G2.3 | Global Geodetic Observing System with a special focus on Earth Rotation
EDI
Global Geodetic Observing System with a special focus on Earth Rotation
Convener: Kosuke Heki | Co-conveners: Florian Seitz, Alberto Escapa, David Salstein, Allison Craddock, Helene WolfECSECS
Orals
| Mon, 24 Apr, 08:30–12:30 (CEST)
 
Room -2.91
Posters on site
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
Hall X2
Posters virtual
| Attendance Mon, 24 Apr, 16:15–18:00 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Mon, 08:30
Mon, 16:15
Mon, 16:15
The Global Geodetic Observing System (GGOS) provides measurements of the gravity, rotation, and shape of the Earth using space and terrestrial geodetic techniques. These measurements must 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 geodesy 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 topics relevant to GGOS, particularly those related to its scientific and social aspects, geodetic infrastructure, observations/products, and activities of services.
This year, a special focus will be reserved to accurate modelling and predictions of Earth rotation.
We are interested in reports on the progress in the theory of Earth rotation as well as in studies that highlight new determinations, analyses, and predictions of Earth Orientation Parameters (EOP), including combinations of different geodetic and astrometric observations for deriving UT1/length-of-day variations and polar motion. We welcome discussions of EOP solutions in conjunction with a consistent determination of terrestrial and celestial frames. We invite contributions investigating the dynamical basis for links between Earth rotation, geophysical fluids, and other geodetic quantities (Earth gravity field, surface deformation...), and explanations for the physical excitations of Earth rotation. Finally, given the relevance of EOP predictions for the operational determination of Earth orientation, we are particularly interested in results from the 2nd EOP Prediction Comparison Campaign and in contributions exploring the potential of innovative techniques, such as the use of artificial intelligence.

Orals: Mon, 24 Apr | Room -2.91

Chairpersons: Martin Sehnal, Helene Wolf, Allison Craddock
08:30–08:35
08:35–08:45
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EGU23-11302
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Highlight
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On-site presentation
Basara Miyahara, Laura Sánchez, Martin Sehnal, and Allison Craddock

The Global Geodetic Observing System (GGOS) is a collaborative contribution of the global Geodesy community to the observation and monitoring of the Earth System. Geodesy is the science of determining the shape of the Earth, its gravity field, and its rotation as functions of time. Essential to reach this goal are stable and consistent geodetic reference frames, which provide the fundamental layer for the determination of time-dependent coordinates of points or objects, and for describing the motion of the Earth in space. With modern instrumentation and analytical techniques, Geodesy is capable of detecting time variations ranging from large and secular scales to very small and transient deformations – all with increasing spatial and temporal resolution, high accuracy, and decreasing latency. The geodetic observational and analysis infrastructures as well as the high-quality geodetic products provide the foundation upon which advances in Earth and planetary system sciences and applications are built. In this way, GGOS endeavors to facilitate and enable production and sharing of the Earth observations needed to monitor, map, and understand changes in the Earth’s shape, rotation, and mass distribution. GGOS also advocates the global geodetic frame of reference as the fundamental backbone for measuring and consistently interpreting global change processes as well as the essential geospatial infrastructure to ensure a homogeneous and sustainable development worldwide.

GGOS closely works with its parent organization, the International Association of Geodesy (IAG), to keep these fundamental geodetic contributions sustainable. The IAG Services provide the infrastructure and products on which all contributions of GGOS are based, and the IAG Commissions and IAG Inter-Commission Committees provide expertise and support to address key scientific issues within GGOS. Additionally, GGOS supports the IAG by strengthening external and interdisciplinary relations and contributions to the broader geospatial information community, including relevant United Nations groups, in particular, the UN Committee of Experts on Global Geospatial Information Management (GGIM), its Subcommittee on Geodesy, and the new UN Global Geodetic Centre of Excellence (scheduled to commence operations in 2023). The main contribution of GGOS in this regard is to support actions and initiatives to communicate the value of Geodesy to society as well as to help to understand and solve complex issues facing the global geodesy community. Towards this objective, GGOS have developed a comprehensive Geodesy portal (https://ggos.org/) including detailed descriptions of geodetic observations (https://ggos.org/obs/) and products (https://ggos.org/products/), and various outreach tools such as short videos to explain the roles and importance of Geodesy to non-geodesists.

How to cite: Miyahara, B., Sánchez, L., Sehnal, M., and Craddock, A.: The Global Geodetic Observing System (GGOS) - infrastructure underpinning Science and Society -, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11302, https://doi.org/10.5194/egusphere-egu23-11302, 2023.

08:45–08:55
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EGU23-6384
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On-site presentation
Kirsten Elger and the GGOS DOI Working Group

The use of digital object identifiers (DOI) for scientific data and scientific software is increasingly common practice for more than a decade. As a result of the Coalition on Publishing Data in the Earth and Space Sciences (COPDESS) and other initiatives, DOI-referenced datasets are fully citable in scholarly literature and more and more journals require the availability of data underlying scientific results and their citation. Technical implementations, like Scholix (a framework for Scholarly Link Exchange) enable direct links and between literature and data and support the visibility of research data. Key elements for enabling these links are persistent identifier (PID). These PIDs allow, e.g., to uniquely identify data, scholarly literature and code (via DOIs), persons (via ORCID), institutions and funding agencies (via ROR – the registry of research organizations), via machine-actionable links and should be included in the DOI metadata.

Similar to other scientific disciplines, the use of DOI for geodetic data is increasing in the last years. While this is easy for static data, like for global of regional gravitational models or GNSS campaign data, most geodetic data are large (mainly due to the large number of files and high temporal resolution) and highly dynamic (real time data acquisition) and highly granular. Geodetic services of the International Association for Geodesy (IAG) are international key player for geodetic data provision and distribution and their operating institutions and funding agencies increasingly require the provision of tangible data use and access statistics. Credit through citation was a major reason for the Global Geodetic Observing System (GGOS) to establish a Working Group on using DOI for geodetic data sets (GGOS DOI WG) and for the working group members.

The GGOS DOI WG was established in 2019 and includes international representatives of IAG Services and geodetic data centres and associated members that aims at developing best practices and recommendations for the consistent implementation of DOIs across all IAG Services and in the greater geodetic community. This presentation will give an update on recent group activities and on the status of DOI minting for geodetic datasets across IAG Services.

How to cite: Elger, K. and the GGOS DOI Working Group: The world of DOIs for geodetic data – metadata recommendations and status report of the GGOS DOI Working Group, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6384, https://doi.org/10.5194/egusphere-egu23-6384, 2023.

08:55–09:05
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EGU23-1539
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On-site presentation
Cornelis Slobbe, Martin Verlaan, Roland Klees, and Yosra Afrasteh

Water levels from hydrodynamic models typically lack an absolute vertical reference, and can thus not be linked directly to digital elevation models to assess coastal floodrisks. Instead, most workarounds rely on tide gauges that are connected to the land-based vertical reference to establish this link. The lack of an absolute vertical reference also makes it impossible to directly assimilate observed total water levels into models as this requires both observed and modeled water levels to refer to the same vertical datum.

The first consequence underlines the urgency of realizing an international height reference system that is easily accessible to users and which is adopted as the vertical reference in global tide gauge datasets and digital terrain models. Indeed, the lack of such an international height reference frame makes it impossible to accurately determine the impact and risks of sea level rise and changes in extreme water levels due to climate change. Let alone that an agenda for adaptation measures can be drawn up. The second consequence limits the accuracy of modeled water levels as existing workarounds do not exploit the observed long-term mean water level variations. At the same time, the assimilation of total water levels imposes strong requirements to the accuracy of an international height reference frame. Hydrodynamic models are extremely sensitive to slopes in observed water levels. Even small erroneous slopes between tide gauges introduced by errors in the vertical referencing, impose false currents that in turn result in model instabilities.

In turn, hydrodynamic models offer great and unique opportunities to assist in the realization of an international height reference system. The difference between the observation-derived mean water level (MWL) at location B and the sum of the observation-derived MWL at location A and the model-derived mean water level difference between the two locations is a proxy for the datum shift between the height datums used at locations A and B. The asset and uniqueness of the technique referred to as ‘model-based hydrodynamic leveling’ lies in the fact that it allows to transfer a height datum over large water bodies without the need to acquire new measurements. In the Dutch Versatile Hydrodynamics project, we implemented the technique and combined the data with geopotential differences from spirit leveling/gravimetry to compute a new realization of the European Vertical Reference System (EVRS).

This presentation will i) explain and demonstrate the need for an international height reference system from the perspective of hydrodynamic modelers; ii) demonstrate the potential contribution of hydrodynamic models to the realization of such a height system using the results obtained in the Versatile Hydrodynamics project, and iii) outlines ideas for future work.

How to cite: Slobbe, C., Verlaan, M., Klees, R., and Afrasteh, Y.: Hydrodynamic modeling and the realization of an international height reference system - urgent need and potential contribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1539, https://doi.org/10.5194/egusphere-egu23-1539, 2023.

09:05–09:20
09:20–09:30
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EGU23-13216
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ECS
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On-site presentation
Alexander Kehm, Laura Sánchez, Mathis Bloßfeld, Manuela Seitz, Hermann Drewes, Detlef Angermann, and Florian Seitz

High-resolution regional applications require regional reference frames with dense networks of reference stations. These regional reference frames can be realised in the form of multi-year reference frames (that can be fixed to a specific tectonic plate like EUREF for Europe) or as epoch reference frames to represent non-linear phenomena such as earthquakes or loading effects (like SIRGAS for Latin America). Common to these realisations is that they are based on GNSS networks with a geodetic datum that is realised by alignment to the global reference frame (ITRF or IGS TRF).

In consequence, the origin of these networks reflects the Earth’s centre of figure rather than the Earth’s instantaneous centre of mass. Moreover, the quality of the realised datum decreases over time, as the linearly-parameterised coordinates of the global reference frame have to be extrapolated beyond the observation period. These effects mean a significantly reduced value of station-specific displacement time series for the study of, e.g., local geophysical effects.

This study presents an alternative approach for the realisation of a regional epoch reference frame for Latin America. The approach is based on the common weekly solution of global SLR, VLBI and GNSS networks combined at the normal equation level. Thereby, SLR determines the origin, SLR and VLBI jointly determine the scale, and a homogeneously distributed global GNSS network is used to realise the orientation. This GNSS network is densified by the stations of the regional sub-network, namely the stations of the Latin American SIRGAS network. The approach does not necessarily rely on fiducial points in the region of interest, which means that it is conceptually transferrable to other regional networks.

In order to cope with system-specific deficiencies of SLR and VLBI, namely data gaps, low station performances and frequently changing observational networks deteriorating the realised datum parameters, we propose a strategy to stabilise the realised datum via filtering the input data of these techniques at the normal equation level before combination with GNSS.

We evaluate the realised datum of the epoch-wise weekly solutions by comparison against the ITRF2014 as an independent multi-year realisation of the ITRS and against the JTRF2014 as an independent sub-secular realisation of the ITRS. Moreover, station-specific displacement time series are validated against non-tidal loading displacement time series derived from geophysical fluid models provided by ESMGFZ in order to demonstrate that the displacement time series reflect seasonal geophysical processes in a geocentric frame.

How to cite: Kehm, A., Sánchez, L., Bloßfeld, M., Seitz, M., Drewes, H., Angermann, D., and Seitz, F.: Combination strategy for regional geocentric epoch reference frames, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13216, https://doi.org/10.5194/egusphere-egu23-13216, 2023.

09:30–09:40
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EGU23-8078
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On-site presentation
Jakob Flury, Igor Koch, and Mathias Duwe

From the investigation of GRACE and GRACE-FO instrument data, we are aware of quite a number of unmodeled effects and deficiencies in the calibration of instruments. We want to use these deficiencies as an example to discuss how for a core GGOS observation technique, such as GRACE / GRACE-FO, all opportunities to assess and improve sensor calibration and to identify and characterize unmodeled effects affecting the measurements should be explored. This may seem obvious, but we will show that a major effort on this field would be very desirable. We deliberately choose the GGOS session for a broader discussion of the topic, and we want to highlight the importance of an overarching approach that combines insight from different satellite missions and space techniques.

How to cite: Flury, J., Koch, I., and Duwe, M.: Well calibrated space sensor systems for GGOS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8078, https://doi.org/10.5194/egusphere-egu23-8078, 2023.

09:40–09:50
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EGU23-15885
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On-site presentation
Laurent Soudarin, Frank Lemoine, and Arnaud Sellé

On 1 July 2023, the International DORIS Service (IDS) will celebrate the 20th anniversary of its creation under the umbrella of the International Association of Geodesy (IAG). The IDS was established to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associated Analysis Center, a Combination Center, and several partner groups.

The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 32 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system, ... Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF. This year, a 9th satellite joins the current constellation of DORIS satellites. It is SWOT, launched on 16 December 2022. Never before have so many DORIS instruments been in operation simultaneously.

This presentation addresses the recent achievements made by IDS and its components, and the future plans of the service.

How to cite: Soudarin, L., Lemoine, F., and Sellé, A.: The International DORIS Service: almost 20 years old., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15885, https://doi.org/10.5194/egusphere-egu23-15885, 2023.

09:50–10:00
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EGU23-12103
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ECS
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Virtual presentation
Shuang Zhao and Yusuke Yokota

As the unique approach to obtain centimeter-level seafloor positioning information, Global Navigation Satellite System-Acoustic ranging combination technique (GNSS-A) (Spiess, 1985) has drawn increasing attention and plays an important role in ocean engineering and marine geoscience research (Gagnon et al. 2005; Tadokoro et al. 2006; Watanabe et al.2014; Yokota et al. 2016; Yang et al. 2018).

GNSS-A positioning accuracy is significantly restricted by temporal and spatial variation errors related to propagation velocity of acoustic signals, the bridge medium to connect sea-surface platform and seafloor stations. Valuable investigations focusing on sound speed structure (SSS) modelling and inversion have been released and contribute to the GNSS-A performance improvements (Fujita et al. 2006; Ikuta et al. 2008; Honsho et al. 2017; Yokota et al. 2019; Watanabe et al. 2020; Yang et al. 2020; Yokota et al, 2022; Xue et al. 2023, in prep). It’s promising to progressively suppress SSS errors effect on seafloor positioning capability based on the increasingly refined SSS model policy.

Besides concentration on SSS errors modeling and corrections, additional consideration of positional uncertainty of sea-surface platform, one of vital parts of entire GNSS-A observation system, is reasonable for refined seafloor positioning policy. Currently, joint/total adjustment model and parameter estimation of the transducer and seafloor transponder for underwater precise point positioning have been published (Zhao et al. 2021). Furthermore, for seafloor geodetic network scene, numerical tests considering the positional uncertainty of sea-surface transducer were conducted. Further research may be hopeful to evaluate and control error propagation effect on seafloor positioning from sea-surface segment and helpful for usage of more flexible platform.

How to cite: Zhao, S. and Yokota, Y.: Consideration of positional uncertainty of sea-surface platform for GNSS-A seafloor positioning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12103, https://doi.org/10.5194/egusphere-egu23-12103, 2023.

10:00–10:15
Coffee break
Chairpersons: Florian Seitz, Alberto Escapa, David Salstein
10:45–10:50
10:50–11:00
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EGU23-14052
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ECS
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On-site presentation
Justyna Śliwińska, Tomasz Kur, Jolanta Nastula, Małgorzata Wińska, Henryk Dobslaw, and Aleksander Partyka and the 2nd EOP PCC Participants

The accurate determination of Earth Orientation Parameters (EOP) requires post-processing of observational data collected from various space geodetic techniques, which causes delays in providing EOP solutions. However, receiving instantaneous information about EOP in real time is crucial in precise positioning and navigation. Therefore, EOP prediction (particularly short-term) has become a subject of increased attention within the international geodetic community.

In the light of the developments of advanced geodetic data processing, modelling effective angular momentum functions, and developing new prediction methods, a re-assessment of the various EOP predictions was pursued in the frame of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC). The campaign was run by Centrum Badań Kosmicznych Polskiej Akademii Nauk (CBK PAN), in cooperation with GeoForschungsZentrum (GFZ) and under the auspices of the International Earth Rotation and Reference Systems Service (IERS). The campaign started on 1st September 2021 and finished on 28th December 2022, giving 7327 submitted predictions within 82 weeks. The campaign was a great success of the geodetic community thanks to international cooperation.

The presentation provides the summary of the 2nd EOP PCC. We focus on the recap of the statistics on the involved participants, i.e., the number of prediction methods and input data. Then we will present the accuracy of EOP predictions based on the mean absolute error computed for IERS 14 C04 solution as a reference. Additionally, we present the quality of predictions in clusters created from the campaign participants (IDs) based on their modern prediction methods combined with input data (EOP observations and data on the Earth’s surficial fluids) We conclude the presentations with plans for the prediction assessment, also in terms of the possible continuation of the campaign involving new release of IERS C04 20.

How to cite: Śliwińska, J., Kur, T., Nastula, J., Wińska, M., Dobslaw, H., and Partyka, A. and the 2nd EOP PCC Participants: Achievements of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14052, https://doi.org/10.5194/egusphere-egu23-14052, 2023.

11:00–11:10
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EGU23-3090
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On-site presentation
Robert Dill and Henryk Dobslaw

Time-variations in the orientation of the solid Earth are largely governed by the exchange of angular momentum with the surface geophysical fluids of atmosphere, oceans, and the land surface. Modelled fields of atmospheric winds, atmospheric surface pressure, ocean currents, ocean bottom pressure, and terrestrial water storage allow to calculate effective angular momentum (EAM) functions that provide highly reliable information about the orientation changes of the Earth. EAM forecasts derived from model forecast runs support substantially short-term Earth Orientation Parameters (EOP) Predictions. So far, routinely available EAM forecasts do not include any error information needed for rigorous combination of EAM forecasts with EOP predictions from various geodetic techniques. Based on hindcast experiments, we analysed the EAM forecast error and trained a neural network to predict EAM forecast errors. As expected, EAM forecast errors increase with the prediction horizon but we found also irregular large variation in the EAM forecast error that seem to be well predictable with machine learning methods. 

How to cite: Dill, R. and Dobslaw, H.: Predicting Effective Angular Momentum Function Forecast Errors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3090, https://doi.org/10.5194/egusphere-egu23-3090, 2023.

11:10–11:20
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EGU23-14827
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ECS
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On-site presentation
Sadegh Modiri, Daniela Thaller, Lisa Klemm, Daniel König, Hendrik Hellmers, Sabine Bachmann, Claudia Flohrer, and Anastasiia Walenta

Variations in Earth orientation parameters (EOP) are related to mass redistribution, gravitational, and geodynamic processes in the Earth system and have gained a great deal of attention in Earth science, astronomy, and climate change studies. In addition, real-time EOP information is needed for many space geodetic applications, including satellite navigation from the ground and low-Earth orbit, like tracking interplanetary spacecraft and forecasting the weather. Currently, the EOP can be estimated at the best possible accuracy with modern high-precision space geodetic techniques like Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), and Satellite Laser Ranging (SLR). However, the complex nature of data processing and the time it takes to process it always lead to delays. Consequently, predicting EOP is of great scientific and practical importance. Accordingly, several methods have been developed and applied to EOP prediction. In spite of this, the accuracy of EOP still needs to meet our expectations, even for forecasts of a few days into the future. We will therefore have to face two major challenges in order to provide the best prediction data: which input data to use and which prediction methods are superior to others. In order to answer these two questions, new methods or a combination of existing approaches are investigated to improve the accuracy of the predicted EOP time seires. Such in-depth investigations are currently conducted within the “Second EOP Prediction Comparison Campaign (EOP-PCC)” organized by IAG and IERS. In this study, we investigate a redesigned prediction package (input data and method) to improve the possibility of bridging the existing gap between the observation and the final estimated product.

We will briefly present our contribution to EOP-PCC and illustrate the result of EOP data obtained from single space geodetic techniques provided by the department of geodesy at BKG. Then, we run our prediction algorithm with the official IERS EOP series and our BKG’s single-technique analysis products for VLBI and SLR using the combination of a deterministic and a stochastic method and compare it with different prediction techniques. Finally, we will show the potential of using a combination of VLBI and GNSS techniques to obtain real-time EOP estimates.

How to cite: Modiri, S., Thaller, D., Klemm, L., König, D., Hellmers, H., Bachmann, S., Flohrer, C., and Walenta, A.: EOP Prediction with special focus on using EOP products by different space geodetic techniques as input, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14827, https://doi.org/10.5194/egusphere-egu23-14827, 2023.

11:20–11:30
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EGU23-6737
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ECS
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On-site presentation
Sonia Guessoum, Santiago Belda, José Manuel Ferrándiz, Sadegh Modiri, Robert Heinkelmann, Harald Schuh, and Sujata Dhar

Polar Motion is the movement of the Earth's rotational axis relative to its crust, reflecting the influence of the material exchange and mess redistribution of each layer of the Earth on the Earth's rotation axis.
The real-time estimation of Polar Motion (PM) is needed for the navigation of Earth satellites and interplanetary spacecraft. However, it is impossible to have real-time information due to the complexity of the measurement model and data processing.

Various prediction methods have been developed. However, the accuracy of PM prediction is still not satisfactory even for a few days in the future. Therefore, a new technique or a combination of the existing methods needs to be investigated for improving the accuracy of the prediction PM.
In this study, we combine the 1D  Convolutional Neural Network with the Singular Spectrum Analysis (SSA).
 The computational strategy follows multiple steps, first, we model the predominant trend of the PM time series using SSA. Then, the difference between the PM time series and its SSA estimation is modeled using the 1D Convolution Neural Network. However, we developed a Multivariate Multi step 1D-CNN Model with a Multi-output strategy to predict at the same time both components (Xp, Yp)  of the PM.  . We introduce to the  Model: the Ocean Angular Momentum, Atmospheric Angular Momentum, and Hydrological Angular Momentum (OAM+AAM+HAM) to improve the results. Multiple sets of PM predictions which range between 1 and 10 days have been performed based on an IERS 14 C04 time series to assess the capability of our hybrid Model. Our results illustrate that the proposed method can efficiently predict both (Xp, Yp) of PM.

How to cite: Guessoum, S., Belda, S., Ferrándiz, J. M., Modiri, S., Heinkelmann, R., Schuh, H., and Dhar, S.: The short-term prediction of Polar Motion using the combination of SSA and the Multivariate Multi-step 1D- Convolutional Neural Networks with Multioutput strategy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6737, https://doi.org/10.5194/egusphere-egu23-6737, 2023.

11:30–11:45
11:45–11:55
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EGU23-3469
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On-site presentation
Richard Gross, Claudio Abbondanza, Mike Chin, Mike Heflin, and Jay Parker

Earth orientation parameters (EOPs) are currently determined from measurements taken by the space-geodetic techniques of SLR, VLBI, GNSS, and DORIS. But each technique has its own unique strengths and weaknesses in this regard. Not only is each technique sensitive to a different subset and/or linear combination of the EOPs, but the averaging time for their determination is different, as is the interval between observations, the precision with which they can be determined, and the duration of the resulting EOP series. By combining the individual series determined by each technique, a series of the Earth's orientation can be obtained that is based upon independent measurements and that spans the greatest possible time interval. Such a combined Earth orientation series is useful for a number of purposes, including a variety of scientific studies and as an a priori series for use in data reduction procedures. However, care must be taken in generating such a combined series in order to account for differences in the underlying reference frames within which each individual series is determined (which can lead to differences in the bias and rate of the Earth orientation series). Traditionally, differences in the underlying reference frames are accounted for by applying a correction to the bias and rate of each individual series being combined with the goal of placing the series within a common reference frame. But there is an uncertainty associated with estimating the bias and rate correction that needs to be applied to each series. In fact, this uncertainty is a major (if not the major) source of error in combined EOP series. However, this source of error can be mitigated by jointly combining the EOP series with the terrestrial reference frame. Recent ITRF and JTRF solutions such as ITRF2020 and JTRF2020 have included EOP series in their determination. In this presentation, the ITRF2020 and JTRF2020 combined polar motion series will be compared to the more traditionally determined IERS Bulletin A and JPL KEOF (Kalman Earth Orientation Filter) combined polar motion series in order to study the improvement attained by jointly determining the combined EOP series with the terrestrial reference frame.

How to cite: Gross, R., Abbondanza, C., Chin, M., Heflin, M., and Parker, J.: Improving Combined EOP Series by Jointly Determining Them with the Terrestrial Reference Frame, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3469, https://doi.org/10.5194/egusphere-egu23-3469, 2023.

11:55–12:05
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EGU23-4162
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ECS
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On-site presentation
Mostafa Kiani Shahvandi, Robert Dill, Henryk Dobslaw, Siddhartha Mishra, and Benedikt Soja

Determination of Earth Orientation Parameters (EOP) with utmost accuracy requires the combination of various data sources from different space geodetic techniques, some of which requiring long processing time. This results in a latency of up to several weeks by which the so-called final EOP are released. Since some of the important applications, including satellite navigation and orientation of deep space telescopes, require instantaneous EOP information, the so-called rapid determination and also prediction of EOP are needed. International Earth Rotation and Reference Systems Service (IERS) provides rapid EOP by using the most recent Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) 24-hour and intensive sessions data. However, there are some discrepancies between these rapid data and the final, most accurate EOP. In order to reduce these discrepancies and achieve more accurate rapid EOP, we focus on applying machine learning algorithms for polar motion components (xp, yp) and dUT1=UT1-UTC. We focus on a window of 63 days with 31 day predictions to the past and 31 day predictions to the future.

We devise a new algorithm called ResLearner, which is a machine learning method based on multilayer perceptrons trying to learn the differences between rapid and final EOP data. We use informative features such as Effective Angular Momentum (EAM) data (both the observations provided by GFZ and the 14-day forecasts provided by ETH Zurich), tides, Liouville equation for (xp, yp), and a linear relation between dUT1 and the axial components of EAM.
We use ResLearner in the context of Deep Ensembles in order to derive the uncertainty in the estimations. We also address the so-called unmixing and self-calibration problems. The former enables us to unravel the causes behind the discrepancies between rapid and final EOP as provided by IERS, while the latter could help us reduce these erroneous effects. 

We train the algorithms on both the IERS and Jet Propulsion Laboratory (JPL) final EOP data. Our ResLearner method can consistently reduce the discrepancies between rapid and final EOP across all days. The improvement in accuracy is up to 55%. We observe some unexpected behaviour related to day 0 of prediction, in which the accuracy of the IERS is significantly better than the immediately preceding or following values. Our unmixing algorithm shows that this behaviour is probably related to erroneous, non-linear effects of EAM at day 0, and also semi-diurnal, diurnal, long-period retrograde and prograde, and zonal tides. Using our self-calibration algorithm for EAM, we can slightly improve the prediction performance by up to 14%.

Finally, we provide the improved rapid EOP data publicly, operationally, and on a daily basis, on the ETH Zurich prediction center website at https://gpc.ethz.ch/EOP/Rapid/

How to cite: Kiani Shahvandi, M., Dill, R., Dobslaw, H., Mishra, S., and Soja, B.: Improving the accuracy of rapid Earth Orientation Parameters with the "ResLearner" machine learning method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4162, https://doi.org/10.5194/egusphere-egu23-4162, 2023.

12:05–12:15
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EGU23-8821
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On-site presentation
José M. Ferrándiz, Maria Karbon, Santiago Belda, and Alberto Escapa

The derivation and subsequent use of suitable corrections to the current IAU2006/IAU2000 precession/nutation models is a main objective of the IAU/IAG Joint Working Group on Improving theories and models of the Earth rotation (JWG ITMER). It has been recognized in the latter IERS/GGOS Unified Analysis Workshops as the fastest way of improving the accuracy of those models at the short-term and thus contributing to the development of the last Resolutions of the IAG and IAU on Earth rotation.

In the last few years, some research groups have proposed different sets of corrections or updates to precession and either the forced or free nutations – including alternative approaches to free core nutation (FCN) models. The derivations of the various sets are related to VLBI solutions or observational data to quite different extents. The purpose of this study is providing a wider view into the performance of such corrections, focusing on features and capabilities more directly related to VLBI data analysis

How to cite: Ferrándiz, J. M., Karbon, M., Belda, S., and Escapa, A.: On the performance of the corrections to the current precession-nutation models in VLBI data analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8821, https://doi.org/10.5194/egusphere-egu23-8821, 2023.

12:15–12:30

Posters on site: Mon, 24 Apr, 16:15–18:00 | Hall X2

Chairpersons: Kosuke Heki, Florian Seitz
GGOS
X2.32
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EGU23-1281
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Highlight
Martin Sehnal, Laura Sánchez, Detlef Angermann, Allison Craddock, and Basara Miyahara

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) is a collaborative contribution of the global geodesy community to the observation and monitoring of the Earth System. Geodetic observation techniques and analysis infrastructures, as well as the high-quality geodetic products, provide the foundation upon which advances in Earth and planetary system sciences and applications are built.

One main objective of GGOS is to support actions and initiatives to communicate the value of Geodesy to society, as well as help to understand and solve complex issues facing the global geodetic community. Towards this objective, GGOS has completely redesigned its website, www.ggos.org, which serves as a “point of entry to geodesy” to facilitate discoverability and usability of geodetic data and products. This includes explanations about: IAG services, geodetic observations and geodetic products. With this, GGOS engages with diverse user communities to increase awareness of geodesy and the ever-expanding benefits of geodesy in every-day applications.

In addition, GGOS recently produced short videos to explain the applications and importance of geodesy to non-geodesists. The new “Discover GGOS and Geodesy” video is available on YouTube in multiple languages.

How to cite: Sehnal, M., Sánchez, L., Angermann, D., Craddock, A., and Miyahara, B.: GGOS’s Geodetic Information Portal: Linking Geodesy and Society, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1281, https://doi.org/10.5194/egusphere-egu23-1281, 2023.

X2.33
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EGU23-13114
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Detlef Angermann, Thomas Gruber, Michael Gerstl, Robert Heinkelmann, Urs Hugentobler, Laura Sanchez, and Peter Steigenberger

The Bureau of Products and Standards (BPS) is a key component of the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG). It supports GGOS in its goal to provide consistent geodetic products needed to monitor, map, and understand changes in the Earth’s shape, rotation, and gravity field. In its current structure, the Committees “Contributions to Earth System Modeling” and “Definition of Essential Geodetic Variables” as well as the Working Group “Towards a consistent set of parameters for the definition of a new Geodetic Reference System (GRS)” are associated to the BPS.

This poster contribution presents the role of the BPS and it highlights some of the recent activities, which are focused on the updating of the IERS Conventions, mainly related to Chapter 1 "General definitions and numerical standards", the updating of the BPS inventory of standards and conventions used for the generation of IAG products to incorporate the latest developments in the field, the compilation of user-friendly descriptions of geodetic products published at the GGOS website, and the contribution to GGOS films for specific products. The BPS activities also comprise the interaction with IAG and other entities in the field of standards and conventions, such as the IAG Services, the IERS Conventions Center, the Commission A3 “Fundamental Standards” of the International Astronomical Union (IAU), ISO/TC 211 and the Working Group ``Data Sharing and Development of Geodetic Standards” of the UN-GGIM Subcommittee on Geodesy (SCoG).

How to cite: Angermann, D., Gruber, T., Gerstl, M., Heinkelmann, R., Hugentobler, U., Sanchez, L., and Steigenberger, P.: Role and Activities of the GGOS Bureau of Products and Standards, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13114, https://doi.org/10.5194/egusphere-egu23-13114, 2023.

X2.34
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EGU23-12049
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Highlight
Laura Sanchez, Jianliang Huang, Riccardo Barzaghi, and Georgios S. Vergos

Measuring, studying, and understanding global change effects demand unified geodetic reference frames with (i) an order of accuracy higher than the magnitude of the effects to be observed, (ii) consistency and reliability worldwide, and (iii) long-term stability. The development of the International Terrestrial Reference System (ITRS) and its realisation, the International Terrestrial Reference Frame (ITRF), enable the precise description of the Earth’s geometry by means of geocentric Cartesian coordinates with an accuracy at the cm-level and with global consistency. An equivalent high-precise global height reference system that provides the basis for the consistent determination of gravity field-related coordinates worldwide, in particular geopotential differences or physical heights, is missing. Without a conventional global height system, most countries rely on local height systems, which have been implemented individually, applying in general non-standardised and non-uniform procedures. It is proven that their combination in a global frame presents discrepancies at the metre level. Therefore, a core objective of the international geodetic community is to establish an international standard for the precise determination of physical heights. This standard is known as the International Height Reference System (IHRS). Its realisation has been a main topic of research during the last years. Recent achievements concentrate on (1) compiling detailed standards, conventions, and guidelines for the IHRS realisation, (2) evaluating computational approaches for the consistent determination of potential differences, and (3) designing an operational infrastructure that ensures the maintenance and long-term stability of the IHRS and its realization. This contribution summarises advances and current challenges in the establishment, realization and sustainability of the IHRS.

How to cite: Sanchez, L., Huang, J., Barzaghi, R., and Vergos, G. S.: Advances in the determination of a global unified reference frame for physical heights, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12049, https://doi.org/10.5194/egusphere-egu23-12049, 2023.

Earth Rotation
X2.35
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EGU23-12366
Małgorzata Wińska, Justyna Śliwińska, and Jolanta Nastula

The motion of the Earth's pole is excited by processes internal to the Earth's system – continually changing mass distribution in the geophysical fluids, i.e., atmosphere, ocean, and land hydrology. The mass redistribution and its movements within the Earth system excite the Earth's rotational changes mainly at seasonal or shorter timescales. The importance of atmospheric and oceanic angular momentum (AAM, and OAM, respectively) signals for polar motion excitation at seasonal and interannual timescales is well known. However, previous studies showed that the AAM, computed from different models of atmospheric pressure changes and winds, slightly differ from each other, especially in ­χ1 component. The discrepancies between various representations of ocean bottom pressure and currents from different OAM models are apparent too.

An essential technique for understanding Earth's rotational changes is comparing the sum of mass and motion terms of AAM and OAM based on different geophysical models.

Up to now, studies of geophysical excitations of polar motion containing AAM, OAM, and hydrological angular momentum (HAM) have not achieved entire agreement between geophysical (sum of AAM, OAM, and HAM obtained from the models) and geodetic (GAM, geodetic angular momentum; obtained from geodetic measurements of polar motion) excitation. There are many geophysical models of the atmosphere, oceans, and land hydrology that can be used to compute polar motion excitation. However, these models are very complex and still suffer from uncertainties in the process descriptions, parametrization, and forcing.

Until now, no studies have shown that selecting one particular combination of AAM+OAM models provides the best correlation with GAM. The choice of AAM and OAM time series is usually entirely arbitrary and the only criterion considered is that the AAM model should be combined with the OAM model in which the forcing data is taken from the  AAM model used. 

This analysis of the most recent AAM and OAM series highlights that hydrological signals in polar motion differ significantly. The main goal of this presentation is to demonstrate that using different combinations of mass and motion terms of both AAM and OAM may have a considerable influence on the geophysical excitation of polar motion and its consistency with GAM. In this study, we extend the present understanding of the problem of inconsistency of mass and especially motion terms of different AAM and OAM models at seasonal and non-seasonal time scales.

How to cite: Wińska, M., Śliwińska, J., and Nastula, J.: Comparison between polar motion excitation functions estimated from different models of geophysical fluids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12366, https://doi.org/10.5194/egusphere-egu23-12366, 2023.

X2.36
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EGU23-14040
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Sigrid Böhm and David Salstein

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides, amongst others, the Earth climate response to several different scenarios that simulate possible future anthropogenic drivers of climate change. The scenarios are characterized by different forcings, which are defined from a combination of plausible future societal developments, the Shared Socioeconomic Pathways (SSPs), and the Representative Concentration Pathways (RCPs), identified by the approximate radiative forcing level anticipated for 2100.

In a previous work, we investigated length of day variations induced by multi-model projections of zonal wind fields, stemming from historical simulations and from the four scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. In order to cover the same set of five scenarios that are treated in the sixth assessment report of the Intergovernmental Panel on Climate Change, we add another low emission scenario, SSP1-1.9, in this follow-up study. Furthermore, we do not only assess the wind term but complete the analysis with the calculation of the respective atmospheric surface pressure terms. We are especially interested in the long-term variations and trends of length of day predicted for the period from 2015-2100 and the connection with variations and trends of the global surface temperature patterns. Regarding the excitation by zonal winds, preliminary assessments show that higher emission scenarios, which are associated with more intense global warming, would lead to a moderate increase in atmospheric angular momentum and thus to a proportional decrease of the Earth rotation rate.

How to cite: Böhm, S. and Salstein, D.: Atmospheric excitation of length of day inferred from 21st century climate model projections, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14040, https://doi.org/10.5194/egusphere-egu23-14040, 2023.

X2.37
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EGU23-13073
Lisa Klemm, Daniela Thaller, Claudia Flohrer, Anastasiia Walenta, Dieter Ullrich, and Hendrik Hellmers

We present BKG´s current activities in the area of combined data processing of different space-geodetic techniques. The primary goal of the combined analyses is the improvement of the consistency between the techniques through common parameters, mainly Earth Rotation Parameters (ERP), and thereby to improve also the resulting ERP. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP time series with latencies of about 1-2 or 14 days, depending on the input data we used. In this way, we achieved a significant improvement in accuracy, especially for the dUT1 series, compared to the individual technique-specific solutions. The processing is based on homogenized datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level.

Our main objective is to generate an ERP product that is characterized by a continuous, daily and regular resolution and the shortest possible latency, especially for the highly variable dUT1. The mandatory requirement for achieving these characteristics is the rapid availability of the input data on the daily basis, especially of the VLBI Intensive sessions. The time series of daily SINEX files of the legacy (S/X) VLBI Intensive sessions show some gaps in the past. The reasons for this are manifold and can be found throughout the entire VLBI processing chain, i.e., from the observation, i.e. station ability to participate, to the analysis, i.e. the data quality revision. However, in the last two years, an increasing number of VGOS Intensive campaigns has been conducted in addition to the legacy Intensives. As a result, the Intensive series is nowadays almost without gaps and there are even more than one Intensive sessions (up to 6) available per day. In our recent studies, we compare the VGOS and legacy Intensives data in terms of their latency and the quality of the resulting dUT1 estimates and integrate them into our combination process. We highlight also the challenges of extending the combination with the new VGOS data. Its incorporation will eventually pave the way for establishing an operational ERP product at BKG.

How to cite: Klemm, L., Thaller, D., Flohrer, C., Walenta, A., Ullrich, D., and Hellmers, H.: Improving the temporal regularity and continuity of consistently combined ERP: A closer look at today’s VLBI Intensives., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13073, https://doi.org/10.5194/egusphere-egu23-13073, 2023.

X2.38
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EGU23-13472
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ECS
Aleksander Partyka, Justyna Śliwińska, Tomasz Kur, Jolanta Nastula, Henryk Dobslaw, and Małgorzata Wińska and the 2nd EOP PCC Participants

Earth Orientation Parameters (EOP) represent the rotational part of the transformation between the current releases of the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF). The determination of EOPs requires post-processing of observational data collected from various space geodetic techniques, which causes some delays in the provision of EOP solutions.

In the light of the developments in the field of advanced geodetic data processing, modelling effective angular momentum functions and developing new prediction methods, a re-assessment of the various EOP predictions is currently pursued in the frame of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC). The campaign started in September 2021 and its main part finished on 28 December 2022. It was run by the Centrum Badań Kosmicznych Polskiej Akademii Nauk in cooperation with GeoForschungsZentrum and under the auspices of the International Earth Rotation and Reference Systems Service (IERS).

In this presentation, we provide initial analysis of the impact of the choice of reference series used on the assessment of predictions submitted to the 2nd EOP PCC. We will compare the single-technique EOP series provided by International Global Navigation Satellite Systems Service (IGS), International Laser Ranging Service (ILRS), International Very Long Baseline Interferometry Service (IVS) as well as selected combined series with reference to official IERS solutions (IERS 14C04) for respective EOPs. We also look closer to the input data exploited by campaign participants to process predictions by dividing them into subclasses. We conduct selected statistical analyses, including forecast horizons, to show variabilities caused by reference series. We also analyse the number of rejected predictions with use of beta parameter considering various references. Finally, we focus on Mean Absolute Error (MAE) computed for 10 days and 30 days of predictions to discuss potential effects triggered by the input data choice. This work concludes with potential impacts of the input EOP data on the accuracy of the received EOP predictions.

How to cite: Partyka, A., Śliwińska, J., Kur, T., Nastula, J., Dobslaw, H., and Wińska, M. and the 2nd EOP PCC Participants: Impact of the reference series choice in analysis of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC) results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13472, https://doi.org/10.5194/egusphere-egu23-13472, 2023.

X2.39
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EGU23-10034
Santiago Belda, Maria Karbon, Alberto Escapa, Víctor Puente, Sadegh Modiri, and José M. Ferrándiz

Consideration of the Free Core Nutation (FCN) is required to improve the modelling of the Celestial Pole Offsets (CPO) since it is the major source of inaccuracy or unexplained time variability with respect to the current IAU2000 nutation theory. The FCN is a free mode related to the non-alignment of the rotation axis of the core and of the mantle. It can only be measured/detected by Very Long Baseline Interferometry (VLBI). IERS Conventions (2010) recommends an empirical FCN model of Lambert (2007). However, other alternative models are available today (e.g. Krásná et al. 2013; Malkin 2013; Belda 2016). All these models are based on the sliding window least-squares fit method, assuming a constant period of about -430 solar days.

In our previous studies, we evidenced that the period of the FCN could vary with time. Due to this FCN period variability, the conventional empirical FCN models would not be completely correct. Therefore, should we find out new mathematical approaches/strategies to model the FCN?

In this study, a new mathematical strategy is examined. We utilized the Whittaker smoother to extract the desired signal from the CPO series obtained from VLBI. This technique tends to behave as highly adaptive and versatile fitting algorithms and can thus replace conventional FCN models. Apart from that, it is extremely fast, gives continuous control over smoothness with only one parameter (lambda), interpolates automatically, and allows fast leave-one-out cross-validation. The preliminary assessment using the observed nutations derived from VLBI analysis demonstrated the potential of Whitaker smoother as an optimum algorithm to successfully reconstruct the FCN signal with more efficient performance to retrieve reliable patterns. This analysis could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS).

How to cite: Belda, S., Karbon, M., Escapa, A., Puente, V., Modiri, S., and Ferrándiz, J. M.: Should we find out new mathematical strategies to model the Free Core Nutation?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10034, https://doi.org/10.5194/egusphere-egu23-10034, 2023.

Posters virtual: Mon, 24 Apr, 16:15–18:00 | vHall GMPV/G/GD/SM

Chairpersons: Kosuke Heki, Florian Seitz
vGGGS.3
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EGU23-16405
Any new Geodetic Reference System should be mean-tide
(withdrawn)
Jaakko Mäkinen
vGGGS.4
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EGU23-2983
Ryuichi Ichikawa, Hidekazu Hachisu, Mamoru Sekido, Tetsuya Ido, Yoshifumi Hiraoka, Eiichirou Harima, Shuntaro Fukaya, Masahiro Nakashima, Koji Matsuo, Yuichi Aoyama, Akihisa Hattori, and Yoichi Fukuda

The frequency accuracy of optical atomic clocks has dramatically increased over the past 15 years, improving by more than two orders of magnitude from 16 digits of precision to 18 or even 19 digits of precision. Since around 2015 researchers from around the world began to consider a redefinition of the second that uses optical atomic clocks. Since then, the development of optical atomic clocks has progressed and the recent results demonstrated to detect the frequency change with 18 digits of precision.

The National Institute of Information and Communications Technology (NICT) has developed the Sr optical lattice clock and optical ion clocks employing In+ and Ca+, as well as a Sr optical lattice clock that provides calibration data to BIPM. On the other hand, the centimeter-level uncertainty of site elevation has caused 10-18-level frequency uncertainties of optical frequency standards. Therefore, it is significantly important to understand frequency changes caused by solid-earth tides that often range from 10 to 20 cm in amplitude, by oceanic tidal loading, crustal deformations due to earthquakes, and ground movements with groundwater changes for the stable operation of optical atomic clocks.

NICT, in collaboration with partners including the Geospatial Information Authority of Japan (GSI), has begun observations and data analysis to evaluate how these effects interact with optical atomic clocks. Since early 2021, NICT and GSI have been jointly conducting leveling surveys and relative gravimeter observations at NICT’s headquarters in Koganei. These observations reduce the contribution of gravitational redshift to the total uncertainty of the NICT-Sr1 optical lattice clock has been reduced to the 10-19 level.

With the support of National Institute of Polar Research (NIPR), absolute gravity measurements were performed in the August 2019 and May 2022 to evaluate the effects of  the 2011 March 11 Tohoku megaquake on coseismic vertical crustal movement. The obtained absolute gravity change between the two periods was -43.8 μGal. This matches the trend of GNSS result obtained by GSI, which show a vertical movement of up to 31.5 mm from August 2019 to May 2022, equivalent to about -10 μGal gravity change, even though the values do not agree precisely.

We have introduced a Micro-g LaCoste's gPhoneX gravimeter for continuous gravity measurements near by the optical clocks in the end of 2021. The preliminary results over seven months detects stable gravity change due to solid-earth tide with about 22 μGal precision. In addition, we have started to investigate the temporal variation of the ground water level at Koganei. We are also monitoring vertical crustal movements by geodetic GNSS measurements. We will investigate uncertainties of optical clocks due to vertical movements caused by geodetic phenomena using continuous gravity and GNSS measurements.

How to cite: Ichikawa, R., Hachisu, H., Sekido, M., Ido, T., Hiraoka, Y., Harima, E., Fukaya, S., Nakashima, M., Matsuo, K., Aoyama, Y., Hattori, A., and Fukuda, Y.: Geodetic measurements and quantitative evaluation for reduced gravitational redshift uncertainty of NICT optical frequency standards, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2983, https://doi.org/10.5194/egusphere-egu23-2983, 2023.

vGGGS.5
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EGU23-11358
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ECS
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Highlight
Yuto Nakamura, Shun-ichi Watanabe, Tadashi Ishikawa, Koya Nagae, and Yusuke Yokota

The GNSS-Acoustic ranging combination technique (GNSS-A) is a method to precisely measure the absolute position of the seafloor benchmark in the centimeter level by combining GNSS and acoustic ranging. The Hydrographic and Oceanographic Department of the Japan Coast Guard (JCG) has been conducting GNSS-A observation at 27 seafloor sites along the Japan Trench and the Nankai Trough named the Seafloor Geodetic Observation Array (SGO-A), to reveal the geophysical processes related to megathrusts that occur at the subduction zones along the Japanese archipelago. From the observations at the SGO-A sites along the Japan Trench, we have discovered the co- and postseismic processes of the 2011 Tohoku-oki Earthquake (Sato et al. 2011; Watanabe et al. 2021). Heterogeneous interplate coupling (Yokota et al. 2016) and shallow slow slip events (Yokota and Ishikawa 2020) have been revealed by observation along the Nankai Trough.

Currently, JCG conducts routine analysis using the open-source GNSS-A analysis software GARPOS (Watanabe et al. 2020). We are aiming an “open” GNSS-A, and the SGO-A coordinate time series obtained from the routine analysis are published online. In this presentation, we review our observation and analysis methods, and discuss on the latest observation results obtained at the SGO-A sites. Additionally, we also introduce our GNSS-A data format, which we have been discussing in the seafloor geodesy data standardization task force of the Inter-Commission Committee on Marine Geodesy (ICCM) in the International Association of Geodesy.

How to cite: Nakamura, Y., Watanabe, S., Ishikawa, T., Nagae, K., and Yokota, Y.: Japan Coast Guard's GNSS-A seafloor geodetic observation: analysis scheme and development of data format, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11358, https://doi.org/10.5194/egusphere-egu23-11358, 2023.

vGGGS.6
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EGU23-11203
Koya Nagae, Tadashi Ishikawa, Shun-ichi Watanabe, Yuto Nakamura, and Yusuke Yokota

Japan Coast Guard (JCG) has been developing seafloor geodetic observation with positioning accuracy at the centimeter level using the Global Navigation Satellite System – Acoustic ranging combination technique (GNSS-A). JCG has deployed a seafloor geodetic observation network called SGO-A along the Japan Trench and the Nankai Trough, where megathrust earthquakes have repeatedly occurred. Up to the present, observations at the SGO-A sites showed the crustal deformation caused by the 2011 Tohoku earthquake (Sato et al., 2011), the subsequent viscoelastic relaxation (Watanabe et al., 2021), the interplate coupling of the Nankai Trough (Yokota et al., 2016) and shallow slow slip events along the Nankai Trough (Yokota & Ishikawa, 2020). Currently, JCG publishes the position time series of the SGO-A sites analyzed by the open-source software GARPOS (Watanabe et al., 2020), based on the empirical Bayesian method.

Recent efforts to improve of the accuracy of GNSS-A seafloor geodetic observation have revealed that there is a wide variety of GNSS-A observation error factors. So far, some error factors have been pointed out, such as the disturbances in the underwater sound speed structure (Yokota et al., 2019) and the influence of the observation plan (Nakamura et al., 2021). In addition, data reanalysis and water tank experiments have clarified that waveform reading errors in acoustic ranging, device characteristics and angle dependence of the acoustic sonar have a great influence on seafloor station positioning analysis. In this presentation, we discuss the error factors in such GNSS-A observations while comparing with the error factors in GNSS observations. For some of the error factors, we introduce our efforts to improve the observation accuracy. 

How to cite: Nagae, K., Ishikawa, T., Watanabe, S., Nakamura, Y., and Yokota, Y.: Various error factors in GNSS-A seafloor geodetic observation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11203, https://doi.org/10.5194/egusphere-egu23-11203, 2023.

vGGGS.7
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EGU23-3731
Using Predicted Ocean Angular Momentum for Earth Orientation
(withdrawn)
Nicholas Stamatakos, David Salstein, Dennis McCarthy, and Mark Psiaki