Difference between pages "IC SG3" and "IC SG5"

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==Configuration analysis of Earth oriented space techniques==
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<big>'''JSG 0.14: Fusion of multi-technique satellite geodetic data'''</big>
  
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Chair: ''F. Seitz (Germany)''
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Chair: ''Krsyzstof Sośnica (Poland)''<br>
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Affiliation: ''Comm. 3, 2, 1''
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Affiliation: ''All Commissions and GGOS''
  
 
__TOC__
 
__TOC__
  
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===Introduction===
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===Terms of Reference===
  
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Activities of the study group are focussed on modern methods of Earth observation from space. Today a multitude of simultaneously operating satellite systems with different objectives are available. They offer a broad spectrum of information on global and regional-scale processes within and/or between individual components of the Earth system in different temporal resolutions.
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Observations provided by space geodetic techniques deliver a global picture of the changing system Earth, in particular temporal changes of the Earth’s gravity field, irregularities in the Earth rotation and variations of station positions due to various geodynamical phenomena. Different techniques are characterized by different accuracy and different sensitivity to geodetic parameters, e.g., GNSS provides most accurate pole coordinates, but cannot provide the absolute information on UT1-UTC, and thus, must be integrated with VLBI or LLR data. GRACE observations provide state-of-the-art and most accurate information on temporal changes of the gravity field, but the temporal changes of the Earth’s oblateness or the geocentre motion can be better determined using SLR data. Therefore, a fusion of various space geodetic observations is an indispensable prerequisite for a reliable description of the varying system Earth.
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However, the space geodetic observations are typically not free of artifacts related to deficiencies in various models used in the data reduction process. GNSS satellite orbits are very sensitive to deficiencies in solar radiation pressure modeling affecting, e.g., the accuracy of GNSS-derived Earth rotation parameters and geocentre coordinates. Deficiencies in modeling of antenna phase center offsets, albedo and the antenna thrust limit the reliability of GNSS and DORIS-derived scale of the terrestrial reference frame, despite a good global coverage of GNSS receivers and DORIS beacons. VLBI solutions are affected by an inhomogeneous quality delivered by different stations and antenna deformations. SLR technique is affected by the Blue-Sky effect which is related to the weather dependency of laser observations and the station-dependent satellite signature effect due to multiple reflections from many retroreflectors. Moreover, un-modeled horizontal gradients of the troposphere delay in SLR analyzes also limit the quality of SLR solutions. Finally, GRACE data are very sensitive to aliasing with diurnal and semidiurnal tides, whereas GOCE and Swarm orbits show a worse quality around the geomagnetic equator due to deficiencies in ionosphere delay modeling.
  
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The general objective of this study group is the development of strategies how complementary and redundant information from heterogeneous observation types can be combined and analysed with respect to physical processes in the Earth system.
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Separation of real geophysical signals and artifacts in geodetic observations yield a very challenging objective. A fusion of different observational techniques of space geodesy may enhance our knowledge on systematic effects, improve the consistency between different observational techniques, and may help us to mitigate artifacts in the geodetic time series.
  
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Most of the measurement techniques are restricted to the observation of integral effects of a multitude of underlying geophysical processes. It shall be investigated in which way the combination of heterogeneous data sets allows for the separation of processes and the identification of individual contributors.
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The mitigation of artifacts using parameters derived by a fusion of different techniques of space geodesy should comprise three steps: 1) identification of an artifact through an analysis of geodetic parameters derived from multiple techniques; 2) delivering a way to model an artifact; 3) applying the developed model to standard solutions by the analysis centers.  
  
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In particular the studies span geometrical observation techniques (e.g. point positioning systems, imaging radar systems), gravimetrical observation techniques (e.g. GRACE, GOCE) and sensors which allow for the direct observation of individual physical processes (e.g., IceSat, SMOS).
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Improving the consistency level through mitigating artifacts in space geodetic observations will bring us closer to fulfilling the objectives of the Global Geodetic Observing System (GGOS), i.e., the 1-mm accuracy of positions and 0.1-mm/year accuracy of the velocity determination. Without a deep knowledge of systematic effects in satellite geodetic data and without a proper modeling thereof, the accomplishment of the GGOS goals will never be possible.  
  
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The combination of complementary and redundant observation types fosters and improves the understanding of the Earth system. This implies more reliable information on processes and interactions in the subsystems of the Earth which is especially necessary with regard to studies of global change.
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===Objectives===
  
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Among the most important steps are compilation and assessment of background information for individual systems and sensors (mode of operation, sensitivity, accuracy, deficiencies) as well as theoretical studies which (new) information on the Earth system can be gained from a combination of different observation methods.
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* Developing of data fusion methods based on geodetic data from different sources
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* Accuracy assessment and simulations of geodetic observations in order to fulfil GGOS’ goals
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* Study time series of geodetic parameters (geometry, gravity and rotation) and other derivative parameters (e.g., troposphere and ionosphere delays) determined using different techniques of space geodesy
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* Investigating biases and systematic effects in single techniques
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* Combination of satellite geodetic observations at the observation level and software synchronization
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* Investigating various methods of technique co-locations: through local ties, global ties, co-location in space
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* Identifying artifacts in time series of geodetic parameters using e.g., spatial, temporal, and spectral analyzes
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* Elaborating methods aimed at mitigating systematic effects and artifacts
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* Determination of the statistical significance levels of the results obtained by techniques using different methods and algorithms
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* Comparison of different methods in order to point out their advantages and disadvantages
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* Recommendations for analysis working groups and conventions
  
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===Objectives===
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===Planned Activities===
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* Preparing a web page with information concerning integration and consistency of satellite geodetic techniques and their integration with special emphasis on exchange of ideas, providing and updating bibliographic list of references of research results and relevant publications from different disciplines.
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* Working meetings at the international symposia and presentation of research results at the appropriate sessions.
  
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* which processes in the Earth system are insufficiently known and which parameters are imprecisely determined?
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===Members===
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* can the understanding of individual processes be improved by common analysis of different observations types?
 
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* which are the target parameters and how are the connections with other variables?
 
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* which sensors are available and sensitive for the target parameters?
 
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* which sensors can be used to reduce unwanted signals?
 
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* which are the accuracies, temporal and spatial resolutions of the different data sets and which regions and time spans are covered?
 
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* are the data publicly available or is their access restricted?
 
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* which pre-processing steps are neccessary in order to extract the proper information from the raw observtion data?
 
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* have the data already been pre-processed? Which methods, models and conventions have been applied? Are there possible error sources or inconsistencies?
 
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* which methods can be applied in order to enhance the information content (e.g. filters)?
 
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* how can the heterogeneous observation types can be combined expediently?
 
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* how do the observation equations look like?
 
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* which methods for parameter estimation can be applied? How can linear dependencies between parameters and rank deficiency problems be solved?
 
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* how can balance equations be regarded in the combination process (e.g. mass and energy balance)?
 
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* are ther additional information (models and terrestrial data) which can/must be considered?
 
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* which of the desired parameters can be assessed with the available observation techniques?
 
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* which further parameters are desired and how could appropriate missions for the future look like?
 
  
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The research activities shall be coordinated between the participating scientists and shall be conducted in interdisciplinary collaboration. At all times the group is open for new contacts and members in order to embed the activities in a wide context.
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'' '''Krzysztof Sośnica (Poland), chair''' <br /> Toshimichi Otsubo (Japan) <br /> Daniela Thaller (Germany) <br /> Mathis Blossfeld (Germany) <br /> Andrea Maier (Switzerland) <br /> Claudia Flohrer (Germany) <br /> Agnieszka Wnek (Poland) <br /> Sara Bruni (Italy) <br /> Karina Wilgan (Poland) <br />''

Latest revision as of 12:20, 24 April 2016

JSG 0.14: Fusion of multi-technique satellite geodetic data

Chair: Krsyzstof Sośnica (Poland)
Affiliation: All Commissions and GGOS

Terms of Reference

Observations provided by space geodetic techniques deliver a global picture of the changing system Earth, in particular temporal changes of the Earth’s gravity field, irregularities in the Earth rotation and variations of station positions due to various geodynamical phenomena. Different techniques are characterized by different accuracy and different sensitivity to geodetic parameters, e.g., GNSS provides most accurate pole coordinates, but cannot provide the absolute information on UT1-UTC, and thus, must be integrated with VLBI or LLR data. GRACE observations provide state-of-the-art and most accurate information on temporal changes of the gravity field, but the temporal changes of the Earth’s oblateness or the geocentre motion can be better determined using SLR data. Therefore, a fusion of various space geodetic observations is an indispensable prerequisite for a reliable description of the varying system Earth.

However, the space geodetic observations are typically not free of artifacts related to deficiencies in various models used in the data reduction process. GNSS satellite orbits are very sensitive to deficiencies in solar radiation pressure modeling affecting, e.g., the accuracy of GNSS-derived Earth rotation parameters and geocentre coordinates. Deficiencies in modeling of antenna phase center offsets, albedo and the antenna thrust limit the reliability of GNSS and DORIS-derived scale of the terrestrial reference frame, despite a good global coverage of GNSS receivers and DORIS beacons. VLBI solutions are affected by an inhomogeneous quality delivered by different stations and antenna deformations. SLR technique is affected by the Blue-Sky effect which is related to the weather dependency of laser observations and the station-dependent satellite signature effect due to multiple reflections from many retroreflectors. Moreover, un-modeled horizontal gradients of the troposphere delay in SLR analyzes also limit the quality of SLR solutions. Finally, GRACE data are very sensitive to aliasing with diurnal and semidiurnal tides, whereas GOCE and Swarm orbits show a worse quality around the geomagnetic equator due to deficiencies in ionosphere delay modeling.

Separation of real geophysical signals and artifacts in geodetic observations yield a very challenging objective. A fusion of different observational techniques of space geodesy may enhance our knowledge on systematic effects, improve the consistency between different observational techniques, and may help us to mitigate artifacts in the geodetic time series.

The mitigation of artifacts using parameters derived by a fusion of different techniques of space geodesy should comprise three steps: 1) identification of an artifact through an analysis of geodetic parameters derived from multiple techniques; 2) delivering a way to model an artifact; 3) applying the developed model to standard solutions by the analysis centers.

Improving the consistency level through mitigating artifacts in space geodetic observations will bring us closer to fulfilling the objectives of the Global Geodetic Observing System (GGOS), i.e., the 1-mm accuracy of positions and 0.1-mm/year accuracy of the velocity determination. Without a deep knowledge of systematic effects in satellite geodetic data and without a proper modeling thereof, the accomplishment of the GGOS goals will never be possible.

Objectives

  • Developing of data fusion methods based on geodetic data from different sources
  • Accuracy assessment and simulations of geodetic observations in order to fulfil GGOS’ goals
  • Study time series of geodetic parameters (geometry, gravity and rotation) and other derivative parameters (e.g., troposphere and ionosphere delays) determined using different techniques of space geodesy
  • Investigating biases and systematic effects in single techniques
  • Combination of satellite geodetic observations at the observation level and software synchronization
  • Investigating various methods of technique co-locations: through local ties, global ties, co-location in space
  • Identifying artifacts in time series of geodetic parameters using e.g., spatial, temporal, and spectral analyzes
  • Elaborating methods aimed at mitigating systematic effects and artifacts
  • Determination of the statistical significance levels of the results obtained by techniques using different methods and algorithms
  • Comparison of different methods in order to point out their advantages and disadvantages
  • Recommendations for analysis working groups and conventions

Planned Activities

  • Preparing a web page with information concerning integration and consistency of satellite geodetic techniques and their integration with special emphasis on exchange of ideas, providing and updating bibliographic list of references of research results and relevant publications from different disciplines.
  • Working meetings at the international symposia and presentation of research results at the appropriate sessions.

Members

Krzysztof Sośnica (Poland), chair
Toshimichi Otsubo (Japan)
Daniela Thaller (Germany)
Mathis Blossfeld (Germany)
Andrea Maier (Switzerland)
Claudia Flohrer (Germany)
Agnieszka Wnek (Poland)
Sara Bruni (Italy)
Karina Wilgan (Poland)

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