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

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<big>'''JSG 0.1: Application of time-series analysis in geodesy'''</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: ''W. Kosek (Poland)''<br>
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Chair:''P. Novák (Czech Republic)''<br>
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Affiliation:''GGOS, all commissions''
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Affiliation:''Comm. 2, 1 and GGOS''
  
 
__TOC__
 
__TOC__
 
===Introduction===
 
===Introduction===
  
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Observations provided by modern space geodetic techniques (geometric and gravimetric) deliver a global picture of dynamics of the Earth. Such observations are usually represented as time series which describe (1) changes of surface geometry of the Earth due to horizontal and vertical deformations of the land, ocean and cryosphere, (2) fluctuations in the orientation of the Earth divided into precession, nutation, polar motion and spin rate, and (3) variations of the Earth’s gravitational field and the centre of mass of the Earth. The vision and goal of GGOS is to understand the dynamic Earth’s system by quantifying our planet’s changes in space and time and integrate all observations and elements of the Earth’s system into one unique physical and mathematical model. To meet the GGOS requirements, all temporal variations of the Earth’s dynamics – which represent the total and hence integral effect of mass exchange between all elements of Earth’s system including atmosphere, ocean and hydrology – should be properly described by time series methods.
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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.
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Various time series methods have been applied to analyze such geodetic and related geophysical time series in order to better understand the relation between all elements of the Earth’s system. The interactions between different components of the Earth’s system are very complex, thus the nature of the considered signals in the geodetic time series is mostly wideband, irregular and non-stationary. Therefore, the application of time frequency analysis methods based on wavelet coefficients – e.g. time-frequency cross-spectra, coherence and semblance – is necessary to reliably detect the features of the temporal or spatial variability of signals included in various geodetic data, and other associated geophysical data.
 
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Geodetic time series may include, for instance, temporal variations of site positions, tropospheric delay, ionospheric total electron content, masses in specific water storage compartments or estimated orbit parameters as well as surface data including gravity field, sea level and ionosphere maps. The main problems to be scrutinized concern the estimation of deterministic (including trend and periodic variations) and stochastic (non-periodic variations and random fluctuations) components of the time series along with the application of the appropriate digital filters for extracting specific components with a chosen frequency bandwidth. The application of semblance filtering enables to compute the common signals, understood in frame of the time-frequency approach, which are embedded in various geodetic/geophysical time series.
 
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Numerous methods of time series analysis may be employed for processing raw data from various geodetic measurements in order to promote the quality level of signal enhancement. The issue of improvement of the edge effects in time series analysis may also be considered. Indeed, they may either affect the reliability of long-range tendency (trends) estimated from data or the real-time processing and prediction.
 
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The development of combination strategies for time- and space-dependent data processing, including multi-mission sensor data, is also very important. Numerous observation techniques, providing data with different spatial and temporal resolutions and scales, can be combined to compute the most reliable geodetic products. It is now known that incorporating space variables in the process of geodetic time series modelling and prediction can lead to a significant improvement of the prediction performance. Usually multi-sensor data comprises a large number of individual effects, e.g., oceanic, atmospheric and hydrological contributions. In Earth system analysis one key point at present and in the future will be the development of separation techniques. In this context principal component analysis and related techniques can be applied.
 
  
 
===Objectives===
 
===Objectives===
  
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* To study geodetic time series and their geophysical causes in different frequency bands using time series analysis methods, mainly for better understanding of their causes and prediction improvement.
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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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* The evaluation of appropriate covariance matrices corre-sponding to the time series by applying the law of error propagation, including weighting schemes, regulariza-tion, etc.
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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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* Determining statistical significance levels of the results obtained by different time series analysis methods and algorithms applied to geodetic time series.
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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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* The comparison of different time series analysis methods and their recommendation, with a particular emphasis put on solving problems concerning specific geodetic data.
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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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* Developing and implementing the algorithms – aiming to seek and utilize spatio-temporal correlations – for geo-detic time series modelling and prediction.
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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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* Better understanding of how large-scale environmental processes, such as for instance oceanic and atmospheric oscillations and climate change, impact modelling strate-gies employed for numerous geodetic data.
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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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* Developing combination strategies for time- and space-dependent data obtained from different geodetic observa-tions.
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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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* Developing separation techniques for integral measure-ments in individual contributions.
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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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Updating the webpage, so that the information on time series analysis and its application in geodesy (including relevant multidisciplinary publications and the unification of terminology applied in time series analysis) will be available.
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Organizing a session at the Hotine-Marussi Symposium 2013.
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Participating in working meetings at the international sym-posia and presenting scientific results at the appropriate sessions.
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Co-operation with affiliated IAG Commissions and GGOS.
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Collaboration with other working groups dealing with geo-detic time-series e.g. Cost ES0701 Improved constraints on models of GIA or the Climate Change Working Group.
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Electronic exchange of ideas and thoughts through a SG web page.
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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.
  
 
===Members===
 
===Members===
  
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'' '''W. Kosek (Poland), chair'''<br /> R. Abarca del Rio (Chile)<br /> O. Akyilmaz (Turkey)<br /> J. Böhm (Austria)<br /> L. Fernandez (Argentina)<br /> R. Gross (USA)<br /> M. Kalarus (Poland)<br /> M. O. Karslioglu (Turkey)<br /> H. Neuner (Germany)<br /> T. Niedzielski (Poland)<br /> S. Petrov (Russia)<br /> W. Popinski (Poland)<br /> M. Schmidt (Germany)<br /> M. van Camp (Belgium)<br /> O. de Viron (France)<br /> J. Vondrák (Czech Republic)<br /> D. Zheng (China)<br /> Y. Zhou (China)<br />''
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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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Robert Tenzer (New Zealand)<br>Yan-Ming Wang (USA)<br>''

Revision as of 10:58, 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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