The Global Geodetic Observing System (GGOS) provides measurements of the time varying gravity, rotation, and shape of the Earth using geodetic and gravimetric instruments located on the ground and in space. These measurements need to be accurate to better than a part per billion in order to advance our understanding of the underlying processes that are causing the Earth's rotation, gravity, and shape to change. Mass transport in the global water cycle, sea level and climate change, and crustal deformation associated with geohazards are examples of particularly demanding applications of geodetic and gravimetric measurements. All these measurements require a common reference with the same precision, like the Terrestrial Reference Frame and the Unified Height System. GGOS is designed to unite the individual observations and model into one consistent frame with the highest precision available. This session should be a platform for discussing improvements to global geodetic observing systems including multidisciplinary approaches as well as for single contributions with high precision in a global network.

The Terrestrial Reference Frame is fundamental for monitoring Earth rotation in space and for all geoscience applications that require absolute positioning and precise orbit determination of artificial satellites. The goal of this session is to provide a forum to discuss reference systems theory, realization and applications in geosciences and society, with a special emphasis on the scientific applications of the International Terrestrial Reference Frame (ITRF), and namely the ITRF2014. Participants can discuss concerns not only related to the contributing technique services, but also all ITRF uses, ranging from local, regional to global applications. Contributions are sought from the individual technique services and various ITRF users, covering the complete range of topics, such as data analysis, parameter estimation and correction models. Of special interest is the assessment of the impact of non-linear station motions, e.g. periodic signals and post-seismic deformations. Contributions by the technique services related to the preparation of ITRF2020 focusing especially on identifying and mitigating technique systematic errors are highly appreciated. Contributions on local tie survey methodology are also welcome.

Precise orbit determination is of central importance for many applications of geodesy and earth science. The challenge is to determine satellite orbits in an absolute sense at the centimeter or even sub-centimeter level, and at the millimeter or even sub-millimeter level in a relative sense. New constellations of GNSS satellites are currently being completed and numerous position-critical missions (e.g. altimetry, gravity, SAR and SLR missions) are currently in orbit. All together outstanding data are available offering new opportunities to push orbit determination to the limit and to explore new applications.

This session aims to make accessible the technical challenges of orbit determination and modelling to the wider community and to quantify the nature of the impact of dynamics errors on the various applications. Contributions are solicited but not limited to the following areas: (1) precise orbit determination and validation; (2) satellite surface force modelling; (3) advances in modelling atmospheric density and in atmospheric gravity; (4) advances in modelling earth radiation fluxes and their interaction with space vehicles; (5) analysis of changes in geodetic parameters/earth models resulting from improved force modelling/orbit determination methods; (6) improvements in observable modelling for all tracking systems, e.g. SLR, DORIS, GNSS and their impact on orbit determination; (7) advances in combining the different tracking systems for orbit determination; (8) the impact of improved clock modelling methods/space clocks on precise orbit determination; (9) advances in modelling satellite attitude.

The geodetic products that describe the system Earth are of high quality, although the Global Geodetic Observing System (GGOS) goals of 1 mm accuracy and 0.1 mm/yr stability for the terrestrial reference frame, the Earth Orientation Parameters (EOPs) and the static and time-variable gravity field of the Earth are not yet fully reached. There are limiting factors that need to be detected, analyzed, and quantified. In this context, the usage of a sub-set of available observations only, degrading station equipment quality, limitations in the observing concepts and analysis and combination methods evoke the question whether and how the derived Earth system products can be improved.
In principle, there are two ways to investigate the best methods for improving geodetic products. (A) New strategies of handling, analyzing and combining the already existing space-geodetic observations need to be developed. (B) The existing observing infrastructure should be extended by new stations, new satellite missions, and new types of observations or new observing concepts. In the latter case, simulation studies are indispensable.
This session provides a platform for presentations of new strategies, new analysis methods and simulation studies seeking to improve the determination of Earth system parameters and geodetic products such as the Terrestrial and Celestial Reference Frame (TRF, CRF), EOPs, Earth’s gravity field, satellite orbits, as well as atmospheric key parameters. Presentations investigating approaches for reaching a better consistency between the individual parameters are highly welcomed, e.g., studies towards consistent estimation of the TRF, CRF and EOPs. Concerning consistency, novel approaches to achieve a consistent estimation of the three pillars of geodesy, i.e., geometry, orientation and gravity, are also welcomed. In addition we are seeking contributions focusing on alternative analysis concepts such as employing co-locations in space, clock ties, or atmospheric ties. Simulation studies investigating dedicated co-location satellites or novel observation methods (e.g. inter-satellite links or VLBI tracking of GNSS satellites) and their potential for improving the geodetic parameters are also invited. Many of the aspects mentioned above are brought together within the GGOS Standing Committee PLATO (Performance Simulations and Architectural Trade-Offs). Therefore, contributions related to the activities carried out within this group are also appreciated.