Difference between revisions of "IC SG1"

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<big>'''JSG 0.1: Application of time-series analysis in geodesy'''</big>
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==IC-SG1: Theory, implementation and quality assessment of geodetic reference frames==
  
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Chair: ''W. Kosek (Poland)''<br>
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__TOC__
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Affiliation:''GGOS, all commissions''
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{|
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| Chair:
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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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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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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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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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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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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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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.
  
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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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===Objectives===
  
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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.
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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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===Objectives===
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In more details, this includes:
  
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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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* Studies of the effect of topographic density variations on the Earth's gravity field, especially the geoid.
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* The evaluation of appropriate covariance matrices corresponding to the time series by applying the law of error propagation, including weighting schemes, regularization, etc.
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* Rigorous yet efficient calculation of the topographic effects, refinement of the topographic and gravity reductions.
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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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* Studies on harmonic downward continuations.
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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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* Non-linear effects of the geodetic boundary value problems on the geoid determinations.
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* Developing and implementing the algorithms – aiming to seek and utilize spatio-temporal correlations – for geodetic time series modelling and prediction.
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* Optimal combination of global gravity models with local gravity data.
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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 strategies employed for numerous geodetic 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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* Developing combination strategies for time- and space-dependent data obtained from different geodetic observations.
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* Studies on data requirements, data quality, distribution and sample rate, for a cm- accurate geoid.
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* Developing separation techniques for integral measurements in individual contributions.
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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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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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Participating in working meetings at the international sym-posia and presenting scientific results at the appropriate sessions.
 
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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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===Members===
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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.
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===Membership===
  
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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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'' '''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 />''

Revision as of 13:39, 22 April 2008

IC-SG1: Theory, implementation and quality assessment of geodetic reference frames

Chair: Y.M. Wang (USA)
Affiliation: Comm. 2

Introduction

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.

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.

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

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 geodetic boundary value problems (domain decomposition, 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 information, 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

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