The special study group SSG 4.188 of IAG was established for the period 1999-2003 during the1999 General Assembly of IUGG in Birmingham, the UK. Its main role within IAG is to provide an official forum for research directed towards mass density modelling. The importance of this topic goes far beyond the narrow scope of work of the study group. There are clear affinities between these research topics in Geology, Geodesy and Solid Earth’s Geophysics. Furthermore, IAG has since many years recognized the importance of this field of research. The present study group is a continuation of previous study groups SSG 4.141 (1991-1995) and SSG 4.170 (1995-1999). This report is a mid-term biannual report on the activities of SSG 4.188.

The members of the study group, both full members and the corresponding members, are spread geographically and with regard to the research interests. Their expertise ranges from mathematical geodesy to geophysics with geological applications. The common point of interest is, however, the realization of the importance in modelling of addressing directly the source of the gravitational signal, the mass density.



Gabriel Strykowski (chairman, Denmark)
Ludwig Ballani (Germany)
Riccardo Barzaghi (Italy) GEOIDE@IPMTF4.TOPO.POLIMI.IT
Fabio Boschetti (Australia) 
Gottfried Gerstbach (Austria)
Petr Holota (chairman of Special Commission of Section IV, Czech Republic)
Bruno Meurers (Austria)
Ove Christian Dahl Omang (Norway)
Spiros Pagiatakis (Canada)
Gabor Papp (Hungary)
Ilya L. Prutkin (Russia)
Tatiana Romanyuk (Russia)
Sabine Schmidt (Germany)
Dan Sharni (Israel)
Vitaly Starostenko (The Ukraine)
Ilias Tziavos (Greece)
Marc Veronneau (Canada)



Corresponding members 

Will Featherstone (chairman of IAG's SSG 3.177, Australia)
Olga Legostayeva (The Ukraine)
Michael Kuhn (Germany)
Irina Makarenko (The Ukraine)
Dimitrios Rossikopoulos (Greece)
Tamara Yegorova (The Ukraine)


Practical work of the study group (1999-2001):


a. New members

Since its creation in 1999 two new members joined SSG 4.188:

Spiros Pagiatakis (Canada) joined as a full member;

Michael Kuhn (Germany) joined as a corresponding member.


b. Website of SSG 4.188

The study group has its own website with the following URL:


c. SSG 4.188 in 1999-2001

The work of the study group as a team suffers from problems that are not uncommon to other study groups. The geographical spread of the members as well as the spread research-wise makes it difficult to collaborate closely on a daily basis. However, such collaboration exists on individual basis between different members of the study group. Also, for all members, it is useful to know about others with similar research interests.

Right from the start we knew that it would be difficult to arrange a meeting for all members of the study group. Not all of us attend necessarily the same conferences, and it would be unfair to arrange a meeting for only part of the study group. Thus, in order to provide means of communication between the members, the idea was to establish and to use the official website of SSG 4.188. Initially we thought that such website could be used for discussions and for exchange of ideas. Regrettably, the website came up only few months ago, and at the present the need for discussions seems to be rather limited. However, this can change in the future and we keep this option open in case somebody takes the initiative. The situation described above is probably very typical and reflects the working conditions of many special study groups. Firstly, it is difficult to share the ideas prior to publishing. Secondly, it takes time to get involved in discussions.

Fortunately, in recent years it became more common for various research groups to promote their work via the Internet. This is also the case for some members of the study group. It is here that we see a realistic possibility in the future of extending the website of SSG 4.188 and to get a realistic picture of the research covered by the study group. All it takes is to provide links from the website of SSG 4.188 to the member’s URL and, possibly, to other related sites. Such procedure will not involve the members with unnecessary additional work, and seem to be a good way of utilizing the Internet without going into trouble of writing special reports.


Scientific results in brief

The website of SSG 4.188 contains a list of relevant recent publications (not necessarily exclusively by the members of the study group) published in 1999-2001 in Journal of Geodesy, Geophysics, Journal of Geophysical Research (volume B), Geophysical Research Letters, Geophysical Journal International, Pure and Applied Geophysics, Physics and Chemistry of the Earth, Tectonophysics and others. Furthermore, this list of publications includes references to relevant presentations and papers at three major conferences: IAG International Symposium on Gravity, Geoid and Geodynamics in Banff in 2000; 70th Annual Meeting of SEG in Calgary 2000, and the 26th General Assembly of EGS in Nice 2001.

The overall impression is, that mass density directly/indirectly still plays an important role in Geodesy, Solid Earth’s Geophysics and Geology. The research activity seems to be spread over the whole spectrum of topics ranging from e.g. the studies of the mathematical structure of the ambiguity domain (i.e. the null-space of the inverse gravimetric problem) to the practical modelling of the regional geology in e.g. the Ukraine or in the United States. Even the old and well-established concepts, e.g. such as the homogenous prism formula for gravitational attraction or similar formulas for other elementary bodies, is still the object of research. The goal is to modify the formulas in order to increase the flexibility (i.e. to use them for more complex mass density modelling) and to improve the speed of computations.

In Geophysics and Geology most of the papers involve mass density models, which are fully 3D. In Geodesy the refinement of terrain corrections, an important step in improving the geoid model, seem still to be a hot topic. Furthermore, the goal of 1-cm geoid makes it worthwhile to investigate the necessity of using more refined mass density models, especially in mountainous areas. Not all countries are like e.g. Switzerland prepared to introduce the refined mass density models into the construction of their national geoids, but more and more countries consider the possibility. In most countries the geoid accuracy of 1-cm is still not achievable. Therefore, the efforts should be concentrated on improving the fundamental data (Digital Elevation Models, gravity information, vertical datum problems) rather than on complicating the geoid modelling by introducing refined mass density information. However, the use of refined mass density models for geoid modelling is without doubt on the agenda for future high accuracy geoids.

Also, in recent years, the launching of CHAMP and the preparations for the new gravity missions GRACE and GOCE boosted the interest not only in gravity and mass density, but also as a mean of studying geophysical phenomena related to e.g. climate changes and similar (oceanography, polar ice melting, postglacial rebound). The expected high accuracy of the new gravity missions seems to make studies of these time-varying phenomena a realistic possibility.


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