IC SG5

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)