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 modelling, 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 the Earth's gravity and magnetic fields is becoming increasingly important in geosciences. Modern satellite missions are continuing to provide data with ever improving accuracy and nearly global, time-dependent coverage. The gravitational field 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. Hence, there continues to be a need to develop new methods of analysis, at the global and local scales, and especially on their interface. For over two decades now, methods that combine global with local sensitivity, often in a multiresolution setting, have been developed: these include wavelets, radial basis functions, Slepian functions, splines, spherical cap harmonics, etc. One purpose of this session is to provide a forum for exchange of research projects, whether related to forward or inverse modeling, theoretical, computational, or observational studies.
Besides monitoring the variations of the 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. 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 recent years we have witnessed a remarkable progress in terms of signals, services and satellite deployment of Global Navigation Satellite Systems (GNSS). The modernization of fully operational GNSS systems and the development of new constellations, have seen us move towards a new stage of multi-constellation and multi-frequency observations. 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 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:
- Modelling and processing strategies in high-precision GNSS,
- Multi-GNSS benefit for Geosciences,
- Multi-GNSS processing and product standards,
- Inter-system and inter-frequency biases,
- New or improved GNSS products for high-precision applications (orbits, clocks, UPDs, etc.),
- Precise Point Positioning (PPP, PPP-RTK) and Real Time Kinematic (RTK),
- High-rate GNSS,
- GNSS and other sensors (accelerometers, INS, etc.) 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,
- Low-cost receivers and smartphone GNSS observations for precise positioning, navigation and geoscience applications.

This session aims to showcase novel applications of data science and machine learning methods in geodesy.

In recent years, the amount of data from geodetic observation techniques has increased dramatically. Innovative approaches are required to efficiently handle and harness the vast amount of geodetic data available nowadays for scientific purposes. In particular, Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) are facing challenges, but also opportunities, related to the expansive data collection (“big data”). Similarly, numerical weather models and other geophysical models important for geodesy come with ever growing resolutions and dimensions. Strategies and methodologies from the fields of data science and machine learning have shown great potential not only in this context, but also when applied to more limited data sets to solve complex non-linear problems in geodesy.

We invite contributions related to various aspects of applying methods from data science and machine learning (including both shallow and deep learning techniques) to geodetic problems and data sets. We welcome investigations related to (but not limited to): more efficient and automated processing of geodetic data, pattern and anomaly detection in geodetic time series, images or higher-dimensional data sets, improved predictions of geodetic parameters into the future, combination and extraction of information from multiple inhomogeneous data sets (multi-temporal, multi-sensor, multi-modal fusion), feature selection, super-sampling of geodetic data, and improvements of large-scale simulations. Especially encouraged are contributions that discuss the uncertainty quantification, interpretability and explainability of results from machine learning algorithms, as well as the integration of physical modeling into data-driven frameworks.

This session will focus on the practical solution of various formulations of geodetic boundary-value problems to yield precise local and regional high-resolution (quasi)geoid models. Contributions describing recent developments in theory, processing methods, downward continuation of satellite and airborne data, treatment of altimetry and shipborne data, terrain modeling, software development and the combination of gravity data with other signals of the gravity field for a precise local and regional gravity field determination are welcome. Topics such as the comparison of methods and results, the interpretation of residuals as well as geoid applications to satellite altimetry, oceanography, vertical datums and local and regional geospatial height registration are of a special interest.

The Global Geodetic Observing System (GGOS) provides measurements of the time varying gravity, rotation, and shape of the Earth using space and terrestrial geodetic techniques. These measurements need to be accurate to better than a part per billion in order to advance our understanding of the underlying processes responsible for temporal changes in the Earth's rotation, gravity, and shape. Demanding applications of geodetic measurements include mass transport in the global water cycle, sea level and climate change, and crustal deformation associated with geohazards. 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 welcomes contributions on general GGOS topics, particularly those related to scientific aspects of GGOS applications, e.g. improvement of infrastructure, development of new sensors, and proposals of multidisciplinary approaches to achieve specific goals in earth science.

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, data analysis improvement, realization and applications in geosciences and society, with a special emphasis on the scientific applications of the International Terrestrial Reference Frame (ITRF), and namely its next release, the ITRF2020. 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 for ITRF2020 focusing especially on identifying and mitigating technique systematic errors are highly appreciated. Contributions on local tie survey methodology are also welcome.

The geodetic products that describe the Earth system 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 (TRF), 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 as well as deficiencies in the 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 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. To realize new observing concepts, 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. Novel approaches to achieve a consistent estimation of the three pillars of geodesy, i.e., geometry, orientation and gravity, are highly welcomed. Investigations reaching for a better consistency between the individual parameters and between the products (TRF, CRF, EOP, gravity field) are also welcomed. In addition, we are seeking contributions focusing on new combination approaches and 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 highly encouraged.

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.

This session intends to showcase climate related studies which have made use of geodetic observations and or techniques.
Modern geodetic observing systems are sensitive to a wide range of changes in the Earth’s solid and fluid layers at very diverging spatial and temporal scales related to processes as, e.g., glacial isostatic adjustment, the terrestrial water cycle, ocean dynamics, sea-level and ice-mass balance. Geodetic observables are often compared with geophysical models, which helps to explain observations, evaluate simulations, and may potentially be used to improve simulations through techniques such as data assimilation.

We invite contributions utilizing geodetic data from e.g. altimetry, gravimetry (CHAMP, GRACE, GOCE and GRACE-FO), navigation satellite systems (GNSS and DORIS) or remote sensing techniques that are based on both passive (e.g. optical and multi/hyperspectral) and active (i.e., SAR) instruments. New approaches helping to separate and interpret the variety of geophysical signals present in observations are equally appreciated.

The session closely adheres to the ideas of the recently established Inter-Commission Committee on "Geodesy for Climate Research" (ICCC) of the International Association of Geodesy (IAG), which aims to encourage collaborations between the climate and geodetic community and promote the use of geodetic observations and principles while at the same time benefiting from climate expertise in the interpretation and correction of geodetic observations. We encourage authors to tailor their presentations to include non-geodetic scientists as their audience, and, with the author’s consent, highlights from this session will be tweeted in order to increase visibility.

Accurate modeling and prediction of Earth rotation is of paramount importance in many disciplines, e.g., geodesy, astronomy and navigation. Over the past years geodetic observation systems have made significant advances in monitoring Earth rotational motion and its variability. That progress must be accompanied by an enhancement of the theories, conventional models, etc., as was recently recognized in Resolution 5 adopted at last IAG GA (Montreal, 2019).
In this session, we are interested in the progress in the theory of Earth rotation. We seek contributions that are consistent internally with the accurate observations at the mm-level, to meet the requirements of Global Geodetic Observing System (GGOS) and respond to IAG Res. 5. We invite presentations within the scope of the IAU/IAG JWG Improving Theories and Models of the Earth’s Rotation.
We welcome contributions that highlight new determinations and analyses of Earth Orientation Parameters (EOP) series, including combinations of different geodetic and astrometric observational techniques. We welcome discussions of EOP solutions in conjunction with a consistent determination of terrestrial and celestial frames, as tackled in the IAG/IAU/IERS JWG Consistent Realization of TRF, CRF and EOP.
We invite contributions of both the dynamical basis for links between Earth rotation, geophysical fluids, and other geodetic quantities, such as the Earth gravity field or surface deformation, and of investigations leading to detailed explanations for the physical excitations of Earth rotation. Besides tidal influences from outside the Earth, the principal causes for variable EOP appear to be related to angular momentum exchange from variable motions and mass redistribution of the fluid portions of the planet. Observations of the geophysical fluids (e.g., atmosphere and oceans) have achieved a new maturity in recent years. Independent observations include the results of recent gravity missions like GRACE.
We welcome contributions about the relationship between EOP variability and current or potential variability in fluids due to climate variation or global change signals. Forecasts of these quantities are important especially for the operational determination of Earth orientation and its application, e.g., spacecraft navigation; the effort to improve predictions currently is a topic of strong interest. We welcome input on the modeling, variability, and excitations of the rotation of other celestial bodies.

Satellite altimetry provides the possibility to observe key parts of the hydrosphere, namely the ocean, ice, and continental surface water from space. Since the launch of Topex/Poseidon in 1992 the applications of altimetry have expanded from the open oceans to coastal zones, inland water, land and sea ice. Today, seven missions are in orbit, providing dense and near-global observations of surface elevation and several other parameters. Satellite altimetry has become an integral part of the global observation of the Earth‘s system and changes therein.

In recent years, new satellite altimetry missions have been launched carrying new instruments; the CryoSat-2/Sentinel-3 missions equipped with a Delay/Doppler altimeter, the Saral AltiKa mission carrying the first Ka band altimeter, and the 2018 launched six beam photon counting laser altimeter on-board NASAs ICESat-2. Further, new orbits with high inclination and long-repeat time are used for CryoSat-2 and ICESat-2.


Fully exploiting this unprecedented availability of observables will enable new applications and results but also require novel and adapted methods of data analysis.
Across the different applications for satellite altimetry, the data analysis and underlying methods are similar and a knowledge exchange between the disciplines has been proofed to be fruitful.
In this multidisciplinary altimetry session, we therefore invite contributions which discuss new methodology and applications for satellite altimetry in the fields of geodesy, hydrology, cryosphere, oceanography, and climatology.
Topics of such studies could for example be (but not limited to); creation of robust and consistent time series across sensors, validation experiments, combination of radar and laser altimetry for e.g. remote sensing of snow, classification of waveforms, application of data in a geodetic orbit, retracking, or combination with other remote sensing data sets.

Growth and decay of ice sheets and glaciers reshape the solid Earth via isostasy and erosion. In turn, the shape of the bed exerts a fundamental control on ice dynamics as well as the position of the grounding line—the location where ice starts to float. Additionally, this behaviour is affected by large spatial variations in rheological properties of the Earth's subsurface. These properties govern the timescale and strength of feedbacks between ice-sheet change and solid Earth deformation, and hence must be accounted for, e.g., when considering the future evolution of the Polar Ice Sheets. This session invites contributions discussing geodetic, geological and geophysical observations (such as deformation fields and past sea-level indicators), analyses, and modelling of the coupling of the Solid Earth and glacial isostatic adjustment (GIA) and/or addressing the Earth properties from seismological, gravity, magnetic and heat-flow studies. We welcome contributions related to both polar regions and previously glaciated areas. We also welcome contributions highlighting the effect of GIA on tectonical processes and petroleum reservoirs, and the GIA contribution in natural hazard assessments.

Invited Speaker: Harriet Lau, University of California, Berkeley, USA

Slip at faults generate ground motion over a wide range of time-scales, from milliseconds to decades and centuries. While geodesy and seismology have been used independently in the past to study the fault behavior, new capabilities in space geodesy as well as seismology analysis argue for a further integration of both disciplines. A non-limitative list of progresses include the development of continuous GNSS networks allowing to monitor motion over a frequency bandwidth overlapping with seismology, new radar satellite missions, optic imaging capabilities allowing to capture new signals, before, during and after earthquakes, new detection techniques of seismic signal and the ability to build high quality earthquakes, tremors and low-frequency earthquakes catalogues, opening new prospects for the study of the Earth’deformation and earthquakes.

This session will gather colleagues interested in integrating seismological and geodetic observations, data, and analysis to better understand the Earth’s deformation and earthquakes. Welcome are contributions about new technologies aiming at improving our ability to monitor ground motion at various time-scales inland and offshore at the sea-floor.
Comparison, validation and dissemination of high-quality accessible data and software are also encouraged. Finally, we encourage submission of joint analysis integrating seismology and geodesy to better understand earthquakes from regional to local approaches. Detection and characterization of transient slip through their joint geodetic and seismic signatures are most welcome.

This session is proposed by the joint IAG-IASPEI Seismo-geodesy sub-commission.

The evolution of the large ice sheets and the Earth’s rheology control the process of glacial isostatic adjustment, while bedrock topography and geothermal heat flux have strong feedbacks on ice sheet dynamics. For changing climates, this interplay exerts a fundamental control on the global and regional sea level and, in turn, influences ice sheet stability.

In this session, we focus on feedback mechanisms between climate relevant components, such as ice sheets, ice shelves, solid Earth, oceans and atmosphere (e.g., as in the German Climate modelling initiative PalMod). We invite global, regional and conceptual studies that consider reconstructions of the past and/or estimates of future ice sheet evolution in fields related to the climate system dynamics of glacial processes (the cryosphere, geosphere, oceanography, climatology, geodesy and geomorphology). In particular, we welcome studies of recent and paleo observations (geodetic, geological, geophysical), coupled numerical modelling and strategies, data-constrained model calibration and data assimilation.

We welcome submissions on all aspects of tides in the ocean, atmosphere and solid Earth, from regional to global scales and covering all time scales on Earth and other planets. Tides impact many Earth system processes such as ocean mixing, global ocean circulation, ice sheet dynamics and biogeochemical processes. Tides interacting with storm surges and sea level rise can cause coastal flooding, and harnessing of tidal energy can provide a source of renewable energy. Accurate tide models are necessary for the analysis of satellite gravimetry and altimetry data, especially in light of the upcoming Surface Water Ocean Topography (SWOT) mission.
We encourage contributions on progress in numerical modelling of both surface and internal tides and assessments of their accuracy, observations of long-term changes in tides and tidal processes on global to regional scales, insights on tidal variability from global geodetic observing techniques, and research into the role of tides in shaping Earth’s evolutionary processes. We also invite submissions on tidal dynamics in estuaries, rivers and lakes.

Low-lying coastal areas can be an early casualty to the acceleration of sea-level rise, especially where enhanced by land subsidence. An ever increasing number of studies indicates that land subsidence due to natural and anthropogenic causes has induced damage to wetland ecosystems in many countries worldwide, and increased flooding hazard and risk. Coastal subsidence causes include excessive groundwater extraction from aquifers, peat oxidation due to surface water drainage through land reclamation, urbanization and agricultural use, as well as sediment starvation due to construction of dams and artificial levees. Contrary to the global processes behind sea-level rise, natural and anthropogenic coastal subsidence is primarily a local phenomenon, and causes and severity may vary substantially from place to place.

The combination of geological and historical measurements with remote sensing data is required to understand all drivers of coastal vertical land motion and the contributions to past, present, and future subsidence. Understanding coastal subsidence requires multidisciplinary expertise, including measuring and modeling techniques from geology, geodesy, natural hazards, oceanography, hydrogeology, and geomechanics. In this session, we aim to bring together all the involved disciplines. We invite contributions on all aspects of coastal subsidence research and applications, including recent advances on: i) measurement through ground-based, aerial and satellite remote sensing techniques, ii) numerical models and future projections, iii) their applicability to distinguish between the different drivers contributing to land subsidence, and iv) quantification of coastal hazards associated with relative sea-level rise. In particular, efforts towards characterizing human intervention on coastal vertical land motion are welcomed.

The session deals with the documentation and modelling of the tectonic, deformation and geodetic features of any type of volcanic area, on Earth and in the Solar System. The focus is on advancing our understanding on any type of deformation of active and non-active volcanoes, on the associated behaviours, and the implications for hazards. We welcome contributions based on results from fieldwork, remote-sensing studies, geodetic and geophysical measurements, analytical, analogue and numerical simulations, and laboratory studies of volcanic rocks.
Studies may be focused at the regional scale, investigating the tectonic setting responsible for and controlling volcanic activity, both along divergent and convergent plate boundaries, as well in intraplate settings. At a more local scale, all types of surface deformation in volcanic areas are of interest, such as elastic inflation and deflation, or anelastic processes, including caldera and flank collapses. Deeper, sub-volcanic deformation studies, concerning the emplacement of intrusions, as sills, dikes and laccoliths, are most welcome.
We also particularly welcome geophysical data aimed at understanding magmatic processes during volcano unrest. These include geodetic studies obtained mainly through GPS and InSAR, as well as at their modelling to imagine sources.


The session includes, but is not restricted to, the following topics:
• volcanism and regional tectonics;
• formation of magma chambers, laccoliths, and other intrusions;
• dyke and sill propagation, emplacement, and arrest;
• earthquakes and eruptions;
• caldera collapse, resurgence, and unrest;
• flank collapse;
• volcano deformation monitoring;
• volcano deformation and hazard mitigation;
• volcano unrest;
• mechanical properties of rocks in volcanic areas.

On 29 December 2020, a major earthquake (Mw 6.4) occurred in Croatia close to Petrinja, only nine months after another Mw 5.5 damaging earthquake in Zagreb, the capital city located 45 km north of Petrinja. The December shock is the strongest event in continental Europe since the Norcia sequence (Italy) in 2016 and was caused by the rupture of a NW-SE dextral strike-slip fault at the boundary between the Dinarides and the Pannonian basin ; it was preceded by two strong foreshocks (M~5) the day before. Seismic shaking was widely felt across Europe, and caused extensive damage to buildings and infrastructures in the epicentral region. The earthquake resulted in liquefaction over large areas, and many cracks and a surface rupture have been observed in the field.
This late-breaking session aims at gathering contributions to discuss the 2020 Petrinja earthquake sequence, its surface effects on human and natural environment in terms of shaking and faulting. We encourage presentations dealing with the seismological, geodetical or geological observations related to this earthquake and the ongoing seismic sequence, as well as insights on the regional faults, their historical seismicity or recent geological activity. All this together can help in understanding the geodynamics of this seismically active but poorly characterized region.

Current developments in quantum physics enable novel applications and measurement concepts in geodesy and Earth observation. In this Session, we will discuss new sensors and mission concepts that apply advanced techniques for the study of the gravitational field of the Earth on ground and in space. Terrestrial gravity anomalies will be determined by observing free-falling atoms (quantum gravimetry) gradually replacing the falling corner cubes. This technique can also be applied for future gradiometric measurements in space.
According to Einstein’s theory of general relativity, frequency comparisons of highly precise optical clocks connected by optical links give access to differences of the gravity potential (relativistic geodesy) for gravity field recovery and height determination. In future, precise optical clocks can be applied for defining and realizing height systems in a new way, and moreover, help to improve the accuracy of the International Atomic Time scale TAI. They are important for all space geodetic techniques as well as for the realization of reference systems and their connections.
Additionally, laser interferometry between test masses in space with nanometer accuracy – which has been realized as a demonstrator in the GRACE-FO mission – belongs to these novel concepts, and in the future even more refined concepts (tracking swarms of satellites, space gradiometry) will be realized.
Finally, changes in the gravity field can be derived from GNSS displacements which play an increasingly important role due to the relatively cheap and easy deployment of new GNSS receivers and the large number of available stations.
These techniques will open the door for a vast bundle of applications such as fast local gravimetric surveys and exploration, and the gravimetric observation of the Earth system from space with high spatial and temporal resolution. So, mass variations can be monitored at various scales providing unique information on climate change processes.
We invite presentations to illustrate the principles and state of the art of those novel techniques and the application of the new methods for terrestrial and satellite geodesy, navigation and fundamental physics. We also welcome papers for further applications and invite contributions covering the theoretical description of the new methods, introducing novel theoretical concepts as well as new modelling schemes.

For about two decades now, satellite missions dedicated to the determination of the Earth's gravity field have enabled a wide variety of studies related to climate research as well as other geophysical or geodetic applications. Continuing the successful, more than 15 years long data record of the Gravity Recovery and Climate Experiment (GRACE, 2002-2017) mission, its Follow-on mission GRACE-FO, launched in May 2018, is currently in orbit providing fundamental observations to monitor global gravity variations from space. Regarding the computation of high-resolution static gravity field models of the Earth and oceanic applications, the Gravity field and steady-state Ocean Circulation Explorer (GOCE, 2009-2013) mission plays an indispensable role. Complementary to these dedicated missions, observations from other non-dedicated missions such as Swarm as well as satellite laser ranging (SLR) have shown to be of significant importance, either to bridge gaps in the GRACE/GRACE-FO time series or to improve gravity field models and scientific results derived thereof. The important role of satellite gravimetry in monitoring the Earth from space has led to various ongoing initiatives preparing for future gravity missions, including simulation studies, the definition of user and mission requirements and the investigation of potential measurement equipment and orbit scenarios.

This session solicits contributions about:
(1) Results from satellite gravimetry missions as well as from non-dedicated satellite missions in terms of
- data analyses to retrieve time-variable and static global gravity field models,
- combination synergies, and
- Earth science applications.
(2) The status and study results for future gravity field missions.

Gravity and magnetic field data contribute to a wide range of geo-scientific research, from imaging the structure of the earth and geodynamic processes (e.g. mass transport phenomena or deformation processes) to near surface investigations. The session is dedicated to contributions related to spatial and temporal variations of the Earth gravity and magnetic field at all scales. Contributions to modern potential field research are welcome, including instrumental issues, data processing techniques, interpretation methods, innovative applications of the results and data collected by modern satellite missions (e.g. GOCE, GRACE, Swarm), potential theory, as well as case histories.

Terrain gravimetry is a powerful geophysical tool that, through sensing changes in subsurface mass, can supply unique information on the dynamics of underground fluids, like water, magma, hydrocarbons, etc. This is critically important for energy industry (not just petroleum and natural gas, but also geothermal), resource management (particularly, with regard to water), and natural hazards (especially volcanoes).
Despite its potential, terrain gravimetry is currently underexploited, owing to the high cost of available instrumentation and the difficulty in using it under harsh environmental conditions and to the major challenge posed by retrieving useful information from gravity changes in noisy environments.
Major technology developments have recently occurred in instrumentation and methodology and are being demonstrated, opening up new perspectives to increase the capability of terrain gravimetry. On one hand, new types of sensors are being developed and ruggedized, expanding the measurement capabilities. On the other hand, methodologies and workflows are developed to exploit more efficiently hybrid networks of sensors. As an example, a recently funded H2020 project, called NEWTON-g, targets the development and field application of a “gravity imager” exploiting MEMS (relative) and quantum (absolute) gravimeters. These advancements will give new impulse to terrain gravimetry, thus helping its transition from a niche field into a cornerstone resource for geophysical monitoring and research. However, for this transition to succeed, technology developments must be complemented by constructive feedback from the gravimetry community
This session aims at bringing together instrument and tool developers and end-users of terrain gravimetry in a variety of fields, including, but not limited to, hydrology, volcanology and petroleum geology. We aim at discussing the state of the art of terrain gravimetry and the added value it provides with respect to other geophysical techniques, as well as the exciting opportunities offered by the new technologies under development.

The term space weather indicates physical processes and phenomena in space caused by the radiation of energy mainly from the Sun. Solar and geomagnetic storms can cause disturbances in positioning, navigation and communication; coronal mass ejections (CME) can affect serious disturbances and in extreme cases damages or even destruction of modern infrastructure. The ionosphere and the thermosphere are parts of a physically coupled systems ranging from the Earth surface to the Sun including the magnetosphere and the lower atmosphere. Therefore, conducting detailed investigations on governing processes in the solar-terrestrial environment have key importance to understand the spatial and temporal variations of ionospheric and thermospheric key parameters such as the total electron content (TEC) and the plasma density of the ionosphere, as well as the thermospheric neutral density, which are influencing the orbits of Low-Earth orbiting (LEO) satellites. To address all these interrelations and impacts, the Global Geodetic Observing System (GGOS) Focus Area on Geodetic Space Weather Research was implemented into the structure of the International Association of Geodesy (IAG).

This session will address recent progress, current understanding, and future challenges of thermospheric and ionospheric research including the coupling processes. Special emphasise is laid on the modelling and forecasting of space weather time series, e.g. EUV-, X-ray radiation and CMEs, and their impact on VTEC and electron density. We encourage further contributions to the dynamo electric field, the variations of neutral and ion compositions on the bottom and top side of the ionosphere, atmospheric gravity waves and TIDs. Furthermore, we appreciate contributions on the wind dynamo, electrodynamics and disturbances, including plasma drift, equatorial spread F, plasma bubbles, and resultant scintillation.

Another main topic is global and regional high-resolution and high-precision modelling of VTEC and the electron density based on empirical, analytical or physical data assimilation approaches, which are designed for post-processing or (near) real-time purposes.

Geodesy contributes to Atmospheric Science by providing some of the ECVs of the GCOS. Water Vapor is under-sampled in the current meteorological and climate observing systems. Obtaining more high-quality humidity observations is essential to weather forecasting and climate monitoring. The production, exploitation and evaluation of operational GNSS-Met for weather forecasting is well established in Europe due to 20+ years of cooperation between the geodetic community and the national met services. Advancements in NWP models to improve forecasting of extreme precipitation require GNSS troposphere products with a higher resolution in space and shorter delivery times than are currently in use. Homogeneously reprocessed GNSS data have high potential for monitoring WV climatic trends and variability. With shortening orbit repeat periods, SAR measurements are a new source of information to improve NWP models. Using NWP data within RT processing of GNSS observations can initialize PPP algorithms, shortening convergence times and improving positioning. GNSS signals can be used for L-band remote sensing when Earth-surface reflected signals are considered. GNSS-R contributes to environmental monitoring with estimates of soil moisture, snow depth, ocean wind speed, sea ice concentration and has the potential to be used to retrieve near-surface WV.
We welcome, but not limit, contributions on:
•Estimates of the neutral atmosphere using ground-based and space-based geodetic data, use of those estimates in weather forecasting and climate monitoring
•Multi-GNSS and multi-instruments approaches to retrieve and inter-compare tropospheric parameters
•RT and reprocessed tropospheric products for now-casting, forecasting and climate
•Assimilation of GNSS tropospheric products in NWP and in climate reanalysis
•Production of SAR-based tropospheric parameters and use of them in NWP
•Methods for homogenization of long-term GNSS tropospheric products
•Studies of the delay properties of the GNSS signals for propagation experiments
•Usage of NWP data in GNSS data processing
•Techniques on retrieval of soil moisture from GNSS observations and of ground-atmosphere boundary interactions
•Estimates and methods using GNSS-R for the detection and characterization of sea level and sea ice changes
•Usage of satellite gravity observations for studying the atmospheric water cycle.
This session is also related to the activities of IAG Inter-Commission Committee on "Geodesy for Climate Research".

In this session we search for contributions of general interest within the geodesy community which are not covered by other sessions. The session is open to all branches of geodesy and related fields of research.