. About 130 scientists from 24 countries participated in the symposium. It was organized jointly by the Deutsches Geodatisches F orschungsinstitut and the Institut fUr Astronomische und Physikalische Geodasie/Technische Universitat MUnchen. The objective of the symposium was an analysis of the state-of-art of geodetic space techniques and an outlook into the possibility of the establishment of a global integrated observing system. In view of the fact that most geodetic space techniques have reached or approach the one part per billion relative precision level the question arises what their j oint and coordinated operation could offer to the study of system Earth. For this purpose the symposium was divided into four themes, i. e. reference system and datum integration, strength and weakness of space techniques, upcoming gravity field satellite missions, and implications for Earth sciences. Each of these themes was addressed by invited lectures of prominent scientists with sufficient time left for discussion. The oral sessions were complemented by poster sessions. A panel discussion at the closing session completed the program.

The Global Geodetic Observing System (GGOS) has been established by the Int- national Association of Geodesy (IAG) in order to integrate the three fundamental areas of geodesy, so as to monitor geodetic parameters and their temporal varia- ?9 tions, in a global reference frame with a target relative accuracy of 10 or b- ter. These areas, often called ‘pillars’, deal with the determination and evolution of (a) the Earth’s geometry (topography, bathymetry, ice surface, sea level), (b) the Earth’s rotation and orientation (polar motion, rotation rate, nutation, etc. ), and (c) the Earth’s gravity eld (gravity, geoid). Therefore, Earth Observation on a global scale is at the heart of GGOS’s activities, which contributes to Global Change - search through the monitoring, as well as the modeling, of dynamic Earth processes such as, for example, mass and angular momentum exchanges, mass transport and ocean circulation, and changes in sea, land and ice surfaces. To achieve such an - bitious goal, GGOS relies on an integrated network of current and future terrestrial, airborne and satellite systems and technologies. These include: various positioning, navigation, remote sensing and dedicated gravity and altimetry satellite missions; global ground networks of VLBI, SLR, DORIS, GNSS and absolute and relative gravity stations; and airborne gravity, mapping and remote sensing systems.

IAG Symposium, Cairns, Australia, 22-26 August, 2005

It was in September 1906 that the predecessor of the IAG, the 'Internationale Erdmessung', th organized the 15 General Assembly at the Hungarian Academy of Sciences in Budapest. It was 95 years later, in September 2001, that the IAG returned to this beautiful city to hold its Scientific Assembly, IAG 2001, in the historical premises of the Academy. The meeting took place from September 2-7, 2001 and continued the tradition of Scientific Assemblies, started in Tokyo (1982) and continued in Edinburgh (1989), Beijing (1993) and Rio de Janeiro (1997). Held every four years at the midpoint between General Assemblies of the IAG, they focus on giving an integrated view of geodesy to a broad spectrum of researchers and practitioners in geodesy and geophysics. The convenient location of the main building of the Hungarian Academy in downtown Budapest and the superb efforts of the Local Organizing Committee contributed in a major way to the excellent atmosphere of the meeting. As at previous meetings, the scientific part of the program was organized as a series of symposia which, as a whole, gave a broad overview of actual geodetic research activities. To emphasize an integrated view of geodesy, the symposia did not follow the pattern of the IAG Sections, but focussed on current research topics to which several IAG Sections could contribute. Each symposium had 5 sessions with presented papers and poster sessions on two consecutive days.

This series of reference books describes the sciences of different fields in and around geodesy. Each chapter, is written by experts in the respective fields and covers an individual field and describes the history, theory, the objective, the technology, and the development, the highlight of the research, the applications, the problems, as well as future directions. Contents of Volume II include: Geodetic LEO Satellite Missions, Satellite Altimetry, Airborne Lidar, GNSS Software Receiver, Geodetic Boundary Problem, GPS and INS, VLBI, Geodetic Reference Systems, Spectral Analysis, Earth Tide and Ocean Loading Tide, Remote Sensing, Photogrammetry, Occultation, Geopotential Determination, Geoid Determination, Local Gravity Field, Geopotential Determination, Magnet Field, Mobile Mapping, General Relativity, Wide-area Precise Positioning etc.

The Symposium on Vertical Reference Systems (VeReS) was initiated on the occasion of the XXII General Assembly of the International Union of Geodesy and Geophysics (IUGG), Birmingham 1999, by Professor Dr. Wolfgang Torge, Past President of the International Association of Geodesy (lAG) and representative of lAG to the Pan-American Institute of Geography and History (PAIGH). The idea was to organise another joint symposium of lAG and PAIGH like the previous one held during the XX IUGG General Assembly at Vienna, Austria, in 1991. Good reasons for such a joint symposium were the great success and the ongoing activities of the Project on the South American Geocentric Reference System (Sistema de Referencia Geocentrico para America del Sur, SIRGAS) being sponsored by lAG and PAIGH since 1993. The SIR GAS Project (Working Group I) had presented a continental South American reference frame of 58 stations during the lAG Scientific Assembly at Rio de Janeiro, in 1997. This reference frame was already adopted by several South American countries as the basis for their new national horizontal geodetic datums (SIRGAS Working Group II). To overcome the problems of the heterogeneous vertical (height) datums between the individual countries, SIRGAS had installed its Working Group III "Vertical Datum" in 1997. As the discussion on the unification of vertical reference systems is also going on in lAG and other bodies of science and practice, it was decided to dedicate the symposium to this topic.