Joint Working Groups
Working Group on Site Survey and Co-location
Joint with the IERS
Chair: Sten Bergstrand (Sweden)
Co-Chair: J. Dawson (Australia)
Link to the WG website at the IERS
Terms of Reference
The combination of space geodetic solutions is critically reliant on the availability of local tie vectors, which are the relative positions of the reference points of co-located space geodetic instruments determined by some survey technique. Tie vectors enter the combination of space geodetic solutions effectively as a fifth technique and are not only necessary for rigorous terrestrial reference frame realization but also serve to highlight the presence of technique- and/or site-specific biases.
With the ultimate objective of improving the accuracy of tie vectors as well as the consistency of space geodetic solutions, the Working Group (WG) will provide an authoritative source of surveying methodology advice, promote technical discussion, provide a forum for the evaluation of existing and new procedures and analysis strategies, and support the exchange of relevant information across GGOS and between the IAG technique services. Currently, dedicated points of contact (POC) have been established with IDS, IGS, ILRS and IVS. The WG will also support new survey activities with advice and advocate for re-survey where necessary.
Goals and objectives
Research:
- Revise existing local tie procedures
- Revise existing tie vector estimation processes
- Develop and define new methods
Coordination:
- Liaise with IERS combination centres
- Liaise with IAG technique services
- Direct research towards the investigation of technique specific systematic effects
Outreach:
- Remotely support local tie operations and tie vector estimation
- Spread the know-how
- Set guidelines
Members
- Sten Bergstrand (Sweden), Chair
- John Dawson (Australia), Vice-chair
- Rüdiger Haas (Sweden)
- Jerome Saunier (France)
- Ralf Schmid (Germany)
- Erricos C. Pavlis (USA)
- Jim Long (USA)
Modelling Environmental Loading Effects for Reference Frame Realizations
Joint with the IERS
Chair: Tonie van Dam (Luxembourg)
Vice-Chair: Anthony Mémin (Australia)
Terms of Reference
The accuracy and precision of current space geodetic techniques are such that displacements due to non-tidal surface mass loading are measurable. Many scientific studies have already considered atmospheric loading corrections at the observation level. The modeling of other non-tidal loading effects have been also investigated by various authors. In parallel, a posteriori corrections have been shown to slightly decrease the variance factor of a Terrestrial Reference Frame (TRF) multi-technique combination but the improvement at some sites was also counterbalanced by degradation at others.
There still exist open questions regarding the application of loading corrections for the generation of operational geodetic products, either a priori or a posteriori: accuracy of the models in all frequency bands - sub-daily band is the most important for a priori corrections -, too few studies regarding available loading model agreement have been carried out, proper mass conservation of all contributions and degree 0 of each contribution, methods that should be use for interpolating the loading displacements, required model resolution, reference loads that are or should be used for geodetic products, contribution of ice melting at high latitude which is not modeled in current continental water loading models. The optimal usage of loading models is still to be defined in all possible applications.
The goal of this working group is to study the optimal usage of load models for TRF utilization.
Objectives
The principal objectives of the scientific work are to investigate optimal methods for applying load corrections for TRF development and usage, and to assemble specific recommendations for users.
Specific program activities
- Compare and assess differences between existing load models for a given effect
- develop forward model of ice loading at high latitudes
- monitor geocenter motion variations to identify possible accelerations
- Maintain a bibliography on the available models and their evaluation.
- Assessment of the propagation of loading model errors into the site coordinates and the ITRF.
- Define whether models should be applied at the observation level or in the post-processing. In this case, define the best method (if any) to handle loading effects at the observation level (filtering?, interpolation etc…).
- Tie results/findings to IERS conventions.
- Collect user opinions about what signals they need in station position time series (loading corrected or not).
Members
- Tonie van Dam (Luxembourg), Chair
- Anthony Mémin (France), Vice-chair
- Zuheir Altamimi (France)
- Johannes Böhm (Austria)
- Jean-Paul Boy (France)
- Xavier Collilieux (France)
- Robert Dill (Germany)
- Pascal Gegout (France)
- Matt King (Australia)
- Anthony Mémin (France)
- Laurent Métivier (France)
- Gerard Petit (France)
- Jim Ray (USA)
- Leonid Vitushkin (Russia)
- Xiaoping Wu (China)
Working title: Troposphere Ties
Joint with IAG SC 4.3
Chair: Robert Heinkelmann (Germany)
Vice-Chair: Jan Douša, (Czech Republic)
Terms of Reference
Since many years, tropospheric parameters have been determined by space geodetic techniques, by other measurement techniques, such as water vapor radiometers, and, more recently, from model data, e.g. from numerical weather models. As tropospheric parameters we designate the hydrostatic and wet or total zenith delays and the horizontal gradients. Many comparative studies have revealed that besides statistical deviations the tropospheric parameters partly exhibit systematic differences. Such systematic differences might be caused by
- General differences, e.g. the different locations of the sensors, the different epochs of the observations and other e.g. meteorological ambient conditions;
- Effects due to hardware and hardware changes, e.g. change of the type of the GNSS antenna or effect of a radome at a station;
- The inter-technique systematics, for example due to different correlations among groups of parameters and / or due to the different sampling and geometry of observations;
- The application of different analysis models, such as the mapping functions, the different parameterizations used to represent the troposphere and the application of constraints during the adjustment, and, in addition;
- The post-processing methods of data handling for the comparison, e.g. the application of synchronization methods, such as interpolation, filtering, smoothing.
The terrestrial reference frame (TRF) is commonly realized by a combination of space geodetic techniques. For the combination of the techniques ‘global ties’, i.e. common global parameters, like the Earth Orientation Parameters (EOP), can be directly used, while ‘local ties’, i.e. common coordinates at co-location sites, have to consider the distances between the reference points of the various devices. The distances between the reference points are usually surveyed at site, but can also be indirectly assessed through the comparison of the positions determined by the various space geodetic techniques. The ground-based space geodetic techniques all observe targets in or above the atmosphere and consequently common atmospheric parameters might be used to link the techniques as well. The systematics between tropospheric parameters obtained by different sensors have to be considered to reasonably perform this combination approach. With ‘tropospheric ties’ we designate the systematics that enable a combination of tropospheric parameters if they are appropriately considered.
Objectives
The main objective of the working group is (i) to assess the systematics between tropospheric parameters obtained at different locations, times, and by different measurement techniques: tropospheric ties. The other focus is (ii) to test the application of tropospheric ties for the combination of the space geodetic techniques. Accordingly, the group will work on
- Extensive comparisons of tropospheric parameters;
- Theoretical modeling based on hydrostatic equilibrium and comparable assumptions;
- Numerical modelling involving numerical weather models; and
- Testing the combination with the application of the tropospheric ties.
Members
- Robert Heinkelmann (Germany), Chair
- Jan Douša (Czech Republic), Vice-chair
- Kyriakos Balidakis (Germany)
- Elmar Brockmann (Switzerland)
- Sebastian Halsig (Germany)
- Gregor Möller (Austria)
- Angelyn W. Moore (USA)
- Tobias Nilsson (Germany)
- Rosa Pacione (Italy)
- Tzvetan Simeonov (Bulgaria)
- Krzysztof Sosnica (Poland)
- Peter Steigenberger (Germany)
- Kamil Teke (Turkey)
- Daniela Thaller (Germany)
- Xiaoya Wang (China)
- Pascal Willis (France)
- Florian Zus (Germany)
Definition of Next Generation Terrestrial Reference Frames
Joint with ICCT and GGOS
Chair: C. Kotsakis (Greece)
Link to the WG website at ICCT
Strategy for the Realization of the International Height Reference System (IHRS)
Joint with GGOS Focus Area 1, Commission 2, ICCT and IGFS
Chair: L. Sanchez (Germany)
Relativistic Geodesy: First Steps Towards a New Geodetic Technique
Joint with Commission 2 and ICCT
Chair: Jakob Flury (Germany)