2003-12-09

The Inter-Commission Committee on Theory (ICCT) (2007-2011)

The InterCommission Committee on Theory (ICCT) was formally approved and established after the IUGG XXI Assembly in Sapporo, 2003, to succeed the former IAG Section IV on General Theory and Methodology and, more importantly, to interact actively and directly with other IAG entities.

President: Nico Sneeuw (Germany)

Vice President: Pavel Novák (Czech Republic)

Terms of Reference

The InterCommission Committee on Theory (ICCT) was formally approved and established after the IUGG XXI Assembly in Sapporo, 2003, to succeed the former IAG Section IV on General Theory and Methodology and, more importantly, to interact actively and directly with other IAG entities. As a result of this restructuring, and recognizing that geodetic observing systems have advanced to such an extent that geodetic measurements (i) are now of unprecedented accuracy and quality, can readily cover a region of any scale up to tens of thousands of kilometres, yield non-conventional data types, and can be provided continuously; and (ii) consequently, demand advanced mathematical modelling in order to obtain the maximum benefit of such technological advance, the ICCT
(1) strongly encourages frontier mathematical and physical research, directly motivated by geodetic need/practice, as a contribution to science/engineering in general and the foundations of geodesy in particular;
(2) provides the channel of communication amongst the different IAG entities of commissions/services/projects on the ground of theory and methodology, and directly cooperates with and supports these entities in the topic-oriented work;
(3) helps the IAG in articulating mathematical and physi-cal challenges of geodesy as a subject of science and in attracting young talents to geodesy. The ICCT should strive to attract and serve as home to mathematically motivated/oriented geodesists and to applied mathema-ticians; and 
(4) encourages closer research ties with and gets directly involved in relevant areas of the Earth sciences, bearing in mind that geodesy has been always playing an impor-tant role in understanding the physics of the Earth.

Objectives

The main objectives of the ICCT are

  • to be the international focal point of theoretical geodesy,
  • to encourage and initiate activities to further geodetic theory,
  • to monitor research developments in geodetic modelling.

To achieve these objectives, the ICCT interacts and collaborates with the IAG Commissions and other IAG related entities (services, projects).

Structure

The structure of InterCommission Committees is specified in the IAG by-laws. The ICCT steering committee consists of the President, the Vice-President and a repre-sentative from each of the Commissions.  ICCT activities are undertaken by study groups. By the inter-commission nature of the ICCT, these study groups are joint study groups, affiliated to one or more of the Commissions.

Inter-Commission Study Groups

The following list names the Inter-Commission Study Groups. Their chairpersons are indicated in boldface. The numbers behind the names denote the affiliation to the individual Commissions in order of precedence.

IC-SG1: Theory, Implementation and Quality Assess-ment of Geodetic Reference Frames (joint with Commission 1, IERS)
Athanasios Dermanis (Greece) 

IC-SG2: Quality of Geodetic Multi-Sensor Systems and Networks (joint with Commissions 4, 1)
Hansjörg Kutterer (Germany)

IC-SG3: Configuration Analysis of Earth Oriented Space Techniques (joint with Commissions 3, 2, 1)
Florian Seitz (Germany)

IC-SG4: Inverse Theory and Global Optimization (joint with Commission 2)
Christopher Kotsakis (Greece)

IC-SG5: Satellite Gravity Theory (joint with Commission 2)
Torsten Mayer-Gürr (Germany)

IC-SG6: InSAR for Tectonophysics (joint with Commissions 3, 4)
Masato Furuya (Japan)

IC-SG7: Temporal Variations of Deformation and Gravity (joint with Commissions 3, 2)
Detlef Wolf (Germany)

IC-SG8: Towards cm-accurate Geoid – Theories, Computational Methods and Validation (joint with Commission 2)
Y. M. Wang (USA)

Program of Activities

The ICCT's program of activities will include

  • participation as (co-)convener of geodesy sessions at major conferences (IAG, EGU, AGU, …),
  • organization of a Hotine-Marussi symposium,
  • initiation of a summer school on theoretical geodesy,
  • maintaining a website for dissemination of ICCT related information.

Steering Committee

President Nico Sneeuw, Germany

Vice-President Pavel Novák, Czech Republic

Representatives:

  • Commission 1 - Zuheir Altamimi, France
  • Commission 2 - Pieter Visser, The Netherlands
  • Commission 3 - Richard Gross, USA
  • Commission 4 - Sandra Verhagen, The Netherlands
  • GGOS - TBD

Intercommission Study Groups

IC-SG1 Theory, Implementation and Quality Assessment of Geodetic Reference Frames

Chair: A. Dermanis (Greece) 

Affiliation: Commission 1, IERS

Introduction

The realization of a reference system by means of a reference frame, in the form of coordinate time series or coordinate functions for a global set of control stations is a complicated procedure. It involves input data from various space techniques each one based on its own advanced modelling and observation analysis techniques, as well as, criteria for the optimal selection of the time evolution of the reference frame among all data compatible possibilities. The relevant "observed" coordinate time series demonstrate significant signals of periodic, non- periodic variations and discontinuities, which pose the challenge of departing from the current ITRF model of linear time evolution, realized by reference epoch coordinates and constant velocities. The final product needs proper quality measures, which take also into account the possible modelling discrepancies, systematic errors and noise level of each particular space technique. The connection with a celestial frame by means of earth orientation parameters (EOPs) and current geophysical plate motion hypotheses necessitate the study of the compatibility of the geodetically established reference system with reference systems introduced in theoretical studies of the earth rotation and in theoretical geophysics. The working group is primarily aiming in problem identification, outlining of possible solution directions and motivation of relevant scientific research.

Objectives

  • Study of models for time-continuous definitions of reference systems for discrete networks with a non-permanent set of points and their realization through discrete time series of station coordinate functions and related earth rotation parameters.
  • Understanding the relation between such systems and reference systems implicitly introduced in theories of earth rotation and deformation.
  • Extension of ITRF establishment procedures beyond the current linear (constant velocity) model, treatment of periodic and discontinuous station position variations, understanding of their geophysical origins and related models.
  • Understanding the models used for data treatment within each particular technique, identification of possible biases and systematic effects and study of their influence on the combined ITRF solution. Study and improvement of current procedures for the merging of data from various space techniques.
  • Statistical aspects of reference frames, introduction and assessment of appropriate quality measures.
  • Problems of mathematical compatibility within current celestial-to-terrestrial datum transformations and proposal of new conventions which are data-based and theoretically compatible.
  • Program of Activities
  • Launching of a webpage for dissemination of information, presentation, communication, outreach purposes, and providing a bibliography.
  • Working meetings at international symposia and pre-sentation of research results in appropriate sessions.
  • Organization of workshops dedicated mainly to problem identification and motivation of relevant scientific research.
  • A special issue of the Journal of Geodesy on reference frames with papers from working group workshops and invited review papers.

Membership

  • Athanasios Dermanis, Chair (Greece)
  • Zuheir Altamimi (France)
  • Hermann Drewes (Germany)
  • Fernando Sansò (Italy)
  • Claude Boucher (France)
  • Gerard Petit (France)
  • Xavier Collilieux (France)
  • Axel Nothnagel (Germany)
  • Erricos Pavlis (USA)
  • Jim Ray (USA)
  • Frank Lemoine (USA)
  • Geoff Blewitt (USA)

(some members to be confirmed still)

IC-SG2 Quality of Geodetic Multi-Sensor Systems and Networks

Chair: H. Kutterer (Germany)

Affiliation: Commissions 4, 1

Introduction

Modern geodetic observations are usually embedded in an integrated approach based on multi-sensor systems and networks. The fields of application are as manifold as the sensors in use. For example, total stations, GPS receivers and terrestrial laser scanners are applied in engineering geodesy for structural monitoring purposes together with permanently installed equipment. Geometric and physical space-geodetic sensors may serve as a second example since they are used for the determination of global reference frames.

It is good geodetic tradition to assess the quality of the obtained results for further use and interpretation. However, each field of application provides its own quality standards which are to some extent incomplete regarding the immanent processes. At present, there is no general methodology available for the theoretically founded quality assessment of geodetic multi-sensor systems and networks and of the induced processes.

The main focus of the SG is on the methodological foun-dation of quality in the context of close-range applica-tions in engineering geodesy. Typical properties of the systems and networks considered here are on the one hand their readiness for real-time application and their adaptivity to observed system and process variations. On the other hand the systems and networks as well as their input are uncertain which limits analysis, interpretation and control. The IC SG2's work will cover at least three main fields in this context:
(1) Identification and mathematical definition of the relevant process-related uncertainty and quality properties and models, propagation and inference,
(2) revision, quality-related extension, and comparison of different approaches for the state space prediction and filtering (e.g., Kalman and shape filters, Bayesian filters, particle filters, fuzzy filters),
(3) validation studies using applications of broader geo-detic interest such as geodetic monitoring, mobile mapping, machine control.

Comparable work outside geodesy both in the engineer-ing and mathematical communities and in international standardization will be taken into account.

Objectives

The main objectives of the IC SG2 are

  • to derive and promote a terminology and methodology for the quality assessment of geodetic multi-sensor systems and networks,
  • to provide a unique platform for quality-related issues in geodesy and neighbouring fields,
  • to initiate extended studies on related probabilistic and non-probabilistic methods for interpretation and decision,
  • to monitor parallel developments in other communities.

To achieve these objectives, the IC SG 2 interacts and collaborates with the ICCT and its entities as well as the IAG Commissions 4 and 1. 

The SG's work will be distributed to IAG sister organiza-tions through respective members.

Members

TBC

Program of Activities

The IC SG2s program of activities will include

  • organization of SG meetings and of a scientific work-shop on quality issues
  • participation in respective symposia,
  • maintaining a website for quality-related information,
  • supporting contributions to the ICCT activities.

IC-SG3 Configuration Analysis of Earth Oriented Space Techniques

Chair: F. Seitz (Germany) 

Affiliation: Commissions 3, 2, 1

Introduction

Activities of the study group are focussed on modern methods of Earth observation from space. Today a multitude of simultaneously operating satellite systems with different objectives are available. They offer a broad spectrum of information on global and regional-scale processes within and/or between individual components of the Earth system in different temporal resolutions.

The general objective of this study group is the develop-ment of strategies how complementary and redundant information from heterogeneous observation types can be combined and analysed with respect to physical processes in the Earth system.

Most of the measurement techniques are restricted to the observation of integral effects of a multitude of under-lying geophysical processes. It shall be investigated in which way the combination of heterogeneous data sets allows for the separation of processes and the identifica-tion of individual contributors.

In particular the studies span geometrical observation techniques (e.g. point positioning systems, imaging radar systems), gravimetrical observation techniques (e.g. GRACE, GOCE) and sensors which allow for the direct observation of individual physical processes (e.g., IceSat, SMOS).

The combination of complementary and redundant observation types fosters and improves the understanding of the Earth system. This implies more reliable information on processes and interactions in the subsystems of the Earth which is especially necessary with regard to studies of global change.

Among the most important steps are compilation and assessment of background information for individual systems and sensors (mode of operation, sensitivity, accuracy, deficiencies) as well as theoretical studies which (new) information on the Earth system can be gained from a combination of different observation methods.

Objectives

  • which processes in the Earth system are insufficiently known and which parameters are imprecisely determined?
  • can the understanding of individual processes be improved by common analysis of different observa-tions types?
  • which are the target parameters and how are the connections with other variables?
  • which sensors are available and sensitive for the target parameters?
  • which sensors can be used to reduce unwanted signals?
  • which are the accuracies, temporal and spatial resolu-tions of the different data sets and which regions and time spans are covered?
  • are the data publicly available or is their access re-stricted?
  • which pre-processing steps are necessary in order to extract the proper information from the raw observa-tion data?
  • have the data already been pre-processed? Which methods, models and conventions have been applied? Are there possible error sources or inconsistencies?
  • which methods can be applied in order to enhance the information content (e.g. filters)?
  • how can the heterogeneous observation types can be combined expediently?
  • how do the observation equations look like?
  • which methods for parameter estimation can be ap-plied? How can linear dependencies between para-meters and rank deficiency problems be solved?
  • how can balance equations be regarded in the combi-nation process (e.g. mass and energy balance)?
  • are there additional information (models and terrestrial data) which can/must be considered?
  • which of the desired parameters can be assessed with the available observation techniques?
  • which further parameters are desired and how could appropriate missions for the future look like?

The research activities shall be coordinated between the participating scientists and shall be conducted in inter-disciplinary collaboration. At all times the group is open for new contacts and members in order to embed the activities in a wide context.

IC-SG4 Inverse Theory and Global Optimization

Chair: C. Kotsakis (Greece) 

Affiliation: Commission 2

Introduction

At the Sapporo IUGG General Assembly (June 30 - July 11, 2003), the International Association of Geodesy (IAG) has approved the establishment of an ‘inter-commission' working group (WG) on Inverse Problems and Global Optimization, with the aim of supporting and promoting theoretical and applied research work in vari-ous areas of modern geodetic data analysis and inversion. This WG has successfully operated during the last four years under the umbrella of the Intercommission Committee on Theory (ICCT) and the chairmanship of Dr. Jürgen Kusche. During the IAG-EC meeting at the Perugia IUGG General Assembly (July 2 – 13, 2007) the new structure of the ICCT and its associated WG’s was discussed, and a decision was made that the ICCT/WG on Inverse Problems and Global Optimization will continue its operation for another 4-year period. The purpose of this document is to give an (updated) description of the WG's potential study areas and research objectives, and its associated terms of reference for the upcoming research period 2007 - 2011.

Terms of Reference

It is well recognized that many, if not most, geodetic problems are in fact inverse problems: we know to a certain level of approximation the mathematical and physical models that project an Earth-related parameter space and/or signal onto some data space of finite discrete vectors; given discrete noisy data we then want to recover the governing parameter set or the continuous field (signal) of the underlying model that describes certain geometrical and/or physical characteristics of the Earth. The situation is further complicated by the fact that these problems are often ill-posed in the sense that only generalized solutions can be retrieved (due to the existence of non-trivial null-spaces) and/or that the solutions do not depend continuously on the given data thus giving rise to dangerous unstable solution algorithms. In order to deal successfully with geodetic data inversion and parameter/signal estimation problems, it is natural that we have to keep track with ongoing developments in inverse problem theory, global optimization theory, multi-parameter regularization techniques, stochastic modelling, Bayesian inversion methods, statistical estimation theory, data assimilation, and other related fields of applied mathematics. In modern geodesy we also have to develop special inversion techniques that can be used for large-scale problems, involving high degree and order gravity field models from space gravity missions and high-resolution discretizations of the density field or the dynamic ocean topography.

Earth's gravity field modelling from space gravity missions has been (and will surely continue to be in the future) a key study area where existing and newly devel-oped tools from Inverse Problem Theory need to be implemented (including the study of regularization methods and smoothing techniques and the quality assessment of Earth Gravity Models, EGMs). With the cutting-edge applications of the latest and upcoming gravity missions (recovery of monthly surface mass variations from GRACE, constraining viscosity/litho-spheric/postglacial rebound models from GRACE time-variable gravity and from GOCE static geoid pattern analysis), it can be expected that Inverse Problem Theory will increase its importance for the space gravity commu-nity.

Furthermore, there still exist other, more classical geodetic problems that have been identified as inverse and ill-posed and have traditionally attracted the interest of many researchers: the inverse gravitational problem where we are interested in modelling the earth's interior density from gravity observations, various types of downward continuation problems in airborne/satellite gravimetry and geoid determination, certain problems in the context of satellite altimetry and marine gravity modelling, the problem of separating geoid and dynamic ocean topography, the problem of inferring excita-tions/earth structure parameters from observed polar mo-tion, the determination of stress/strain tensors from observational surface monitoring data, or certain datum definition problems in the realization of global geodetic reference systems. Another, relatively recent, geodetic problem of ill-posed type is the orbit differentiation problem: non-conventional gravity recovery methods like the energy conservation approach and the acceleration approach require GPS-derived kinematic satellite orbits to be differentiated in time, while counteracting noise amplification at the same time. The above non-exhaustive list of inverse problems provides a rich collection of study topics with attractive theoretical/practical aspects, which (in conjunction with the increasing data accuracy, coverage and resolution level) contain several open issues that remain to be resolved.

Objectives

The aim of the WG is to bring together people working on inverse problem theory and its applications in geodetic problems. Besides a thorough theoretical understanding of inverse problems in geodesy, the WG's central research issue is the extraction of maximum information from noisy data by properly developing mathematical/statistical methods in a well defined sense of optimality, and applying them to specific geodetic problems. In par-ticular, the following key objectives are identified:

  • Identification and theoretical understanding of inverse and/or ill-posed problems in modern geodesy
  • Development and comparison of mathematical and statistical methods for the proper treatment of geodetic inverse problems
  • Recommendations and communication of new inver-sion strategies

More specific research will focus, for example, on global optimization methods and theory, on the mathematical structure of null-spaces, on the treatment of prior information, on nonlinear inversion in geodetic problems and on the use of techniques for treating inverse problems locally. It is also necessary to investigate the quality assessment and numerical implementation of existing regularization methods in practical geodetic problems (e.g. dealing with coloured noise and/or heterogeneous data, using partially over- and underdetermined models, dealing with different causes of ill-pose like data gaps and downward continuation, coping with data sets that have entirely unknown noise characteristics, etc.).

Membership

The following is a proposed (tentative) membership list for the IAG/ICCT WG on Inverse Problems and Global Optimization. The final list will be confirmed within 2007.

  • C. Kotsakis (Greece, chair)
  • J. Kusche (Germany)
  • S. Baselga Moreno (Spain)
  • J. Bouman (The Netherlands)
  • P. Ditmar (The Netherlands)
  • B. Gundlich (Germany)
  • P. Holota (Czech Republic)
  • M. Kern (The Netherlands)
  • T. Mayer-Gürr (Germany)
  • V. Michel (Germany)
  • P. Novak (Czech Republic)
  • S. Pereverzev (Austria)
  • B. Schaffrin (USA)
  • M. Schmidt (Germany)
  • Y. Shen (China)
  • N. Sneeuw (Germany)
  • S. Tikhotsky (Germany)
  • C. Xu (Russia)

Program of Activities

The WG's activities will include the launching of a webpage for dissemination of information, for presentation, communication and monitoring of research results and related activities, and for providing an updated bibliographic list of references for relevant papers and reports in the general area of geodetic inverse problems. This would also provide WG's members (and other interested individuals) with a common platform to communicate individual views and results, and stimulate discussions. Although the discussion will be in general based on e-mail, it is planned to have splinter meetings during international conferences and, if possible, a workshop or a special conference session.

IC-SG5 Satellite Gravity Theory

Chair: T. Mayer-Gürr (Germany) 

Affiliation: Commission 2

Members

  • Torsten Mayer-Gürr, University of Bonn, Germany – tmg@geod.uni-bonn.de
  • Oliver Baur, University Stuttgart, Germany – baur@gis.uni-stuttgart.de
  • Wolfgang Bosch, DGFI, Germany – bosch@dgfi. badw.de
  • Pavel Ditmar, TU Delft, Netherlands – ditmar@geo.tudelft.nl
  • Thomas Gruber, TU Munich, Germany – thomas.gruber@bv.tu-muenchen.de
  • Shin-Chan Han, NASA GSFC, USA – schan@puuoo. gsfc.nasa.gov
  • Michael Kern, ESTEC, Netherlands – michael.kern@esa.int
  • Jürgen Kusche, GFZ Potsdam, Germany – jkusche@gfz-potsdam.de
  • Michael Schmidt, DGFI, Germany – schmidt@dgfi.badw.de
  • Roland Schmidt, GFZ Potsdam, Germany – rschmidt@gfz-potsdam.de
  • Roland Pail, TU Graz, Austria – pail@geomatics.tu-graz.ac.at
  • Insa Wolf, University of Hannover, Germany – wolf@ife.uni-hannover.de

Objectives

  • Gravity field estimation
  • Perturbation techniques versus in-situ measurements and new approaches like short-arc integration, energy balance and so on.
  • Computational problems related to the huge quantities of data. Algorithms to divide the computational tasks to run on massive parallel systems.
  • Noise and error treatment
  • Estimating the variance-covariance matrices of the observations, filtering techniques.
  • Integrated analysis of different sensors featuring indi-vidual noise characteristics (like Accelerometer and K-band sensor in case of GRACE), calibration of instruments (internal and external).
  • A-posteriori variance-covariance matrices, error propagation, validation.
  • Space-time resolution, de-aliasing. Which signals can be estimated and which must be modelled?
  • Gravity field modelling
  • Choice of basis functions in time and space (with respect to applications in hydrology, oceanography).
  • Global and regional modelling, modelling in terms of gravity sources (mass variations).
  • Reference systems and datum problems (origin, orientation, static and temporal datum systems for gravity field changes).
  • Aspects of data combination
  • Combination of the satellite gravity missions (CHAMP, GRACE and GOCE) with terrestrial and aerial gravity information.
  • Combination at the data level versus combination of results.
  • A-priori information from non-gravity data such as changes in the geometry of the Earth and its rotation.
  • Unified approaches: Joint analysis of gravity field observations, Earth rotation, and geometry changes.
  • Future satellite missions
  • Theory of new observation types and instruments.
  • Formation flights. Investigation into stability of satel-lite formations and their sensitivity to aliasing errors.
  • Follow-on gravity field missions.
  • Orbit determination: theory, perturbation techniques, stability problems.
  • Challenges caused by the increasing accuracy of the observations: integration techniques, numerical prob-lems due to limited digits in computation.

Activities

  • Email: Internal email discussions
  • Meeting: Organization of working group meeting at larger meetings.
  • Website: Launch of a website for communications, information and links to data sources
  • Simulation data: Assemble of a simulated data set with orbits, background models and artificial noise. This data set serves to test new algorithms and make different approaches comparable.

IC-SG6 InSAR for Tectonophysics

Chair: M. Furuya (Japan) 

Affiliation: Commissions 3, 4

Members (tentative)

  • Masato Furuya (chair), Hokkaido University, Japan, furuya@mail.sci.hokudai.ac.jp
  • Falk Amelung, University of Miami, USA,
  • Roland Bürgmann, UC Berkeley, USA
  • Andrea Donnellan, JPL, USA
  • Yuri Fialko, SIO/UCSD, USA
  • Yo Fukushima, Kyoto University, Japan, yofuku-shima@rcep.dpri.kyoto-u.ac.jp
  • Sigrujon Jónsson, ETH, Switzerland, sj@erdw.ethz.ch
  • Zhenhong Li, University College London, UK
  • Zhong Lu, USGS, USA
  • Taku Ozawa, NIED, Japan
  • Matthew Pritchard, Cornell University, USA
  • David Sandwell, SIO/UCSD, USA
  • Masanobu Shimada, EORC/JAXA, Japan
  • Mark Simons, Caltech, USA
  • Tim Wright, Leeds University, UK

Introduction

Against a backdrop of a series of SAR satellite missions, ERS1/2, JERS, Envisat/ASAR, ALOS/PALSAR, Radar-sat-1/2, TerraSAR/X, planned future missions (e.g. Centinel-1 and Desdyni), the overall objective of this working group is to be a focus of activities in the follow-ing research areas, related to geodetic measurement and analysis of SAR/InSAR data and their application to tectonophysical problems.

Objectives

  • SAR/InSAR data analysis for tectonophysics: Development of new analysis techniques: e.g., Scan-SAR interferometry, PS-InSAR, SBAS approach, Polarimetric InSAR etc..
  • Retrieval and separation of atmospheric and crustal deformation signal: Improvement of conventional approaches (stacking or calibration), and development of a brand-new approach
  • Modelling and interpretation of SAR/InSAR data: Development, application and assessment of geo-physical modelling of InSAR data: e.g., efforts to go beyond over-simplified static solutions.
  • Combination of InSAR data with other measurement sources: Development of novel and useful combination of InSAR data with other measurement techniques, such as GPS, gravity, seismogram etc.

Activities

  • Email: Internal email discussions
  • Meeting: Organization of working group meeting and organization of sessions at larger meetings. Potential candidate venues are the Joint AGU/CGU meeting, IAG workshops, FRINGE workshop, etc.
  • Website: Launch of a website for communications, information dissemination and links to data sources
  • Monitoring: Monitoring and presentation of activi-ties—either by WG members or external—that are going on in these areas.

IC-SG7 Temporal Variations of Deforma-tion and Gravity

Chair: D. Wolf (Germany) 

Affiliation: Commissions 3, 2

Introduction

Recent advances in ground-, satellite- and space-geodetic techniques have detected temporal variations of deformation and gravity with unprecedented accuracy over a wide period range. These variations are related to various surficial and internal earth processes. The new types of observational data require the development of 2-D/3-D earth models and novel interpretational techniques.

Program of Activities

  • Development of 2D/3-D elastic/viscoelastic earth models for simulating processes responsible for defor-mation and gravity variations.
  • Forward modelling of deformation and gravity varia-tions caused by atmospheric, cryospheric, hydro-spheric or internal forcing functions.
  • Inverse modelling of observed deformation and gravity variations in terms of forcing functions or in terms of elastic/viscoelastic earth parameters.

Membership

  • H. Abd-Elmotaal (Egypt) abdelmotaal@lycos.com
  • M. Bevis (USA) mbevis@osu.edu
  • A. Braun (Canada) braun@geomatics.ucalgary.ca
  • L. Brimich (Slovakia) geofbrim@savba.sk
  • D. Carbone (Italy) carbone@ct.ingv.it
  • B. Chao (USA) bfchao@ncu.edu.tw
  • J. Fernandez (Spain) jose_fernandez@mat.ucm.es
  • L. Fleitout (France) fleitout@geologie.ens.fr
  • P. Gonzales (Spain) pjgonzal@mat.ucm.es
  • E. Ivins (USA) eri@fryxell.jpl.nasa.gov
  • V. Klemann (Germany) volkerk@gfz-potsdam.de
  • Z. Martinec (Czech Rep.) zdenek@gfz-potsdam.de
  • G.A. Milne (UK) g.a.milne@durham.ac.uk
  • J. Müller (Germany) mueller@ife.uni-hannover.de
  • Y. Rogister (France) Yves.Rogister@eost.u-strasbg.fr
  • H.-G. Scherneck (Sweden) hgs@oso.chalmers.se
  • G. Spada (Italy) giorgio.spada@gmail.com
  • W. Sun (Japan) sunw@eri.u-tokyo.ac.jp
  • Y. Tanaka (Japan) ytanaka@gsi.go.jp
  • P. Vajda (Czech Rep.) peter.vajda@savba.sk
  • P. Varga (Hungary) peter@seismology.hu
  • L.L.A. Vermeersen (NL) b.vermeersen@lr.tudelft.nl
  • D. Wolf (Germany) dasca@gfz-potsdam.de
  • P. Wu (Canada) ppwu@ucalgary.ca

Associate Members

  • E. W. Grafarend (Germany) grafarend@gis.uni-stuttgart.de
  • J. Hinderer (France) jhinderer@eost.u-strasbg.fr
  • L. E. Sjöberg (Sweden) sjoberg@geomatics.kth.se

IC-SG8 Towards cm-accurate Geoid – Theories, Computational Methods and Validation

Chair: Y. M. Wang (USA) 

Affiliation: Commission 2

Introduction

In today's satellite age, the ellipsoidal height can be deter-mined up to 2 cm-accuracy geometrically by the global positioning system (GPS). If geoid models reach the same accuracy, national or global vertical systems can be established in a quick and economical way with cm-accuracy everywhere. 

Geoid modelling has been based on Stokes and Molodensky's theories. In both theories, including the theories of gravity and topographic reductions which are fundamentally important for precise geoid computation, approximations and assumptions are made. The evalua-tion and verification of the effects of assumptions and approximations in the theories are urgently called for. Due to the massive effort on data collection that has improved our knowledge of the Earth's physical surface and its interior, fixed-boundary value problems become practical and useful. Theoretical and numerical studies along this line are not only important in practice, but also may be a fundamental change in physical geodesy. 

The working group aims at bringing together scientists concerned with all aspects of the diverse areas of geo-detically relevant theory and its applications. Its goal is to provide a framework consisting of theories and computa-tional methods to ensure that cm-accurate geoid is achievable. 

Objectives

Theoretical research related to precise geoid computations; studies of geodetic boundary values problems (free and fixed boundary value problems); development and refinement of gravity/topographic reduction theories; exploration and implementation of numerical methods of partial differential equations for Earth's gravity field determination (e.g., domain decomposition, spectral combination and others).

In more details, this includes: 

  • Studies of the effect of topographic density variations on the Earth's gravity field, especially the geoid.
  • Rigorous yet efficient calculation of the topographic effects, refinement of the topographic and gravity reductions.
  • Studies on harmonic downward continuations.
  • Non-linear effects of the geodetic boundary value problems on the geoid determinations.
  • Optimal combination of global gravity models with local gravity data.
  • Exploration of numerical methods in solving the geo-detic boundary value problems (domain decomposi-tion, finite elements, and others)
  • Studies on data requirements, data quality, distribution and sample rate, for a cm- accurate geoid.
  • Studies on the time variations of the geoid caused by geodynamics.
  • Studies on the interdisciplinary approach for marine geoid determination, e.g., research on realization of a global geoid consistent with the global mean sea surface observed by satellites.

Program of Activities

  • Organization of meetings and conferences.
  • Organizing WG meetings or sessions, in coincidence with a larger event, if the presence of working group members appears sufficiently large.
  • Email discussion and electronic exchange.
  • Launching a web page for dissemination of informa-tion, expressing aims, objectives, and discussions.
  • Monitoring and reporting activities of working group members and interested external individuals.

Membership

  • Y.M. Wang, USA (chair)
  • W. Featherstone, Australia
  • N. Kühtreiber, Austria
  • H. Moritz, Austria
  • M.G. Sideris, Canada
  • M. Véronneau, Canada
  • J. Huang, Canada
  • M. Santos, Canada
  • J.C. Li, China
  • D.B. Cao, China
  • W.B. Shen, China
  • F. Mao, China
  • Z. Martinec, Czech Republic
  • R. Forsberg, Denmark
  • O. Anderson, Denmark
  • H. Abd-Elmotaal, Egypt
  • H. Denker, Germany
  • B. Heck, Germany
  • W. Freeden, Germany
  • J. H. Kwon, Korea
  • L. Sjöberg, Sweden
  • D. Roman, USA
  • J. Saleh, USA
  • D. Smith (USA)

IC-SG3 Analysis of complex time series 

Chair: W. Kosek (Poland)

Objectives

The objective of a study group on "Analysis of complex time series" would be to investigate the diverse methodologies and approaches across the geodetic subdisciplines on time-series analysis. The study group membership combines the expertise in time series analysis of EOP, GPS-coordinates, sea level, superconducting gravi-metry, and so on. The ultimate goal would be a consoli-dation between such methodologies, or at least recom-mendations in that direction.

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