New and more accurate techniques for satellite gravimetry will be available soon, with promising applications in Earth sciences. With this special issue the authors want to stimulate discussion among Earth scientists on objectives and preferences for future satellite gravimetry missions. This is an urgently needed discussion. Visions for follow-on missions have to be developed today, if they are to be realized within 10 years, given the required preparation time of such satellite missions.

In the recent years, space-based observation methods have led to a subst- tially improved understanding of Earth system. Geodesy and geophysics are contributing to this development by measuring the temporal and spatial va- ations of the Earth's shape, gravity ?eld, and magnetic ?eld, as well as at- sphere density. In the frame of the GermanR&D programmeGEOTECHNO- LOGIEN,researchprojectshavebeen launchedin2002relatedto the satellite missions CHAMP, GRACE and ESA's planned mission GOCE, to comp- mentary terrestrial and airborne sensor systems and to consistent and stable high-precision global reference systems for satellite and other techniques. In the initial 3-year phase of the research programme (2002-2004), new gravity ?eld models have been computed from CHAMP and GRACE data which outperform previous models in accuracy by up to two orders of m- nitude for the long and medium wavelengths. A special highlight is the - termination of seasonal gravity variations caused by changes in continental water masses. For GOCE, to be launched in 2006, new gravity ?eld analysis methods are under development and integrated into the ESA processing s- tem. 200,000 GPS radio occultation pro?les, observed by CHAMP, have been processed on an operational basis. They represent new and excellent inf- mation on atmospheric refractivity, temperature and water vapor. These new developments require geodetic space techniques (such as VLBI, SLR, LLR, GPS) to be combined and synchronized as if being one global instrument.

New and more accurate techniques for satellite gravimetry will be available soon, with promising applications in Earth sciences. With this special issue the authors want to stimulate discussion among Earth scientists on objectives and preferences for future satellite gravimetry missions. This is an urgently needed discussion. Visions for follow-on missions have to be developed today, if they are to be realized within 10 years, given the required preparation time of such satellite missions.

In the recent years, space-based observation methods have led to a subst- tially improved understanding of Earth system. Geodesy and geophysics are contributing to this development by measuring the temporal and spatial va- ations of the Earth's shape, gravity ?eld, and magnetic ?eld, as well as at- sphere density. In the frame of the GermanR&D programmeGEOTECHNO- LOGIEN, researchprojectshavebeen launchedin2002relatedto the satellite missions CHAMP, GRACE and ESA's planned mission GOCE, to comp- mentary terrestrial and airborne sensor systems and to consistent and stable high-precision global reference systems for satellite and other techniques. In the initial 3-year phase of the research programme (2002-2004), new gravity ?eld models have been computed from CHAMP and GRACE data which outperform previous models in accuracy by up to two orders of m- nitude for the long and medium wavelengths. A special highlight is the - termination of seasonal gravity variations caused by changes in continental water masses. For GOCE, to be launched in 2006, new gravity ?eld analysis methods are under development and integrated into the ESA processing s- tem. 200,000 GPS radio occultation pro?les, observed by CHAMP, have been processed on an operational basis. They represent new and excellent inf- mation on atmospheric refractivity, temperature and water vapor. These new developments require geodetic space techniques (such as VLBI, SLR, LLR, GPS) to be combined and synchronized as if being one global instrument.

The precise determination of the figure of the earth and its exterior gravitational field requires the solution of the geodetic boundary value problem (GBVP). Recently, a whole series of new measurement techniques has became available, in particular air- and spaceborne methods. They will make its solution much more complete and accurate and will contribute to a better understanding of ocean circulation and of the earth's interior. The book consists of contributions from leading scientists presented at an international summer school. It covers all aspects of the solution of the GBVP, from a mathematical basis via geodetic modeling to its relationship with advanced measurements. It provides three foundations to determine the geoid at a 1-cm precision level.

The book content corresponds to a course of the International Summer School of Theoretical Geodesy held every 4 years under the sponsorship of the International Association of Geodesy. This particular course, that was given at the International Centre for Theoretical Physics in Trieste, has been dedicated to the theory of satellite altimetry as a response to the increasing need of scientific work in this field due to important recent and forthcoming space mission. The course was conceived to supply a good theoretical basis in both disciplines, i.e. geodesy and oceanography, which are deeply involved in the analysis and in the use of the altimetric signal. The main items of interest are the physical theory of ocean circulation, the theory of tides and the ocean time-variability, from the point of view of oceanography and the orbit theory, with particular regard to the formation of the radial orbital error, the so-called cross over adjustment, the analysis of geodetic boundary value problems, the integrated determination of the gravity field and of the radial orbital error, from the point of view of geodesy. All these arguments are treated from the foundation by very-well experts of the various fields, to introduce the reader into the more difficult subjects on which advanced research is currently performed. The peculiarity of the book is in its interdisciplinarity as it can serve to both communities of oceanographers and geodesists to get acquainted with advanced aspects one of the other.

A General Meeting of the lAG was held in Edinburgh, Scotland, to commemorate its 125th Anniversary. The Edinburgh meeting, which attracted 360 scientific delegates and 80 accompanying persons from 44 countries, was hosted jointly by the Royal Society, the Royal Society of Edinburgh and the University of Edinburgh. The scientific part of the program, which was held in the Appleton Tower of the University, included the following five symposia: Symposium 101 Global and Regional Geodynamics Symposium 102 GPS and Other Radio Tracking Systems Symposium 103 Gravity, Gradiometry and Gravimetry Symposium 104 Sea Surface Topography, the Geoid and Vertical Datums Symposium 105 Earth Rotation and Coordinate Reference Frames All together there were 90 oral and 160 poster presentatio'ls. The program was arranged to prevent any overlapping of oral presentations, and thus enabled delegates to participate in all the sessions. The 125th Anniversary Ceremony took place on August 7, 1989, in the noble surroundings of the McEwan Hall where, 53 years earlier, Vening-Meinesz gave one of the two Union Lectures at the 6th General Assembly of the IUGG. The Ceremony commenced with welcome speeches by the British hosts. An interlude of traditional Scottish singing and dancing was followed by the Presidential Address given by Professor Ivan Mueller, on 125 years of international cooperation in geodesy. The Ceremony continued with greetings from representatives of sister societies, and was concluded by the presentation of the Levallois Medal to Professor Arne Bjerhammar.