Difference between revisions of "IC SG1"

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==IC-SG1: Theory, implementation and quality assessment of geodetic reference frames==
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<big>'''Theory, implementation and quality assessment of geodetic reference frames'''</big>
  
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Chair: ''A. Dermanis (Greece)''<br>
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| Chair:
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Affiliation:''Comm. 1, IERS''
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! ''Y.M. Wang (USA)''
 
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|-
 
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| Affiliation:
 
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! ''Comm. 2''
 
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|}
 
  
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__TOC__
 
===Introduction===
 
===Introduction===
  
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In today's satellite age, the ellipsoidal height can be determined 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.
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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.  
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Geoid modeling 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 evaluation 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.
 
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The working group aims at bringing together scientists concerned with all aspects of the diverse areas of geodetically relevant theory and its applications. Its goal is to provide a framework consisting of theories and computational methods to ensure that cm-accurate geoid is achievable.
 
  
 
===Objectives===
 
===Objectives===
  
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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).
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* 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.
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* Understanding the relation between such systems and reference systems implicitly introduced in theories of earth rotation and deformation.
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In more details, this includes:
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* 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.
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* 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.  
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* Statistical aspects of reference frames, introduction and assessment of appropriate quality measures.
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* Problems of mathematical compatibility within current celestial-to-terrestrial datum transformations and proposal of new conventions which are data-based and theoretically compatible.
  
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* Studies of the effect of topographic density variations on the Earth's gravity field, especially the geoid.
 
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* Rigorous yet efficient calculation of the topographic effects, refinement of the topographic and gravity reductions.
 
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* Studies on harmonic downward continuations.
 
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* Non-linear effects of the geodetic boundary value problems on the geoid determinations.
 
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* Optimal combination of global gravity models with local gravity data.
 
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* Exploration of numerical methods in solving the geodetic boundary value problems (domain decomposition, finite elements, and others)
 
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* Studies on data requirements, data quality, distribution and sample rate, for a cm- accurate geoid.
 
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* Studies on the time variations of the geoid caused by geodynamics.
 
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* 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===
 
===Program of activities===
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* Launching of a web-page for dissemination of information, presentation, communication, outreach purposes, and providing a bibliography.
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* Working meetings at international symposia and presentation of research results in appropriate sessions.
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* Organization of workshops dedicated mainly to problem identification and motivation of relevant scientific research.
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* A special issue of the Journal of Geodesy on reference frames with papers from working group workshops and invited review papers.
  
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* Organization of meetings and conferences.
 
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* Organizing WG meetings or sessions, in coincidence with a larger event, if the presence of working group members appears sufficiently large.
 
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* Email discussion and electronic exchange.
 
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* Launching a web page for dissemination of information, expressing aims, objectives, and discussions.
 
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* Monitoring and reporting activities of working group members and interested external individuals.
 
  
 
===Membership===
 
===Membership===
  
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'' '''Y.M. Wang, (USA, chair)'''<br /> W. Featherstone, Australia<br /> N. Kühtreiber, Austria<br /> H. Moritz, Austria<br /> M.G. Sideris, Canada<br /> M. Véronneau, Canada<br /> J. Huang, Canada<br /> M. Santos, Canada<br /> J.C. Li, China<br /> D.B. Cao, China<br /> W.B. Shen, China<br /> F. Mao, China<br /> Z. Martinec, Czech Republic<br /> R. Forsberg, Denmark<br /> O. Anderson, Denmark<br /> H. Abd-Elmotaal, Egypt<br /> H. Denker, Germany<br /> B. Heck, Germany<br /> W. Freeden, Germany<br /> J. H. Kwon, Korea<br /> L. Sjöberg, Sweden<br /> D. Roman, USA<br /> J. Saleh, USA<br /> D. Smith USA<br />''
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'' '''Athanasios Dermanis, (Greece, Chair)'''<br /> Zuheir Altamimi (France) <br /> Hermann Drewes (Germany) <br /> Fernando Sansò (Italy) <br /> Claude Boucher (France) <br /> Gerard Petit (France) <br /> Xavier Collilieux (France) <br /> Axel Nothnagel (Germany) <br /> Erricos Pavlis (USA) <br /> Jim Ray (USA) <br /> Frank Lemoine (USA) <br /> Geoff Blewitt (USA) <br /> Ludovico Biagi (Italy) <br /> Thomas Herring (U.S.A.) <br /> Pascal Willis (France) <br />''

Revision as of 14:27, 15 February 2010

Theory, implementation and quality assessment of geodetic reference frames

Chair: A. Dermanis (Greece)
Affiliation:Comm. 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 web-page for dissemination of information, presentation, communication, outreach purposes, and providing a bibliography.
  • Working meetings at international symposia and presentation 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, (Greece, Chair)
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)
Ludovico Biagi (Italy)
Thomas Herring (U.S.A.)
Pascal Willis (France)

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