Difference between pages "IC SG1" and "IC SG2"

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<big>'''Theory, implementation and quality assessment of geodetic reference frames'''</big>
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<big>'''JSG 0.2: Gravity field modelling in support of world height system realization'''</big>
  
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Chair: ''A. Dermanis (Greece)''<br>
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Chair:''P. Novák (Czech Republic)''<br>
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Affiliation:''Comm. 1, IERS''
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Affiliation:''Comm. 2, 1 and GGOS''
  
 
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__TOC__
 
===Introduction===
 
===Introduction===
  
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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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Description of the Earth’s gravity field still remains a major research topic in geodesy. The main goal is to pro-vide reliable global models covering all spatially-temporal frequencies of its scalar parameterization through the gravity potential. Detailed and accurate gravity field models are required for proper positioning and orientation of geodetic sensors (data geo-referencing). Geometric properties of the gravity field are then studied including those of its equipotential surfaces and their respective sur-face normals, since they play a fundamental role in defini-tion and realization of geodetic reference systems. Gravity field models will be applied for definition and realization of a vertical reference system (currently under construc-tion) that will support studies of the Earth system.
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This study group is an entity of the Inter-Commission Committee on Theory. It is affiliated to Commissions 1 (Reference Frames) and 2 (Gravity Field); its close co-operation with GGOS Theme 1 “Unified Global Height System” is anticipated. It aims at bringing together scien-tists concerned namely with theoretical aspects in the areas of interest specified below.
  
 
===Objectives===
 
===Objectives===
  
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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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* Considering different types and large amounts of gravity-related data available today, large variety of gravity field models and the ongoing IAG project of realizing a world height system (WHS), this study group shall focuses on theoretical aspects related to the following (non-exhaustive to WHS) list of problems:
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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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* To study available gravity field models in terms of their available resolution, accuracy and stability for the pur-pose of WHS realization.
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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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* To define a role of a conventional model of the Earth’s gravity field (EGM) to be used for WHS realization in-cluding its scale parameters.
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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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* To study relations between an adopted conventional EGM and parameters of a geocentric reference ellipsoid of revolution approximating a time invariant equipoten-tial surface of the adopted EGM aligned to reduced observables of mean sea level.
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* Statistical aspects of reference frames, introduction and assessment of appropriate quality measures.
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* To study theoretical aspects of various methods proposed for WHS definition and realization including investiga-tions on tidal system effects.
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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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To investigate combination of heterogeneous gravity field observables by using spatial inversion, spherical radial functions, collocation, wavelets, etc. and by taking into account their sampling geometry, spectral and stochastic properties.
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* To investigate methods of gravity field modelling based on combination of global gravitational models, ground and airborne gravity, GNSS/levelling height differences, altimetry data, deflections of the vertical, etc.
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* To study stable, accurate and efficient methods for con-tinuation of gravity field parameters including space-borne observables of type GRACE and GOCE.
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* To advance theory and methods for solving various initial and boundary value problems (I/BVP) in geodesy.
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* To study methods for gravity potential estimation based on its measured directional derivatives (gravity, gravity gradients) by exploiting advantages of simultaneous con-tinuation and inversion of observations.
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* To investigate requirements for gravity data (stochastic properties, spatially-temporal sampling, spectral content etc.) in terms of their specific geodetic applications.
  
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===Program of Activities===
  
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===Program of activities===
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Active participation at major geodetic conferences and meetings.
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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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Organizing a session at the Hotine-Marussi Symposium 2013.
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* Working meetings at international symposia and presentation of research results in appropriate sessions.
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Co-operation with affiliated IAG Commissions and GGOS.
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* Organization of workshops dedicated mainly to problem identification and motivation of relevant scientific research.
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Electronic exchange of ideas and thoughts through a SG web page.
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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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Monitoring activities of SG members and external individuals related to SG.
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Compiling bibliography in the area of SG interest.
  
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===Members===
  
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===Membership===
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'' '''Pavel Novák (Czech Republic), chair'''<br />Hussein Abd-Elmotaal (Egypt)<br />Robert Čunderlík (Slovakia)<br />Heiner Denker (Germany)<br />Will Featherstone (Australia)<br />René Forsberg (Denmark)<br />Bernhard Heck (Germany)<br />Jianliang Huang (Canada)<br />
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Christopher Jekeli (USA)<br />Dan Roman (USA)<br />Fernando Sansò (Italy)<br />Michael G Sideris (Canada)<br />Lars Sjöberg (Sweden)<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 />''
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Robert Tenzer (New Zealand)<br />Yan-Ming Wang (USA)<br />''

Revision as of 10:59, 29 June 2012

JSG 0.2: Gravity field modelling in support of world height system realization

Chair:P. Novák (Czech Republic)
Affiliation:Comm. 2, 1 and GGOS

Introduction

Description of the Earth’s gravity field still remains a major research topic in geodesy. The main goal is to pro-vide reliable global models covering all spatially-temporal frequencies of its scalar parameterization through the gravity potential. Detailed and accurate gravity field models are required for proper positioning and orientation of geodetic sensors (data geo-referencing). Geometric properties of the gravity field are then studied including those of its equipotential surfaces and their respective sur-face normals, since they play a fundamental role in defini-tion and realization of geodetic reference systems. Gravity field models will be applied for definition and realization of a vertical reference system (currently under construc-tion) that will support studies of the Earth system. This study group is an entity of the Inter-Commission Committee on Theory. It is affiliated to Commissions 1 (Reference Frames) and 2 (Gravity Field); its close co-operation with GGOS Theme 1 “Unified Global Height System” is anticipated. It aims at bringing together scien-tists concerned namely with theoretical aspects in the areas of interest specified below.

Objectives

  • Considering different types and large amounts of gravity-related data available today, large variety of gravity field models and the ongoing IAG project of realizing a world height system (WHS), this study group shall focuses on theoretical aspects related to the following (non-exhaustive to WHS) list of problems:
  • To study available gravity field models in terms of their available resolution, accuracy and stability for the pur-pose of WHS realization.
  • To define a role of a conventional model of the Earth’s gravity field (EGM) to be used for WHS realization in-cluding its scale parameters.
  • To study relations between an adopted conventional EGM and parameters of a geocentric reference ellipsoid of revolution approximating a time invariant equipoten-tial surface of the adopted EGM aligned to reduced observables of mean sea level.
  • To study theoretical aspects of various methods proposed for WHS definition and realization including investiga-tions on tidal system effects.

To investigate combination of heterogeneous gravity field observables by using spatial inversion, spherical radial functions, collocation, wavelets, etc. and by taking into account their sampling geometry, spectral and stochastic properties.

  • To investigate methods of gravity field modelling based on combination of global gravitational models, ground and airborne gravity, GNSS/levelling height differences, altimetry data, deflections of the vertical, etc.
  • To study stable, accurate and efficient methods for con-tinuation of gravity field parameters including space-borne observables of type GRACE and GOCE.
  • To advance theory and methods for solving various initial and boundary value problems (I/BVP) in geodesy.
  • To study methods for gravity potential estimation based on its measured directional derivatives (gravity, gravity gradients) by exploiting advantages of simultaneous con-tinuation and inversion of observations.
  • To investigate requirements for gravity data (stochastic properties, spatially-temporal sampling, spectral content etc.) in terms of their specific geodetic applications.

Program of Activities

Active participation at major geodetic conferences and meetings. Organizing a session at the Hotine-Marussi Symposium 2013. Co-operation with affiliated IAG Commissions and GGOS. Electronic exchange of ideas and thoughts through a SG web page. Monitoring activities of SG members and external individuals related to SG. Compiling bibliography in the area of SG interest.

Members

Pavel Novák (Czech Republic), chair
Hussein Abd-Elmotaal (Egypt)
Robert Čunderlík (Slovakia)
Heiner Denker (Germany)
Will Featherstone (Australia)
René Forsberg (Denmark)
Bernhard Heck (Germany)
Jianliang Huang (Canada)
 Christopher Jekeli (USA)
Dan Roman (USA)
Fernando Sansò (Italy)
Michael G Sideris (Canada)
Lars Sjöberg (Sweden)
Robert Tenzer (New Zealand)
Yan-Ming Wang (USA)

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