Remarkable advances over recent years give an evidence that geodesy today develops under a broad spectrum of interactions, including theory, science, engineering, technology, observation, and practice-oriented services. Geodetic science accumulates significant results in studies towards classical geodetic problems and also problems that only emerged or gained new interest, in many cases as a consequence of synergistic activities in geodesy and tremendous advances in the instrumentations and computational facilities. In-depth studies progressed in parallel with investigations that mean a broadening of the traditional core of geodesy. The scope of the session is conceived with a certain degree of freedom, though the session is primarily intended to provide a forum for all investigations and results of theoretical and methodological nature.

Within this concept we seek contributions concerning problems of reference frames, gravity field studies, dynamics and rotation of the Earth, positioning, but also presentations, which surpass frontiers of these topics. We invite presentations illustrating the use of mathematical and numerical methods in solving geodetic problems, showing advances in mathematical modeling, estimating parameters, simulating relations and systems, using high-performance computations, and discussing also methods that enable to exploit data essentially associated with new and existing satellite missions. Presentations showing mathematical and physical research directly motivated by geodetic need, practice and ties to other disciplines are welcome. In parallel to theory oriented results also examples illustrating the use of new methods on real data in various branches of geodetic science and practice are very much solicited in this session.

The analysis of potential fields, especially of the Earth's gravity and magnetic fields, is becoming increasingly important for the geosciences community. The modern satellite missions are continuing to provide data with ever improving accuracy and nearly global, time-dependent coverage. The gravitational field, respectively the geoid, plays an important role in climate research, as a record of and reference for the observation of mass transport. The study of the Earth's magnetic field and its temporal variations is yielding new insights into the behavior of its internal and external sources. Both gravity and magnetic data furthermore constitute primary sources of information also for the global characterization of other planets. With this vast quantity of data and the richness of research topics that can be addressed with it, there continues to be a need to develop new methods of analysis, at the global and local scales, and especially on their interface, where high- and low resolution data are to be jointly represented and interpreted, and where global/local contributions to noise/signal need to be differentiated. Global fields have traditionally been modeled in the spherical harmonics basis; local observations typically in a Cartesian space-based or Fourier framework. For over two decades now, methods that combine global with local sensitivity, often in a multiresolution setting, have been developed as alternatives: these include wavelets, radial basis functions, Slepian functions, splines, spherical cap harmonics, etc. With these, a growing range of problems can be addressed, but many further developments, including particular aspects of their algorithmic implementation, or the explicit search for sparsity in the modeling domain are awaiting further study. On the one hand side the purpose of this session is to provide a forum for exchange on the current state-of-the-art on these research topics, whether related to forward or inverse modeling, theoretical, computational, or observational studies. Especially studies on regional gravity field modeling from the combination of different input data sets as well as comparisons between different solutions are welcome.

On the other hand, besides monitoring the variations of the Earth's gravity and magnetic fields, space geodetic techniques deliver time series describing changes of the surface geometry, sea level change variations or fluctuations in the Earth's orientation. However, geodetic observation systems usually measure the integral effect of all effects. Thus, analysis methods have to be applied to the geodetic time series for a better understanding of the relations between and within the components of the system Earth. The combination of data from various space geodetic and remote sensing techniques may allow for separating the integral measurements into individual contributions of the Earth system components. Presentations to time frequency analysis, to the detection of features of the temporal or spatial variability of signals existing in geodetic data and in geophysical models, as well as to the investigations on signal separation techniques, e.g. EOF, are highly appreciated. We further solicit papers on different prediction techniques e.g. least-squares, neural networks, Kalman filter or uni- or multivariate autoregressive methods to forecast Earth Orientation Parameters, which are needed for real-time transformation between celestial and terrestrial reference frames.

In the past two decades high-precision GPS has been applied to support numerous applications in Geosciences. Currently, there are two fully operational Global Navigation Satellite Systems (GNSS), and two more are in the implementation stage. The new Galileo and BDS systems already provide usable signals, and both, GPS and GLONASS, are currently undergoing a significant modernization, which adds more capacity, more signals, better accuracy and interoperability, etc. Meanwhile, the huge technology development provided GNSS equipment (in some cases even at low-cost) able to collect measurements at much higher rates, up to 100 Hz, hence opening new possibilities. Therefore, on one side, the new developments in GNSS stimulate a broad range of new applications for solid and fluid Earth investigations, both in post-processing and in real-time; on the other side, this, results in new problems and challenges in data processing which boost GNSS research. Algorithmic advancements are needed to address the opportunities and challenges in enhancing the accuracy, availability, interoperability and integrity of high-precision GNSS applications.

This session is related to activities of IAG SC4.4 'Multi-constellation GNSS' and IAG-ICCT JSG 0.10 'High-rate GNSS'. It is a forum to discuss new developments in high-precision GNSS algorithms and applications in Geosciences; in this respect, contributions from other branches in Geosciences (geodynamics, seismology, tsunamis, ionosphere, troposphere, etc.) are very welcome.

We encourage, but not limit, submissions related to:
- Modeling and strategies in high-precision GNSS,
- Multi-GNSS benefit for Geosciences,
- Multi-GNSS processing and product standards,
- Inter-system and inter-frequency biases and calibrations,
- New or improved GNSS products for high-precision applications (orbits, clocks, UPDs, etc.),
- Precise Point Positioning (PPP, PPP-RTK),
- High-rate GNSS,
- GNSS and other sensors (accelerometers, INS, ecc.) integration for high-rate applications,
- Ambiguity resolution and validation,
- CORS services for Geosciences (GBAS, Network-RTK, etc.),
- Precise Positioning of EOS platforms,
- Precise Positioning for natural hazards prevention,
- Monitoring crustal deformation and the seismic cycle of active faults,
- GNSS and early-warning systems,
- GNSS reflectometry,
- High-precision applications for Geosciences,
- and more.