Difference between revisions of "IC SG9"

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<big>'''Application of time-series analysis in geodesy'''</big>
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<big>'''JSG 0.9: Future developments of ITRF models and their geophysical interpretation'''</big>
  
Chair: ''W. Kosek (Poland)''<br>
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Chair: ''A. Dermanis (Greece)''<br>
Affiliation:''Comm. 1, 2, 3, 4''
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Affiliation:''Comm. 1 and IERS''
  
 
__TOC__
 
__TOC__
===Introduction===
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===Terms of Reference===
  
Observations of the new space geodetic techniques (geometric and gravimetric) deliver a global picture of dynamics of the Earth usually represented in the form of time series which describe 1) changes of the surface geometry of the Earth due to horizontal and vertical deformations of the land surface, variations of the ocean surface and ice covers, 2) the fluctuations in the orientation of the Earth divided into precession, nutation, polar motion and spin rate, and, 3) the variations of the Earth’s gravitational field as well as the variations of the centre of mass of the Earth. Geometry, Earth rotation and the gravity field are the three components of the Global Geodetic Observing System (GGOS). The vision of GGOS is to integrate all observations and elements of the Earth’s system into one unique physical and mathematical model. However, the temporal variations of Earth rotation and gravity/geoid represent the total, integral effect of all mass exchange between all elements of Earth’s system including atmosphere, ocean and hydrology.
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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.
  
Different time series analysis methods are applied to analyze all these geodetic time series for better understanding of the relation between all elements of the Earth’s system as well as their geophysical causes. The interactions between different components of the Earth’s system are very complex so the nature of considered signals in the geodetic time series is mostly wideband, irregular and non-stationary. Thus, it is necessary to apply time frequency analysis methods in order to analyze these time series in different frequency bands as well as to explain their relations to geophysical processes e.g. by computing time frequency coherence between Earth’s rotation or the gravity field data and data representing the mass exchange between the atmosphere, ocean and hydrology. The techniques of time frequency spectrum and coherence may be developed further to display reliably the features of the temporal or spatial variability of signals existing in various geodetic data, as well as in other data sources.
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The remaining residual signal in coordinate variations is dominated by an almost periodic term with varying amplitude and phase, especially in the height component. The inclusion of additional terms in the ITRF model is an intricate problem that deserves further research and careful planning. It is also important to understand the nature of these coordinate variations in order to adopt models that are meaningful from the geophysical point of view and not a simple fit to the observed data. Since geophysical processes causing coordinate variations also cause variations in the gravity field, it is worthwhile to investigate the possibility of incorporating result results from space gravity missions in ITRF modelling. The working group is primarily aiming in identification of new ITRF models, investigation of their performance and motivation of relevant scientific research.
  
Geodetic time series may include for example variations of site positions, tropospheric delay, ionospheric total electron content, temporal variations of estimated orbit parameters.  Time series analysis methods can be also applied to analyze data on the surface including maps of the gravity field, sea level and ionosphere as well as temporal variations of such surface data. The main problems to deal with concern the estimation of deterministic (including trend and periodic variations) and stochastic (non-periodic variations and random changes) components of the geodetic time series as well as the application of digital filters for extracting specific components with a chosen frequency bandwidth. 
 
 
The multiple methods of time series analysis may be encouraged to be applied to the preprocessing of raw data from various geodetic measurements in order to promote the quality level of enhancement of signals existing in the raw data. The topic on the improvement of the edge effects in time series analysis may also be considered, since they may affect the reliability of long-range tendency (trends) estimated from data series as well as the real-time data processing and prediction.
 
 
For coping with small geodetic samples one can apply simulation-based methods and if the data are sparse, Monte-Carlo simulation or bootstrap technique may be useful.
 
 
Understanding the nature of geodetic time series is very important from the point of view of appropriate spectral analysis as well as application of filtering and prediction methods.
 
 
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===Objectives===
 
===Objectives===
  
Study of the nature of geodetic time series to choose optimum time series analysis methods  for filtering, spectral analysis, time frequency analysis and prediction.
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* Geophysical interpretation of non-linear coordinate variations and sevelopement of relevant models.
 
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* Extension of ITRF beyond the current linear (constant velocity) model, treatment of periodic and discontinuous station coordinate time series and establishment of proper procedures for estimation of extended ITRF parameters and quality assessment of the obtained results.
Study of Earth rotation and gravity field variations and their geophysical causes in different frequency bands.
 
 
 
Evaluation of appropriate covariance matrices for the time series by applying the law of error propagation to the original measurements, including weighting schemes, regularization, etc.
 
 
 
Determination of the statistical significance levels of the results obtained by different time series analysis methods and algorithms applied to geodetic time series.
 
 
 
Comparison of different time series analysis methods in order to point out their advantages and disadvantages.
 
 
 
Recommendations of different time series analysis methods for solving problems concerning specific geodetic time series.
 
  
 
===Program of activities===
 
===Program of activities===
  
Launching of a web page with information concerning time series analysis and it application to geodetic time series with special emphasis on exchange of ideas, providing and updating bibliographic list of references of research results and relevant publications from different disciplines as well as unification of terminology applied in time series analysis.  
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* Launching of a web-page for dissemination of informa-tion, presentation, communication, outreach purposes, and providing a bibliography.
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* Working meetings at international symposia and pre-sentation 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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* Organization of a second IAG School on Reference Frames.
  
Working meetings at the international symposia and presentation of research results at the appropriate sessions.
 
  
 
===Membership===
 
===Membership===
  
'' '''Wieslaw Kosek, Poland, chair'''<br /> Michael Schmidt, Germany<br /> Jan Vondrák, Czech Republic<br /> Waldemar Popinski, Poland<br /> Tomasz Niedzielski, Poland<br />Johannes Boehm, Germany<br />Rudolf Widmer-Schnidring, Germany<br />Dawei Zheng, China<br />Yonghong Zhou, China<br />Mahmut O. Karslioglu, Turkey<br />Orhan Akyilmaz, Turkey <br />''
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'' '''A. Dermanis (Greece), chair'''<br /> Z. Altamimi (France)<br /> X. Collilieux (France)<br /> H. Drewes (Germany)<br /> F. Sansò (Italy)<br />T. van Dam (Luxembourg)<br/>''

Revision as of 10:55, 2 July 2012

JSG 0.9: Future developments of ITRF models and their geophysical interpretation

Chair: A. Dermanis (Greece)
Affiliation:Comm. 1 and IERS

Terms of Reference

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 remaining residual signal in coordinate variations is dominated by an almost periodic term with varying amplitude and phase, especially in the height component. The inclusion of additional terms in the ITRF model is an intricate problem that deserves further research and careful planning. It is also important to understand the nature of these coordinate variations in order to adopt models that are meaningful from the geophysical point of view and not a simple fit to the observed data. Since geophysical processes causing coordinate variations also cause variations in the gravity field, it is worthwhile to investigate the possibility of incorporating result results from space gravity missions in ITRF modelling. The working group is primarily aiming in identification of new ITRF models, investigation of their performance and motivation of relevant scientific research.

Objectives

  • Geophysical interpretation of non-linear coordinate variations and sevelopement of relevant models.
  • Extension of ITRF beyond the current linear (constant velocity) model, treatment of periodic and discontinuous station coordinate time series and establishment of proper procedures for estimation of extended ITRF parameters and quality assessment of the obtained results.

Program of activities

  • Launching of a web-page for dissemination of informa-tion, 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.
  • Organization of a second IAG School on Reference Frames.


Membership

A. Dermanis (Greece), chair
Z. Altamimi (France)
X. Collilieux (France)
H. Drewes (Germany)
F. Sansò (Italy)
T. van Dam (Luxembourg)