Reiner Rummel - Böcker

Currently, a first generation of dedicated satellite missions for the precise mapping of the Earth’s gravity field is in orbit (CHAMP, GRACE, and soon GOCE). The gravity data from these satellite missions provide us with very new information on the dynamics of planet Earth. In particular, on the mass distribution in the Earth’s interior, the entire water cycle (ocean circulation, ice mass balance, continental water masses, and atmosphere), and on changes in the mass distribution. The results are fascinating, but still rough with respect to spatial and temporal resolution. Technical progress in satellite-to-satellite tracking and in gravity gradiometry will allow more detailed results in the future. In this special issue, Earth scientists develop visions of future applications based on follow-on high-precision satellite gravimetry missions.

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.

Currently, a first generation of dedicated satellite missions for the precise mapping of the Earth’s gravity field is in orbit (CHAMP, GRACE, and soon GOCE). The gravity data from these satellite missions provide us with very new information on the dynamics of planet Earth. In particular, on the mass distribution in the Earth’s interior, the entire water cycle (ocean circulation, ice mass balance, continental water masses, and atmosphere), and on changes in the mass distribution. The results are fascinating, but still rough with respect to spatial and temporal resolution. Technical progress in satellite-to-satellite tracking and in gravity gradiometry will allow more detailed results in the future. In this special issue, Earth scientists develop visions of future applications based on follow-on high-precision satellite gravimetry 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.

This volume 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, 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 missions. The course was conceived to supply a good theoretical basis in both disciplines, which are deeply involved in the analysis and 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 the radial orbital error, from the point of view of geodesy.

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 text covers all aspects of the solution of the GBVP, from a mathematical basis via geodetic modelling to its relationship with advanced measurements. It provides three foundations to determine the geoid at a one centimetre precision level.

Within the national German geoscientific research and development programme "GEOTECHNOLOGIEN", funded by the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG), the research theme "Observation of the System Earth from Space" was selected as one of 13 key areas in this programme. During the first research phase for this theme from 2002 to 2004 six projects were accomplished covering Earth gravity field and Earth rotation research. These six projects are related to the data exploitation and preparation of analysis techniques for the gravity field satellite missions CHAMP, GRACE and GOCE, to the integration of geodetic observation techniques for a user centre within the International Earth Rotation Service and to improvements in observation and analysis techniques for airborne gravimetry and ring lasers. This book provides a detailed summary of the obtained results, which are relevant for a broad scientific community working in gravity field and Earth rotation research.