Report of the President for the Period 1999 – 2003
Introduction and Objectives
According to the IAG by-laws and the terms of reference,
section IV in the hitherto existing structure of the IAG covers general aspects
of geodetic theory and methodology. In contrast to other lAG
sections, the scope of Section IV is not confined to a specific topic in
Geodesy such as positioning, or gravity field determination, or geodynamics;
the accent here is rather on the systematic (mathematical) treatment of groups
of problems. Therefore it is quite natural that most topics treated by the
bodies in Section IV are shared in one way or another with other lAG sections,
adding a different, more general point of view, but without just duplicating
the work. Ideally, the mathematical problems occurring in the topic-oriented
sections should be reflected upon in Section IV and solved on a general basis.
Another principal scope of Section IV is to develop mathematical tools and to
take up available approaches already developed in other fields of Science and
to adapt them to Geodesy; a prominent historical example is Least Squares
Collocation which was developed in the seventies mainly in Section IV and
nowadays is a basic tool in many branches of Geodesy. In recent years, e.g.
spatial statistics, robust statistical methods, fuzzy theory and the use of
wavelets have been thoroughly investigated in Section IV tor applications in
Geodesy; some of these approaches seem to be very promising and to become
highly efficient tools in geodetic data analysis.
The
principal structure as well as its title was given to Section IV at the 18th
IUGG General Assembly in Hamburg 1983. In 1991 the Special Commission 1 on
„Mathematical and Physical Foundations of Geodesy“ has been added as a new
structure element besides the conventional Special Study Groups. This basic
structure, consisting of Special Commission 1 and Special Study Groups, has
been retained in the past period 1999 – 2003. While the Special Study Groups
have clearly defined topics reflecting the most important aspects of
contemporary geodetic theory, the Special Commission covers broader and
long-term items of geodetic theory in its sub-commissions and working groups.
In order
to achieve its objectives, Section IV has established the following structure
in detail:
President:
Bernhard Heck (Germany)
Secretaries:
Christopher
Jekeli (USA)
Yuanxi
Yang (China)
Special Commission SC1:
Mathematical
and Physical Foundations of Geodesy
Chair:
Petr Holota (Czech Republic)
Subcommission 1:
Statistics and Optimization
Chair:
Peiliang Xu (Japan)
Working Group:
Spatial
Statistics for Geodetic Science
Chair: Burkhard
Schaffrin (USA)
Subcommission 2:
Numerical
and Approximation Methods
Chair:
Willi Freeden (Germany)
Subcommission 3:
Boundary
Value Problems
Chair:
Rüdiger Lehmann (Germany)
Subcommission 4:
Geometry,
Relativity, Cartography, GIS
Chair:
Volker Schwarze (Germany)
Subcommission 5:
Hydrostatic/isostatic
Earth reference Models
Chair: Alexander Marchenko (Ukraine)
In 1999 the following five Special Study Groups have
been established:
SSG 4.187: Wavelets in Geodesy and Geodynamics
Chair: Wolfgang Keller
(Germany)
SSG 4.188: Mass Density from Joint Inverse Gravity Modelling
Chair.
Gabriel Strykowski (Denmark)
SSG 4.189: Dynamic Theories of Deformation and Gravity Fields
Chair: Detlef Wolf (Germany)
SSG 4.190: Non-Probabilistic Assessment in Geodetic Data
Analysis
Chair:
Hansjörg Kutterer (Germany)
SSG 4.191: Theory of Fundamental Height Systems
Chair:
Christopher Jekeli (USA)
In 2001 another Special Study Group has been added:
SSG 4.195: Fractal Geometry in Geodesy
Chair: Erik W. Grafarend (Germany)
A detailied description of the above structure of
Section IV is provided in the Geodesist’s Handbook 2000 (Special Issue of the
Journal of Geodesy, Vol 74, No. 1, pp. 106-115)
The past (and simultaneously the last) four year
period marked a very productive and successful period in the 20 years lifetime
of Section IV, having been involved in many activities of the IAG. The great
progress in geodetic theory and methodology has been made visible in
presentations by Section IV members on the occasion of scientific symposia and
workshops; the scientific work has also been documented by publications in
peer-reviewed international journals such as Journal of Geodesy, Geophysical
Journal International, Journal of Geophysical Research, and others, as well as
in national journals and publication series and in Symposia Proceedings (in
particular in the Springer IAG Symposia series).
Section IV has been represented at many IAG sponsored
symposia and seminars. Only some of the most eminent events are highlighted
below:
·
International Symposium on Gravity, Geoid and Geodynamics in
Banff/Canada, July 31 – August 4, 2000,
· Seventh
International Winter Seminar in Sopron/Hungary, February 19-23, 2001,
· IAG Symposium on
Vertical Reference Systems, Cartagena/Columbia, February 20-23, 2001,
· First International
Symposium on Robust Statistics and Fuzzy Techniques in Geodesy and GIS,
Zurich/Switzerland, March 12-16,2001 (Organized by SSG 4.190),
· IAG Scientific
Assembly in Budapest/Hungary, September 3-7, 2001,
· 5th
Hotine-Marussi Symposium on Mathematical Geodesy in Matera/Italy, July 10-14,
2002 (which was an extremely successful meeting in the series of the
traditional Section IV Symposia),
· W.A. Heiskanen
Symposium in Geodesy in Columbus/Ohio, USA, October 1-5, 2002.
Furthermore, Section IV
contributed significantly to the EGS General Assemblies held in Nice/France on
an annual basis since 2000. Finally, Section IV will be represented at a number
of Symposia and sessions organized on the occasion of the IUGG General Assembly
in Sapporo/Japan, June 30 - July 11. In particular, a profile of the research
activities and a survey of the most important results will be presented in
Symposium G04 „General Theory and Methodology“ organized by Section IV, where
the work of the sub-entities (Special Commission, Special Study Groups) will be
reported, too.
Major scientific achievements have been made in
particular in the various modelling aspects covering physical and mathematical
modelling of geodetic observations as well as stochastic and non-stochastic
methods of data evaluation. Below an attempt is made to provide a short
(probably subjective and biased) summary of the most important steps of
progress:
Physical aspects of modelling in Geodesy are related
to the basic theories of Physics (Newtonian mechanics, theory of relativity,
quantum theory) forming in some way the background of any modelling of geodetic
observations. Significant advances in the past four-year period are visible in
the theory of fundamental reference frames and height systems, in methods for
the description of the Earth’s space-and time-variable gravity field and
deformation, and in modelling the propagation of electromagnetic signals in
refractive media; advanced models in these fields have become necessary due to
the rapid development in the quality and availability of space geodetic
observations.
The mathematical aspects of geodetic modelling refer
to new developments in numerical mathematics and digital signal processing,
including advanced tools such as wavelet analysis in one and two dimensions;
applications in Geodesy range from time series analysis (e.g. polar motion) to
feature extraction and data compression. Special emphasis has also been put
into the formulation and solution of boundary value problems as well as inverse
and improperly posed problems, related e.g. to downward continuation.
Since the foundations of
least squares adjustment by C.F. Gauß stochastic methods of data evaluation
have played a dominant role in Geodesy, in particular in the framework of
quality analysis. Strong progress has been made in the adaption of statistical
inference – including Bayesian statistics – to the fields of Geodesy and
Surveying, digital Photogrammetry and image processing, and digital topography
and cartography. Other topics belonging to this subject are stochastic signal
analysis and geostatistics.
Traditionally and methodologically, a distinction is
made between deterministic and stochastic signals in geodetic observations.
More and more, deterministic signal analysis makes use of wavelet transforms
instead of the classical Fourier techniques. Recently, the spectrum of
uncertainty in geodetic data and models has been extended from the purely
random status; non-random uncertainty of the data can be taken into account using
interval mathematics, fuzzy data analysis and artificial neural networks.
Details about the progress achieved in the past
four-year period can be studied in the reports by the Special Commission 1 and
the Special Study Groups of Section IV that follow in the sequel.
After having worked well for decades, the Section
structure of IAG will be dissolved with the IUGG General Assembly in Sapporo
and fitted to recent requirements and developments. The new IAG structure,
decided at the IAG Scientific Assembly 2001 in Budapest, will bring great
changes concerning the organisation of theoretical and methodological work in
the IAG. The former Section structure, sometimes criticized as inconsistent,
will be replaced by a Commission structure, involving four topic-oriented
commissions. The task of these new commissions is to promote the
advancement of science, technology and international cooperation in their
field. Besides the services, the commissions will form the main scientific
components of the new lAG structure.
In the
new structure an entity like the present section IV is no more foreseen and
visible at the highest level of organization below the EC, the level of the
commissions and services. But this by no means should indicate that geodetic
theory and methodology will not play a fundamental role anymore. Since one of
the major tasks of the new commissions is the promotion of science, these
bodies will be responsible for the development of theory in their respective
fields, too. Of course, this procedure cannot include the development of
general, topic-independent approaches of data analysis and
mathematical-physical foundations, methodology and "general" theory
of Geodesy. After many discussions a solution of this problem could be found
consisting of the creation of the creation of an Inter-Commission Committee on
Theory, reporting directly to the EC. It is expected that the existence of such
a committee will make sure that e.g. mathematically interested geodesists and
application-oriented mathematicians and physicists furthermore will find a home
and meeting-place within IAG.
Furthermore,
the Inter-Commission Committee on Theory should provide a channel of
cooperation amongst the different commissions, on the ground of methodology,
and support a closer collaboration between „theoreticians“ and „practicioners“
in the topic-oriented work of the Commissions. Finally, this Committee is
intended to serve as an interface to other fields of Science, in particular
Mathematics, Physics and Earth Sciences.
Concluding
this general report, I wish to express my sincere thanks to all officers and
colleagues having contributed to the extremely successful work of Section IV in
the past four-year period. It is the work of many scientists in Geodesy,
Mathematics and other branches of Science, often associated with months and
years of great effort, which produced the outstanding results achieved in
Section IV and helped the Section to accomplish its mission for the benefit of
the IAG as a whole. My personal thanks go also to the officers of Section IV
for the excellent cooperation. Finally, it is my sincere wish and hope that
geodetic theory and methodology will find its due position in the new structure
of IAG.