List of Abstracts



Name : AKSIM Dan

Institut : Institute of Applied Astronomy of the Russian Academy of Sciences

Co-Authors : Dan Aksim, Dmitry Pavlov

Type of presentation : ORAL

Country : RUSSIA

Title : On the Extension of Adams-Bashforth-Moulton for Numerical Integration of Delay Differential Equations and Application to the Moon's Orbit

Abstract : One of the problems arising in modern celestial mechanics is the need of precise numerical integration of dynamical equations of motion of the Moon. The action of tidal forces is modeled with a time delay and the motion of the Moon is therefore described by a functional differential equation (FDE) called delay differential equation (DDE). Numerical integration of the orbit is normally being performed in both directions (forwards and backwards in time) starting from some epoch (moment in time). While the theory of normal forwards-in-time numerical integration of DDEs is developed and well-known, integrating a DDE backwards in time is equivalent to solving a different kind of FDE called advanced differential equation, where the derivative of the function depends on not yet known future states of the function. We examine a modification of Adams-Bashforth-Moulton method allowing to perform integration of the Moon's DDE forwards and backwards in time and the results of such integration.

Name : AKSIM Dan

Institut : Institute of Applied Astronomy of the Russian Academy of Sciences

Co-Authors : Dan Aksim, Alexey Melnikov, Dmitry Pavlov, Sergey Kurdubov

Type of presentation : POSTER

Country : RUSSIA

Title : On the Investigations of the Electron Density in the Solar Corona with Very Long Baseline Interferometry

Abstract : The Sun's corona has interested researchers for multiple reasons, including the search for solution for the famous coronal heating problem and a purely practical consideration of predicting geomagnetic storms on Earth. There exist numerous different theories regarding the solar corona; therefore, it is important to be able to perform comparative analysis and validation of those theories. One way that could help us move towards the answers to those problems is the search for observational methods that could obtain information about the physical properties of the solar corona and provide means for comparing different solar corona models. In this work we present evidence that VLBI observations are, in certain conditions, sensitive to the electron density of the solar corona and are able to distinguish between different electron density models, which makes the technique of VLBI valuable for the solar corona investigations. Recent works on the subject used a symmetric power-law model of the electron density in solar plasma; in this work, an improvement is proposed based on a 3D numerical model.

Name : BIZOUARD Christian

Institut : Observatoire de Paris, IERS

Co-Authors : C. Bizouard, I. Nurul Huda

Type of presentation : POSTER

Country : FRANCE

Title : Polar motion resonance parameter in the diurnal band

Abstract : The polar motion resonance parameters (T,Q) are determined by the Earth rheological properties pertaining both to the mantle and the oceans. For the common polar motion, with periods much larger than 1 day, the quasi-elastic regime of the mantle and the hydrostatic behaviour of the oceans leads to the values T=433+/-4 days and Q=(30,200), that are reflected by the resonating Chandler oscillation. But in the diurnal band, the oceans do not respond anymore hydrostatically, and the mantle deformation is perturbed by the free core nutation. From ocean tidal model, and knowledge of the effect of the free core nutation resonance on k2, we derive expressions of T and Q in the retrograde diurnal band. Nutation VLBI observations partly confirm this model.

Name : BöHM Sigrid

Institut : Department of Geodesy and Geoinformation, TU Wien

Co-Authors : Sigrid Böhm and David Salstein

Type of presentation : POSTER

Country : AUSTRIA

Title : Next generation of coupled climate models and the predicted atmospheric excitation of length of day

Abstract : The Coupled Model Intercomparison Project (CMIP) is an initiative of the World Climate Research Programme with the aim to better understand past and future climate changes due to natural variability or in response to changing radiative forcing. A variety of different groups and Earth system models from all over the world are contributing to the ongoing CMIP phase 6. Such models relate to physical variables of the atmosphere, ocean, and other climate elements. In this presentation we identify models and experimental designs common to the previous CMIP5 and to CMIP6 and show the differences between the project phases. Both CMIP phases use the so-called Representative Concentration Pathways (RCP) to simulate future greenhouse gas concentration trajectories in terms of a possible rate of radiative forcing values in the year 2100, and may be related to socioeconomic factors. Our main focus is on the comparison of axial angular momentum and length of day derived from global wind fields associated with different model runs from historical times to the future centuries.

Name : BROWN Anthony

Institut : Leiden Observatory

Co-Authors : Brown, A.G.A.

Type of presentation : ORAL

Country : NETHERLANDS

Title : Gaia mission

Abstract : Depending on interest and complementarity to the rest of the programme I can give a talk on the Gaia mission in general (status, mission extension, etc), on the scientific impact of Gaia astrometry so far, or on any specific topic that the SOC wishes to see addressed. Also happy to leave the floor to others.

Name : CAPITAINE Nicole

Institut : Observatoire de Paris/SYRTE

Co-Authors : N. Capitaine et al.

Type of presentation : ORAL

Country : FRANCE

Title : The IAU Commission "Earth Rotation" and the IAU 2000 definition of the pole and UT1

Abstract : The IAU 2000/IUGG 2003 resolutions on reference systems include new definitions and concepts concerning Earth's rotation (the pole and UT1) that have been implemented. The aim of this presentation is to report on the role of Commission 19 on Earth rotation for preparing this reform and its implementation in close cooperation with the IERS. This is related to the session of the 100-year history of the IAU Commission 19/A2.

Name : CHARLOT Patrick

Institut : Laboratoire d'Astrophysique de Bordeaux

Co-Authors : P. Charlot, C. Garcia-Miro, T. An, B. Campbell, F. Colomer, A. de Witt, P. Edwards, S. Lambert

Type of presentation : ORAL

Country : FRANCE

Title : Looking into the future of the radio reference frame with SKA

Abstract : The Square Kilometre Array (SKA), to be constructed in the next decade, will be the premier radio astronomical instrument at low and mid radio frequencies (up to 15 GHz) for the next 30 years or so thanks to its large collecting area and versatility. Apart from standalone use, a specific VLBI capability is being developed so that the instrument could be inserted into VLBI arrays, thus creating long baselines with unsurpassed sensitivities. For example, a baseline sensitivity of 0.1 mJy will be reached after a 1 min observation between the phased-up mid-frequency SKA array and a 30 m-class VLBI telescope. Taking advantage of this capability, we are developing a science case to massively densify the radio reference frame. The goal would be to conduct a survey of 50,000 extragalactic sources selected randomly from the Gaia celestial reference frame (i.e. about 10% of the frame) and to measure their astrometric positions with sub-milliarcsecond accuracy. The scientific objectives are: (i) to assess the detection rate of the Gaia sources when observed in radio with high sensitivity, (ii) to densify the current VLBI celestial reference frame, i.e. the ICRF3 which comprises 5000 sources, by an order of magnitude, and (iii) to assess the level of coincidence between optical and radio positions on a statistical basis and infer the geometric properties of the underlying active galactic nuclei. The foreseen VLBI networks that could observe jointly with SKA are the EVN (European VLBI Network), including telescopes in Asia, the developing AVN (African VLBI Network), and the Australian LBA (Long Baseline Array).

Name : CHENG Yu-Ting

Institut : Nanjing University

Co-Authors : Y.-T. Cheng, J.-C. Liu, and Z. Zhu

Type of presentation : POSTER

Country : CHINA

Title : Analyses of celestial pole offsets with VLBI, LLR, and optical observations

Abstract : Aims. This work aims to explore the possibilities of determining the long-period part of the precession-nutation of the Earth with techniques other than very long baseline interferometry (VLBI). Lunar laser ranging (LLR) is chosen for its relatively high accuracy and long period. Results of previous studies could be updated using the latest data with generally higher quality, which would also add ten years to the total time span. Historical optical data are also analyzed for their rather long time-coverage to determine whether it is possible to improve the current Earth precession-nutation model. Methods. Celestial pole offsets (CPO) series were obtained from LLR and optical observations and were analyzed separately by weighted least-square fits of three empirical models, including a quadratic model, a linear term plus an 18.6-year nutation term, and a linear term plus two nutation terms with 18.6-year and 9.3-year periods. Joint analyses of VLBI and LLR data is also presented for further discussion. Results. We improved the determination of the nutation terms with both VLBI and LLR data. The VLBI data present the most reliable feature of the CPO series with the highest accuracy, and they are most important for determining the precession-nutation of the Earth. The standard errors of CPO obtained from the LLR technique have reached a level of several tens of microarcseconds after 2007, but they are probably underestimated because the models used in the calculation procedure are not perfect. Nevertheless, the poor time resolution of LLR CPO series is also a disadvantage. However, this indicates that LLR has the potential to determine celestial pole offsets with comparably high accuracy with VLBI in the future and to serve as an independent check for the VLBI results. The current situation of LLR observations is also analyzed to provide suggestions for future improvement. The typical standard error of CPO series from historic optical observations is about two hundred times larger than that of the VLBI series and can therefore hardly contribute to the contemporary precession-nutation theory. This research is funded by the National Natural Science Foundation of China (NSFC) No. 11473013 and No. 11833004.

Name : CHO Jungho

Institut : Korea Astronomy and Space Science Institute

Co-Authors : Sung-Ho Na, Jungho Cho, Ki-Weon Seo, Kook-Hyoun Youm, Wenbin Shen

Type of presentation : POSTER

Country : SOUTH KOREA

Title : The annual wobble excitation due to the seasonal atmospheric loading on continents

Abstract : Northern Eurasian continent has been regarded as the main source of seasonal atmospheric pressure loading, producing the annual wobble of the Earth polar motion. Prior to the 1980's, when reliable data of global atmospheric pressure were not accessible, this dominance had remained an hypothesis. Nowadays, however, European Centre for Medium-Range Weather Forecasts and National Center for Environmental Prediction produce reliable datasets, that allow to clearly quantify this unique feature. Both Earth’s polar motion and global atmospheric state being known with unprecedented accuracy, we hereby scrutinize to which extent Siberia and Manchuria dominate the annual polar motion.

Name : DAMLJANOVIC Goran

Institut : Astronomical Observatory

Co-Authors : G. Damljanovic, F. Taris, M.D. Jovanovic

Type of presentation : ORAL

Country : SERBIA

Title : Short-term and long-term flux variability of extragalactic objects useful for the future Gaia CRF

Abstract : Some Active Galactic Nuclei objects - AGNs (blazars, for example) are well known for their rapid flux variability across the whole electromagnetic spectrum, and they are variable on diverse time-scales (from minutes through months to even decades). There are three classes of variability: intraday one or IDV (from a few minutes to several hours and flux changes by a few tenths of magnitude), short-term or STV and long-term or LTV (from several days to months and months to decades, respectively). Also, photometry is a powerful tool to investigate AGNs by measuring their variability time-scales, amplitude and duty cycle. We did optical observations (during few years) of AGNs (mostly QSOs) useful for the future Gaia Celestial Reference Frame to study their flux and color variability on short-term and long-term time-scales. The results of some our investigation of mentioned objects were published but for the period of the magnitudes in the range 20-70 days. Here, some STV and LTV are presented.

Name : DE WITT Aletha

Institut : South African Radio Astronomy Observatory

Co-Authors : de Witt, Jacobs, Gordon, Krasna, Le Bail, McCallum, Quick, Soja, Horiuchi

Type of presentation : ORAL

Country : SOUTH AFRICA

Title : The K-band Celestial Reference Frame Roadmap

Abstract : The IAU adopted K-band as a component of the third international Celestial Reference Frame (ICRF-3), in August 2018. Comparison of the K-band and S/X components of the ICRF3 shows spherical harmonic differences at the 30 µas level — the same level as the reported noise floors of each frame. The goal of the K-band team is to push our aggregate noise floor to 20 µas or better. If that is achieved, the advantage of the more compact structure at K-band relative to S/X will come to the fore enabling a truly improved frame. In order to improve the accuracy of the K-band celestial reference frame we are pursuing: (1) improved sensitivity through higher data rates (2 to 4 Gbps), improved antenna efficiency (updated pointing models, panel adjustment, subreflector focussing) and larger apertures (e.g. the addition of the 50m Large Millimetre Telescope); (2) improved ionospheric calibrations through improve temporal and spatial resolution; and (3) improved geometry through the addition of longer north south baselines. We will present an initial timetable for such improvements and an estimate of the impact of each improvement.

Name : DE WITT Aletha

Institut : South African Radio Astronomy Observatory

Co-Authors : de Witt, Jacobs, Nickola, Gordon, Krasna, Le Bail, McCallum, Quick, Soja, Horiuchi

Type of presentation : POSTER

Country : SOUTH AFRICA

Title : The K-band Celestial Reference Frame: First Imaging Results

Abstract : A K-band (24 GHz) celestial reference frame of more than 900 sources covering the full sky has been constructed using over 0.6 million observations from about 70 observing sessions from the VLBA and HartRAO-Hobart. Observations at K-band are motivated by their ability to access more compact source morphology and reduced core shift relative to observations at the historically standard S/X-band (2.3/8.4 GHz). At the standard S/X frequencies, many ICRF radio sources exhibit spatially extended structure that may vary in both time and frequency, degrading the accuracy of estimated source positions. The factor of three increase in interferometer resolution at K-band should resolve out source structure which is a concern for AGN centroid stability. Our more recent VLBA astrometric observations at 2 Gbps provide sensitive, high-resolution multi-epoch imaging of hundreds of sources at K-band. Many of these sources will be imaged for the first time at frequencies above X-band. These K-band images will allow to map the intrinsic source structure so that their astrometric quality can be evaluated at higher frequencies. Recently, we have also successfully demonstrated VLBA dual-polarisation observations using Mark-6 recorders at 4 Gbps. We will improve our imaging science by being early adopters of the Mark-6 dual-polarisation configuration, thereby enabling full polarisation imaging. In this poster we present imaging results from our first VLBA K-band astrometric observations at 2 Gbps. We also present preliminary dual polarisation imaging results from our first 4 Gbps test observations using the VLBA.

Name : DÉBARBAT Suzanne

Institut : Observatoire de Paris

Co-Authors : S. Débarbat

Type of presentation : POSTER

Country : FRANCE

Title : Le système solaire selon Cassini I

Abstract : Après les découvertes de Galilée, dans le Système solaire au début du XVIIe siècle, la seconde moitié du siècle fut fertile en découvertes de nouveaux objets grâce à  l'utilisation des lunettes de grande longueur focale allant jusqu'à  une cinquantaine de nos mètres modernes. Un bilan est établi, fondé sur des documents des Archives de l'Observatoire de Paris, montrant la richesse de ce fonds utilisé, notamment au JPL, pour la navigation spatiale des sondes Voyager I et II dans le Système solaire.

Name : DEHANT Veronique

Institut : Royal Observatory of Belgium

Co-Authors : V. Dehant, A. Houliez, R. Laguerre, J. Rekier, S.A. Triana, A. Trinh, T. Van Hoolst, P. Zhu

Type of presentation : ORAL

Country : BELGIUM

Title : Progress in understanding nutations

Abstract : We shall present an overview of the recent activities within the project RotaNut – Rotation and Nutation of a Wobbly Earth, an ERC Advanced Grant funding from the European Research Council. We have recomputed the Basic Earth Parameters from recent VLBI series and we interpret them in terms of physics of the Earth's deep interior. This includes updates of the nutational constraints on Earth's internal magnetic field and inner core viscosity, as well as of the coupling constants at the core-mantle boundary (CMB) and inner core boundary (ICB). We have explored on simplified Earth models the interactions between rotational and inertial modes. With the help of numerical simulations, we have also addressed the coupling between the global rotation and the inertial waves in the fluid core through parametric instabilities. Special interests have been given to the influence of the inner core onto the stability properties of the liquid core and the large scale formation in the turbulent flow through inverse cascade of energy. The role of precession and nutation forcing for the liquid core is characterized as well as the interaction between the Free Core Nutation (known as the spin-over mode in the fluid core community) and inertial waves.

Name : DELVA Pacôme

Institut : Sorbonne Université - Observatoire de Paris

Co-Authors : P. Delva and N. Puchades

Type of presentation : ORAL

Country : FRANCE

Title : A gravitational redshift test using eccentric Galileo satellites

Abstract : We are going to present the results of the analysis of the GREAT (Galileo gravitational Redshift test with Eccentric sATellites) experiment from SYRTE (Observatoire de Paris), funded by the European Space Agency. The General Relativity (GR) predicts that time flows differently for two clocks that have a relative speed and are placed in different gravitational potentials. It is therefore possible to test GR by comparing the frequencies of two clock, in a so-called gravitational redshift test. The best test to date was performed with the Gravity Probe A (GP-A) experiment in 1976 with an uncertainty of 1.4 × 10^(−4). An elliptic orbit induces a periodic modulation of the fractional frequency difference between a ground clock and the satellite clock, while the good stability of Galileo clocks allows to test this periodic modulation to a high level of accuracy. Galileo 201 and 202, with their large eccentricity and on-board H-maser clocks, are perfect candidates to perform this test. However, the accuracy of the gravitational redshift test is limited by the systematic uncertainty due to orbital errors, and Satellite Laser Ranging (SLR) measurements are crucial to understand them. SLR data allows us to reduce the effect of the systematics, in particular to partly decorrelate the orbit perturbations from the clock errors. By analyzing several years of Galileo satellites data we have been able to improve on the GP-A test of the gravitational redshift.

Name : DILL Robert

Institut : GFZ

Co-Authors : R. Dill, H. Dobslaw

Type of presentation : POSTER

Country : GERMANY

Title : The importance of seasonal sea-level variations from geophysical models and satellite gravimetry for excitation of length-of-day

Abstract : Global mass redistribution between the oceans, the atmosphere, and the continental hydrosphere cause a predominantly seasonal signal in Earth rotation excitation that is not negligible in terms of intra-annual polar motion and especially length-of-day changes. A consistent consideration of the global mass balance among atmosphere, ocean, and continental water is necessary to compare simulated effective angular momentum functions for earth rotation from geophysical models with geodetic observations. In addition to atmospheric, oceanic, and hydrological contributions, we estimate the contributions due to the global mass balance effect using the new ESMGFZ products. At seasonal timescales the global mass balance effect nearly cancels all the contributions to the length-of- day variations simulated by the hydrological model. Comparisons with former studies indicate that the global mass balance effect depends essentially on the choice of the hydrological model and has to be estimated for each combination of geophysical Earth system models individually. Length-of-day changes calculated for barystatic sea-level changes derived from GRACE satellite observations can help to validate the geophysical modes in describing the large-scale mass redistributions on seasonal timescales. Good correlations between observed and modeled global mass balance excitations lead to the conclusion, that the discrepancies between observed length-of-day variations and the Earth rotation excitation from geophysical models is most likely caused by errors of the atmospheric models, in particular of the wind fields.

Name : DORLAND Bryan

Institut : USNO

Co-Authors : Dorland, Secrest, Johnson, Zacharias, Fey, Finch, Fischer, Hunt, Souchay

Type of presentation : ORAL

Country : USA

Title : The Fundamental Reference AGN Monitoring Experiment (FRAMEx) Collaboration

Abstract : The US Naval Observatory USNO) and Paris Observatory (OP) are collaborating on the Fundamental Reference AGN Monitoring Experiment (FRAMEx). FRAMEx is a coordinated effort to use USNO, OP, and other observational assets in multiple spectral bands and located around the world and in orbit to observe and monitor Active Galactic Nuclei in order to better understand their underlying astrophysics and how this affects their suitability as reference objects. We discuss the assets available to support FRAMEx, the key questions, and the specific research thrusts ongoing and planned. We will include information for both the “Volume Limited” and “Deep South” investigations, as well as potential future observations involving deployment of new instruments.

Name : ESCAPA Alberto

Institut : University of León

Co-Authors : A. Escapa, J. Getino, J.M. Ferrándiz, & T. Baenas

Type of presentation : ORAL

Country : SPAIN

Title : Second-order effects in IAU2000 nutation model

Abstract : Second-order effects, in the sense of perturbation theories, of IAU2000 nutation model (Mathews et al. 2002) are inherited from the Hamiltonian rigid Earth nutations REN2000 (Souchay et al. 1999). The transformation to IAU2000 non-rigid Earth model is made by applying the same frequency-dependent transfer function as in the case of first order nutations. We analyze the nature of the second-order effects considered in REN2000 and the used way to derive their corresponding non-rigid contributions. In addition, we discuss the existence of some additional second order terms that, in contrast to the rigid model, might play a role for the non-rigid Earth. The situation is exemplified for a Poincaré non-rigid Earth model, obtaining the second-order nutations of the figure axis by means of a Hamiltonian approach.

Name : ESCAPA Alberto

Institut : University of León

Co-Authors : Alberto ESCAPA

Type of presentation : POSTER

Country : SPAIN

Title : On internationally adopted precession and nutation models

Abstract : On the centennial celebration of IAU Commission A2 “Rotation of the Earth”, we review the models of the precession and nutation of the Earth that have served as standards since Paris Conference of 1896, constructing a time line of their evolution. We describe the main features of the dynamical theories supporting them, as well as IAU resolutions deciding or recommending their implantation. Special attention is paid to the standards in force in the last decades, since they entailed the transition from rigid to non-rigid Earth models.

Name : EUBANKS Marshall

Institut : Space Initiatives Inc

Co-Authors : T.M. Eubanks, L. Petrov

Type of presentation : ORAL

Country : USA

Title : COMPASS: Applications of VLBI Beacons in Cislunar Space

Abstract : The large constellations of spacecraft planned for use in cislunar space (on the Lunar surface, in Lunar orbit, and in the vicinity of the Lunar Gateway) require new solutions for positioning and navigation. COMPASS (Combined Observational Methods for Positional Awareness in the Solar System) is a spacecraft navigation system being developed to provide cost-effective techniques for the positioning of large numbers of spacecraft in cislunar space. COMPASS will use beacons that emit noise at 0.5-1.0 GHz bandwidth at several bands within the 2-14 GHz range and is designed to be interoperable with the routine modes of the new VLBI Global Observing System (VGOS). COMPASS+VGOS should be able to provide rapid determination of interferometric observables (phase delay and plasma dispersion with picosecond level accuracies) during routine VGOS observing sessions. Multi-baseline phase-referenced COMPASS-VGOS observations with simultaneous calibrator observations should thus enable decimeter accuracy transverse positioning with small (credit-card sized) beacons and a few seconds of observations. While COMPASS technology will be applicable to a wide variety of exploration missions and commercial endeavors, a combined COMPASS beacon and Lunar Laser Ranging (LLR) laser retroreflector on the Lunar surface would provide an immediate and strong scientific return, directly tying the Lunar reference frame into the International Celestial Reference Frame (ICRF) and providing independent estimates of Lunar orbit and librations, providing complementary data useful in tests of General Relativity and in determining the internal dynamics of the Moon. Surface beacons would also provide phase reference sources for orbiting beacons in support of time-critical Lunar operations, such as during landing navigation.

Name : FERNáNDEZ Laura Isabel

Institut : Laboratorio MAGGIA. FCAG. Universidad Nacional de La Plata

Co-Authors : L. I. Fernández, S. Böhm

Type of presentation : POSTER

Country : ARGENTINA

Title : Influence of the 2015-2016 ENSO event on length of day variations

Abstract : Since the 90’s it is very well known that the El Niño event involves a large atmospheric excitation that causes inter-annual variations in Earth’s rotation rate. Moreover, the stratospheric event known as the quasi-biennial oscillation (QBO) is usually coupled to El Niño and thus the phenomenon known as ENSO (El Niño-Southern-Oscillation) induces changes of the Earth rotation rate at inter annual scales. According to Newman et al., (2016) an anomalous feature in the QBO during the Northern Hemisphere winter of 2015-2016 is reported for the first time since 1980. The expected downward propagation of the westerly phase of the stratospheric winds was modified and there was an anomalous upward displacement from∼30 hPa to 15 hPa. Afterward, Barton & McCormack (2017) linked this QBO feature with the last ENSO phenomenon 2015-2016, that turned out to be one of the strongest ENSO events registered. Following Lambert et al., (2017) the unusual ENSO 2015-2016 event resulted a mix kind Eastern Pacific -Central Pacific confirming its extreme and unique characteristics. Recently, we investigated the influence of the QBO anomaly detected during the very strong El Niño event 2015-2016 on the observed Earth rotation rate and the associated AAM (Fernandez & Böhm, 2019). Our results indicate that the stratospheric contribution is not powerful enough to justify the LOD anomalies but the tropospheric contribution of the combined ENSO effect does. In this work, we apply the Principal Component Analysis (PCA) in order to study the relative ENSO contribution to the observed LOD variations from different areas. References: Barton, C. A., & McCormack, J. P. (2017). Origin of the 2016 QBO disruption and its relationship to extreme El Niño events. Geophysical Research Letters, 44, 11,150–11,157. doi:10.1002/2017GL075576 Fernández L.I., Böhm S., (2019) Influence of the abnormal QBO feature during 2015-2016 on the Earth rotation rate. (https://meetingorganizer.copernicus.org/EGU2019/EGU2019-5493.pdf) Lambert S.B., Marcus S.L., de Viron O. (2017) Atmospheric torques and Earth’s rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño? Earth Syst. Dynam., 8, 1009–1017, doi: 10.5194/esd-8-1009-2017. Newman, P. A., Coy L., Pawson S., Lait L. R. (2016) The anomalous change in the QBO in 2015–2016, Geophys. Res.Lett., 43, 8791–8797, doi:10.1002/2016GL070373.

Name : FERRáNDIZ José M.

Institut : University of Alicante VLBI Analysis Centre

Co-Authors : J. M. Ferrandiz, R.S. Gross, A. Escapa, J. Getino, A. Brzezinski, R. Heinkelmann

Type of presentation : ORAL

Country : SPAIN

Title : Outcomes of the activities of the IAU/IAG Joint Working Group on Theory of Earth rotation and validation

Abstract : We report on the activities developed by the IAU/IAG Joint Working Group on Theory of Earth rotation and validation in the term 2015-2019 and their main outcomes. The presentation is intended as a summary and update of the previous reports to the International Association of Geodesy (IAG) and the International Astronomical Union (IAU), particularly the triennial report 2015-2018 to the IAU Commission A2, and the final term report to the IAG Commission 3, available in the Travaux 2015-2019. According to them (1) The space geodetic techniques have improved to the point that the theoretical results are judged less accurate than the observational results and therefore the current theory of the Earth’s rotation needs to be improved in several aspects; and (2) The theory suffers from inconsistencies that are not negligible at the level of accuracy set by GGOS, the IAG Global Geodetic Observing System, and at least several components of it require updating or better modeling. Based on the results of the JWG TERV activity, the IAG adopted its 2019 Resolution 5 on the "Improvement of the Earth’s Rotation Theories and Models", which will be addressed also in the presentation.

Name : FIENGA Agnès

Institut : Geoazur, Observatoire de la Côte d'Azur

Co-Authors : A. Fienga, L. Bernus, P. Deram, A. Di Ruscio, O. Minazzoli, J. Laskar, M. Gastineau

Type of presentation : ORAL

Country : FRANCE

Title : the new planetary ephemerides INPOP19a and applications

Abstract : In this talk we will present the new INPOP planetary ephemerides as well as some applications in general relativity, determination of asteroid masses and others.

Name : FODOR Csilla

Institut : Eötvös Loránd University, MTA CSFK Geodetic and Geophysical Institute, GFZ

Co-Authors : Cs. Fodor, R. Heinkelmann, S. Modiri, S. Raut, H. Schuh and P. Varga

Type of presentation : ORAL

Country : GERMANY

Title : Impact of major earthquakes on variations of Earth rotation

Abstract : The study of Earth rotation parameters (ERP) provides valuable information for studying many geophysical phenomena such as the interactions between Earth rotation and earthquake activity. During the last decade, many studies indicate that elastic stress release due to extreme seismic events can potentially cause variations in the Earth rotation. In this study, we aim to search for the signatures of major seismic events in the ERP data derived from space geodetic technique observations, e.g., very long baseline interferometry (VLBI). For this purpose, we use the ERP time-series derived from VLBI measurements and the latest information about earthquakes to explore the effects that strong seismic events have on the rotation of Earth. Our preliminary investigations revealed some promising results that could potentially improve the understanding of the contributions of seismicity to the Earth rotation variation.

Name : FOLGUEIRA Marta

Institut : Faculty of Mathematics, Complutense University of Madrid

Co-Authors : M. Folgueira, J. Souchay

Type of presentation : POSTER

Country : SPAIN

Title : 30 years-evolution in the modelling of the rotation of the rigid Earth: new effects and developments

Abstract : This paper deals with the effects and developments in the advanced mathematical modelling for the rotational motion of the rigid Earth model over the years 1989 to 2019. The analysis focuses firstly on the close link between the improvement of the accuracy and the associated effects. Then, and considering the high precision in the studies involving the interaction between Earth's rotation and geophysical processes, it becomes necessary to extend the developments of the rotation of the rigid Earth in order to reach a suitable precision in both rigid and non-rigid nutation series. Finally, some new additional effects are presented using Hamiltonian formulation of the rotation.

Name : FOLGUEIRA Marta

Institut : Faculty of Mathematics, Complutense University of Madrid

Co-Authors : A.A. Chicharro, V. Puente, M. Folgueira, J. Souchay

Type of presentation : POSTER

Country : SPAIN

Title : Influence on Earth satellites due to the close approach of 99942 Apophis

Abstract : Apophis will pass on the 13th of April 2029 at a minimal distance from the center of the Earth of about 38 000 km, which represents a twelfth of the distance between the Earth and the Moon and is of the order of the altitude in a GEO orbit. This implies that there is some likelihood that Apophis’s passage will disrupt the orbit of a GNSS satellite located in geostationary or IGSO orbit. This paper analyzes the perturbation produced by Apophis on the satellites of the GNSS constellations during its maximum approach to the Earth in 2029. We find that the influence of Apophis is of the same order as that due to Neptune. Simulations are performed at different epochs with the aim of determining those configurations of satellites that are most affected by Apophis influence.

Name : FOLGUEIRA Marta

Institut : Faculty of Mathematics, Complutense University of Madrid

Co-Authors : S. Domenech, M. Folgueira

Type of presentation : POSTER

Country : SPAIN

Title : Rotation of Mars and Venus: influence of the zonal harmonic J3

Abstract : This paper deals with the developments for the solar contribution of the potential energy due to the zonal harmonic J3 and its influence on the rotation of Mars and Venus both considered as rigid bodies. At a level of 0.1 µas and for the case of Mars, we have obtained 10 terms for the nutation in longitude and 9 terms for the nutation in obliquity with the major contribution in longitude is equal to: 46 µas cos LS and in obliquity is -53 µas sin LS, both of period annual. In the case of the planet Venus, the major contribution due to the harmonic J3 is larger than for Mars: 2529 µas cos LS for the nutation in longitude y 117 µas sin LS for the nutation in obliquity. The comparison with the Earth is presented at the end of the paper.

Name : GOMEZ Maria Eugenia

Institut : Laboratoire d'Astrophysique de Bordeaux

Co-Authors : M. E. Gomez, P. Charlot, R. Campbell, M. Kettenis, A. Keimpema

Type of presentation : POSTER

Country : FRANCE

Title : Geodesy at K band with the European VLBI Network

Abstract : A non-standard VLBI geodetic experiment was carried out at K band (22 GHz) in June 2018 using 14 radio telescopes from the European VLBI Network (EVN). The purpose of this experiment is to determine accurate geodetic positions for those EVN telescopes that do not possess S/X receivers and hence do not participate in regular experiments organized by the International VLBI Service for geodesy and astrometry (IVS). Even though the EVN is not a geodetic array, there are many reasons why such accurate radio telescope positions are desirable, including frequent observations using the phase-referencing technique to detect weak radio sources. The experiment was fully correlated with the EVN software correlator at JIVE (SFXC) and exported into Mk4 format so that it can be further processed with standard geodesy software packages. Several changes were made at the EVN software correlator and detailed testing was carried out so that the correlator can successfully correlate geodetic experiments. The paper will present the current status of the work, and how we foresee moving towards our objective of delivering accurate geodetic coordinates for the non-geodetic EVN telescopes. Additionally, the experiment will be used to demonstrate the full geodetic capabilities of the EVN software correlator at JIVE. This work is carried out as part of the JUMPING JIVE project funded by the Horizon 2020 Framework Programme of the EU.

Name : GROSS Richard

Institut : Jet Propulsion Laboratory

Co-Authors : R. Gross, A. Brzezinski

Type of presentation : ORAL

Country : USA

Title : The International Astronomical Union and Polar Motion

Abstract : Along with the IAG and IUGG, the IAU has been instrumental in furthering our understanding of polar motion by establishing Services, Projects, and Working Groups to coordinate the acquisition, reduction, analysis, and interpretation of polar motion observations; by organizing Symposia and Colloquia for scientific discourse about polar motion; and by adopting resolutions related to polar motion. The International Latitude Service (ILS) was established by the IAG in 1895 for the purpose of observing the latitude variations caused by the Earth's polar motion. Both the IUGG, which included the IAG as one of its member associations, and the IAU were created in 1919 and at that time they both created commissions on latitude variations. At their first General Assemblies in 1922, the IUGG and IAU created a joint commission on latitude variations and put it in charge of the work of the ILS. The ILS observed latitude variations using visual zenith telescopes at six stations located at 39º08' North latitude and well-distributed in longitude. However, over time many more stations located at different latitudes and using other instruments began observing latitude variations and the accuracy of the resulting polar motion estimates greatly improved. Since polar motion is needed to reduce UT0 observations to UT1, and in order to shorten the delay of publication of UT1, the IAU recommended in 1955 that the ILS begin a Rapid Service for polar motion. This became the Service International Rapide des Latitudes (SIR) of the Bureau International de l'Heure (BIH). Recognizing the contribution of the numerous observatories not located at 39º08' North latitude, in 1962 the IAU and IUGG replaced the ILS with the International Polar Motion Service (IPMS). There were now two international organizations (BIH and IPMS) producing polar motion estimates from essentially the same set of latitude observations. The 1970s saw the development of the space-geodetic techniques of lunar and satellite laser ranging (LLR and SLR) and very long baseline interferometry (VLBI). These techniques could measure polar motion more accurately and with less systematic error than could optical astrometry. With the support of the IUGG, in 1978 the IAU established an international project to Monitor Earth Rotation and Intercompare the Techniques (Project MERIT). The objective of Project MERIT was to foster the development of new techniques for measuring the Earth's rotation and to make recommendations on future international services. To facilitate the intercomparison of results, Project MERIT recognized the value of common data reduction and analysis standards, of co-locating techniques, and of intensive observing campaigns. During its Third Workshop in 1985, Project MERIT recommended that an International Earth Rotation Service (IERS) be established. This was endorsed by the IAU at its General Assembly later in 1985 and by the IAG and IUGG in 1987. The IERS subsequently began operating on 1 January 1988, replacing the IPMS and the Earth rotation section of the BIH.

Name : HEINKELMANN Robert

Institut : GFZ Potsdam

Co-Authors : S. Modiri, R: Heinkelmann (presenting), S. Belda, M. Hoseini, Z. Malkin, J.-M. Ferrandiz, H. Schuh

Type of presentation : ORAL

Country : GERMANY

Title : On the correlation of Celestial Pole Offsets and geomagnetic field variations (recent achievements)

Abstract : The understanding of forced temporal variations of celestial pole offset (CPO) could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG), i.e., 1 mm accuracy and 0.1 mm/year stability on global scales in terms of the ITRF defining parameters. Besides astronomical forcing, CPO excitation depends on the processes in the fluid core and the core-mantle boundary. The same processes are responsible for the variations of the geomagnetic field (GMF). During the last decade, several investigations were conducted to find a possible interconnection of GMF changes with the length of day (lod) variations. However, less attention was paid to the interdependence of the GMF changes to the CPO variations. In this study, we use the CPO time series obtained from very long baseline interferometry (VLBI) observations and the latest GMF data such as geomagnetic jerk, magnetic dipole moment from a state-of-the-art geomagnetic field model to explore the correlation between CPO and GMF. Our preliminary results reveal interesting common features in the CPO and GMF variations, which show the potential to improve the understanding of the GMF's contribution to the Earth rotation. Special attention is given to potential time lags between geomagnetic jerks and rotational variations.

Name : HILTON James

Institut : US Naval Observatory

Co-Authors : J.L. Hilton, S.G. Stewart

Type of presentation : POSTER

Country : USA

Title : Implementation of Improved Magnitude Parameters for Solar System Planetary Ephemerides

Abstract : The joint publications of the U.S. Naval Observatory and Her Majesty’s Nautical Almanac Office contain the most currently recommended fundamental standards into their tables of astronomical data and ephemerides and are often the first publications to implement newly improved constants or methods. To this end, we have integrated the Mallama & Hilton (2018, Astron. & Comp., 25, 10) algorithms to produce improved planetary magnitude and surface brightness values in the physical ephemeris data for Solar System planets. This is a significant step forward in this area of research as prior to this time, calculations were based on equations from the early 1960’s, with only more recent improvements for Mercury and Venus (Hilton 2005). Ephemeris predictions of the illumination of disk of the planets and other Solar System bodies is a non-trivial problem. They are required for factors such as identification, exposure estimates, and offset between center-of-light and center-of-object. These improved magnitude ephemerides will first appear in The Astronomical Almanac for 2021 and The Astronomical Phenomena for 2022. The uncertainty in the V magnitude predictions ranges from 0.04 mag for the outer planets to nearly 0.2 mag for Mars. There is much room for improvement and some of the work underway to further enhance these magnitude ephemerides are discussed. Continual updates to these publications allow them to serve as a worldwide resource and standard for positional astronomy and navigation. In addition, renewed interest into planetary magnitude theory has implications for better predictions of the characteristics of exosolar systems and space navigation.

Name : HOBBS David

Institut : Lund Observatory

Type of presentation : POSTER

Country : SWEDEN

Title : Future Space Astrometry

Abstract : With Gaia's second data release in April of 2018 Europe entered a new era of space astrometry. Further data releases are also planned for the coming years. Despite this great progress astronomers are already looking towards the future. Gaia had an advantage over pointed missions in being a global survey which provided absolute parallaxes and addressed a very broad range of science cases. However, Gaia only operates at optical wavelengths while much of the Galactic centre and the spiral arm regions are obscured by interstellar extinction. One clear option for space astrometry is to shift to the infra-red where new science cases immediately become apparent. This can, of course, be achieved with a pointed mission performing relative astrometry, such as the Japanese small-Jasmine concept, focused on the Galactic plane. However, I would argue that much more can be achieved by essentially replicating a Gaia-like mission with Near-Infra-Red (NIR) detectors.

A NIR mission requires new types of detectors to scan the entire sky and measure global absolute parallaxes. The spacecraft must have a constant rotation resulting in a moving image that must be compensated for by, for example, operating the detectors in Time Delayed Integration (TDI) mode. A new NIR Gaia-like mission separated by a 20 year interval from Gaia would allow: 1) NIR astrometry and photometry to penetrate the obscured regions and to observe intrinsically red objects; 2) improved proper motions with 14-20 times smaller errors than Gaia, which would open up new science cases; 3) the slowly degrading accuracy of the Gaia optical reference frame, which will be the basis for future astronomical measurements, to be maintained and extended to the NIR. However, developing TDI-capable NIR detectors is a difficult and expensive challenge which makes this concept a hard sell. An obvious solution is to collaborate with the US, which also has world leading NIR detector companies. We recently submitted a white papers to the US decadal survey and ESA’s Voyage 2050 call outlining such a collaboration for GaiaNIR.

Name : HøG Erik

Institut : Copenhagen University, Niels Bohr Institute

Co-Authors : E. Høg, D. Hobbs

Type of presentation : POSTER

Country : DENMARK

Title : Gaia Successor with International Participation

Abstract : Astrometric data from the current Gaia are already revolutionizing astronomy in all branches from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In April 2018, the second data release based on 22 months of observations gave 5-parameter astrometry for more than 1.3 billion sources while subsequent releases will give increasingly accurate and comprehensive sets of astrophysical data. The final Gaia data set will presumably be based on 8-10 years of observations thus providing a new astrometric foundation of all astronomy. It is however clear that a Gaia successor in twenty years for observation of the same stars is required in order to maintain and strengthen the astrometric foundation of astronomy. The two missions together will provide motions with 10-20 times better accuracy than Gaia alone for the observed objects, be it stars in the Halo or in galaxies or objects in our solar system or binary stars with sub-stellar components etc. Gaia is an ESA-only mission as Hipparcos was and we thought a Gaia successor should be the same. Recently however, we have realized the importance of strengthening our efforts by international collaboration. This has begun by involving the USA and it appears there is considerable interest also in Japan and Australia. Gaia operates in optical wavelengths, and thus it is blind to several physical processes taking place within obscured regions of the Milky Way. A mission in NIR (at a bandpass of 400-1800 nm), however, would be able to unravel these processes, and would also multiply the number of observed objects giving up to 8 billion newly measured objects. In 2017 ESA studied such a NIR space observatory (GaiaNIR). The outcome was that it requires new types of NIR Time Delay Integration (TDI) detectors to scan the entire sky and to measure global absolute parallaxes. The ESA study also hinted that a US-European collaboration would be the optimal answer to make GaiaNIR science and technology a reality. We have therefore in March 2019 together with US, Japanese and Australian colleagues submitted a proposal available at https://arxiv.org/abs/1904.08836 for such a study in the US Decadal Survey. In July a white paper was submitted to US on development of Scanning NIR Detectors for Astronomy available at https://arxiv.org/abs/1907.05191. Our proposal to ESA at arXiv:1907.12535 was submitted on 26 July 2019.

Name : IVANTSOV Anatoliy

Institut : Akdeniz University

Co-Authors : A. Ivantsov

Type of presentation : ORAL

Country : TURKEY

Title : Astronomical refraction in the Earth’s ellipsoidal atmosphere

Abstract : Uncertainty in astronomical refraction calculation is a permanent contributor to the astrometric error budget of ground-based measurements revealing itself as the zenith distance bias that is considered to be the function of wavelength, zenith distance, and the air refractive index. The most advanced calculations of astronomical refraction for the visible and near-infrared are still done using the spherically symmetric model for the Earth’s atmosphere. We show that the astronomical refraction problem can be formulated as a Cauchy problem for the differential equation of light rays which specifies ray tracing directly in terms of the refractive index function. We provide a comparison of the astronomical refraction calculations in the ellipsoidal model on top of the surface (WGS84) and spherically symmetric model for the Earth’s atmosphere. The air refractive index was calculated using stratification of air in hydrostatic equilibrium following the Standard Atmosphere Parameters GOST4401-81. The ellipsoidal model of atmosphere provides an advanced level of accuracy in calculation of astronomical refraction resulting in both zenith distance and azimuth biases that can be considered in highly accurate ground-based astrometric measurements.

Name : JACOBS Christopher

Institut : JPL

Type of presentation : ORAL

Country : USA

Title : Advancing the X/Ka-band Celestial Frame: Roadmap to the Future

Abstract : The 3rd International Celestial Reference Frame as of 2019 Jan 01 is multi-frequency consisting of components at S/X (2.3/8.4 GHZ), K (24 GHz) and X/Ka (8.4/32 GHz). Observations at X/Ka-band are motivated by their ability to access more compact source morphology and reduced core shift relative to observations at the historically standard S/X-band. In addition, the factor of four increase in interferometer resolution at Ka-band should resolve out some types of astrophysical systematics. The X/Ka celestial reference frame was constructed using a combined NASA and ESA Deep Space Network from about 180 observing sessions over which 678 sources were detected. Currently the XKa frame is limited by spatially correlated systematic errors vs. declination. We will discuss a four point plan to address theses errors: (1) Improve the sensitivity of the baselines from NASA stations to ESA’s Argentina station (2) Improve data weighting using correlated noise (3) Add baselines from JAXA’s 54-meter Misasa, Japan station (4) Develop a prototype broadband 8-35 GHz receiving system for the VLBA

Name : JOHNSON Megan

Institut : USNO

Co-Authors : M. Johnson, N. Secrest, B. Dorland, A. Fey, L. Fernandez, L. Hunt, T. Fischer

Type of presentation : POSTER

Country : USA

Title : A Volume-limited AGN Survey for the FRAMEx Project

Abstract : We present VLBA C-band, 6 cm images of a volume-limited sample of 25 AGNs that have been selected as part of the Fundamental Reference AGN Monitoring Experiment (FRAMEx). FRAMEx is a collaborative project between USNO and Paris Observatory aimed at understanding the fundamental physics of the processes that allow the quasar sources to shine bright in the radio such that they make excellent target sources for the ICRF. The sample presented here are composed of 25 AGNs that have measured distances out to 40 Mpc, are visible to the VLBA and have been selected from the Swift/BAT AGN catalog in a volume-limited manner down to an X-ray luminosity of 10^42 erg/s. Based on the Fundamental Plane of black hole activity (e.g., Merloni et al. 2003), a 10^6 Msun black hole accreting at 10^42 erg/s should have a 5 GHz (C-band), radio luminosity of about 10^36 erg/s. It is this radio sensitivity depth to which all our observations probe such that we can uniformly and systematically determine the parsec-scale radio emission that may be present in each of these objects.

Name : KANG Ki Chun

Institut : Central Information Agency of Science and Technology

Co-Authors : Kang Ki Chun, Kim Kwan U, Sim Jin

Type of presentation : POSTER

Country : DEMOCRATIC PEOPLE'S REPUBLIC OF KOREA

Title : Imaginary Force for Einstein's Theory of Gravitation and the Cause for the Advance of Perihelion in the Planetary Orbits

Abstract : Previous researchers have included gravitational effect 1/r^3 obtained by Einstein as well as Newton law of universal gravitation in Riemannian geometry which treats space-time curvature, and made physics geometric. So they have not made an exact physical analysis of gravitational effect different from Newton universal gravitation potential 1/r, especially have not taken the problem of whether the proper time was the value of the real time dilation indicated by the standard clock existing in noninertial system or not. The paper shows that the gravitational effect obtained by Einstein is the imaginary force introduced in General Relativity through the space component of the four-dimensional force derived when solving the equation of geodesic line in Schwarzshild gravitational field, while analyzing the principal factors that cause the advance of perihelion in the planetary orbits and the value of the real time dilation of the standard clock.

Name : KARBON Maria

Institut : SYRTE, Observatoire de Paris

Co-Authors : C. Gattano, M. Karbon

Type of presentation : POSTER

Country : FRANCE

Title : Parametrization of the source coordinates and its astrophysical interpretation

Abstract : In the ICRF3 catalog, representing the newest realization of the Celestial Reference Frame (CRF) since summer 2018, the positions of the radio sources are given as time invariant coordinate pairs, without distinction. Nevertheless, where systematics within source positions were known for a restricted set of sources (which let to their alienation in the past), new evidence was found for a generalization of such systematics to all reference sources, albeit at different levels and time scales. By neglecting these systematics in the realization of the CRF, its quality may be deteriorated and thus all derived variables, e.g. of the Earth orientation parameters (EOP), as well. A proven approach to overcome these shortcomings is to extend the parametrization of source positions using the multivariate adaptive regression splines (MARS), as they allow automation by combining recursive partitioning and spline fitting in an optimal way. In this study, we investigate source coordinate time series and their residuals resulting after the application said parameterization. We aim to identify the noise level and content of the different time series through the computation of the Allan standard deviation functions. A prospective is to link the corrected noise patterns to specific astrophysical phenomena.

Name : KARBON Maria

Institut : SYRTE, Observatoire de Paris

Co-Authors : M. Karbon

Type of presentation : POSTER

Country : FRANCE

Title : Impact of the parameterisation of the source positions on the Free Core Nutation

Abstract : Within this work investigate the effect of the parameterisation of the source positions used in geodetic VLBI analysis on the estimation of the Free Core Nutation (FCN) parameters. The mitigation of the source position variation has shown to be highly beneficial to the Earth orientation parameter (EOP), especially to the celestial pole offsets (CPO). Hence, we go a step further and explore the impact of the improved source positions on the FCN parameters. Methods. We chose the adaptive algorithm multidimensional regression splines (MARS) to model the time-variation of the source coordinates. Not only does it enable us to correct the ICRF3 a-priori coordinate before entering it into our analysis, but also to choose our datum definition freely as we are no longer limited to stable sources. To determine the best set-up, we tested several configurations. In the next step we estimate the FCN periods and amplitudes for each configuration following two strategies, 1) by deriving them from the CPO and 2) by making use of the resonance effect in the solid Earth tides. In the last step we determine an empirical FCN model based on the estimated periods and the respective CPO time-series.

Name : KIM Kwan U

Institut : Central Information Agency of Science and Technology

Co-Authors : Kim Kwan U, Sim Jin and Choi Se Yong

Type of presentation : ORAL

Country : DEMOCRATIC PEOPLE'S REPUBLIC OF KOREA

Title : On the Basic Factor That Causes the Instabilities of the Earth's Rotation

Abstract : Earth's rotation is one of the astronomical phenomena without which we cannot think of human life. That is why the investigation on the Earth's rotation is very important and has a long history. Invention of quartz clocks in the 1930s and atomic time in the 1950s, and introduction of space geodetic technics into astronomical observation since the 1970's resulted in striking and rapid development of the Earth's rotation study. The theory of the Earth's rotation, however, has not been up to the high level of astronomic observation. We endeavor to quantify the Earth instabilities affecting polar motion, precession-nutation of the Earth's rotation axis, and angular velocity through a single equation derived from Newtonian mechanics. In particular, we prove that the basic factor causing the instabilities of the Earth's rotation are not the variations of the angular momentum changes of the fluid layers but the moment of external force. So this study opens a new direction of research.

Name : LAMBERT Sébastien

Institut : SYRTE, Observatoire de Paris, PSL

Co-Authors : S. Lambert

Type of presentation : ORAL

Country : FRANCE

Title : Atmospheric excitation and torques over the 20th century: how was driven the Chandler wobble?

Abstract : We use the ERA 20C reanalysis gridded surface pressure, friction drag, and wind speed provided by the European Center for Medium-range Weather Forecast (ECMWF) to infer the atmospheric excitation and the associated mountain and friction torques since 1900. Focusing to the Chandler frequency band, we examine the regional contributions, their interannual-to-decadal variability, and their possible link with the main climate oscillations.

Name : LINDEGREN Lennart

Institut : Lund Observatory

Co-Authors : L. Lindegren

Type of presentation : ORAL

Country : SWEDEN

Title : The bright reference frame of Gaia and VLBI observations of radio stars

Abstract : In the Gaia catalogue the positions and proper motions of stars are directly linked to the extragalactic reference frame and ICRF through Gaia's observation of quasars. These are mostly fainter than 18th magnitude, but the global astrometric reduction of Gaia data should ensure that all sources are on the same reference frame. However, comparison with Hipparcos data suggests that this is not quite the case in Gaia DR2: the reference frame of bright (G < 13) stars seems to have a systematic spin of about 0.14 mas/yr relative to the quasar frame. The cause of this systematic in Gaia DR2 is understood and the calibration model is being revised to prevent this kind of error in future Gaia data releases. The issue nevertheless raises an important question, namely how to validate the bright reference frame of Gaia. At the faint end there are enough quasars to provide a very good check, but comparison data of adequate accuracy are very scarce at bright magnitudes. In this contribution I describe a new method to estimate the orientation and spin of the bright reference frame of Gaia using VLBI observations of radio stars. The optimum combination with Gaia data means that even single-epoch VLBI measurements can be extremely useful, especially when taken far from the Gaia epoch. Applied to DR2, using published VLBI data, the method confirms the previously suspected spin of the bright reference frame. With existing data the accuracy is severely limited by the small number of radio stars and their often complicated structure and binary nature. For future Gaia data releases, high-precision VLBI astrometry will be immensely valuable for checking the consistency of Gaia data across all magnitudes, but this will require a sustained effort to obtain VLBI measurements of many more optically bright sources, preferably targeting main-sequence, single stars.

Name : LIU Jia-Cheng

Institut : Nanjing University

Co-Authors : J.-C. Liu, N. Capitaine

Type of presentation : ORAL

Country : CHINA

Title : A possible improvement of the IAU 2006 precession model

Abstract : In this talk, we present our effort to improve the IAU 2006 precession model after more than 10 years of its publication in 2003. Latest analytical and numerical ephemerides of our solar system are used to calculate the long term variation of the EMB orbit around the Sun, i.e. the precession of the ecliptic. To integrate the precession of the equator that is dynamically consistent we applied latest progress on the Earth's rotation theories and an J_2 acceleration model from SLR observations. Our precession expressions have significant difference in the t^3 term of psi_A with respect to the IAU 2006 model. Finally the updated precession expressions were checked by the VLBI CPO time series in the interval of 1979 and 2017. We will also discuss different options of the P03 and P04 solutions when considering the effect of the frame bias, as well as the role of the ecliptic in the future Earth's rotation study. This work was published as Liu J.-C. & Capitane N. 2017, A&A, 597, A83

Name : LIU Niu

Institut : Nanjing Univsersity

Co-Authors : N. Liu, Z. Zhu, S. B. Lambert and J.-C. Liu

Type of presentation : ORAL

Country : CHINA

Title : Is it possible to bring the Gaia-CRF2 into the VLBI data reduction?

Abstract : The very long baseline interferometry (VLBI) is a powerful and unique technique that can determine simultaneously the celestial reference frame (CRF), Earth orientation parameters (EOPs), and the terrestrial reference frame (TRF). The realizations of the CRF and TRF are principally independent of each other and the EOPs connect these two frames. In the VLBI data reduction, several no-net-rotation (NNR) and no-net-translation (NNT) constraints are applied in order to constrain the frames and remove the degeneracies. To address how well the CRF, EOPs, and TRF products are separated, we can usually compare these products with those from other techniques, such as GNSS and LSR. Here we explore a more direct way: is it possible to directly consider another CRF, independent of VLBI and having a comparable accuracy, in the VLBI data processing? The Gaia mission offers a possible option. The Gaia and VLBI measure the position of the same extra-galactic object at different wavelengths. The positional differences of the Gaia and VLBI are supposed to caused by systematic and random errors in either technique and the so-called core-shift effect, only if these two systems are well aligned. This allows us to bring the Gaia-CRF into the VLBI data reduction. We replace the ICRF3 with the Gaia-CRF2 to run global VLBI solutions. Different subsets of quasars and NNR constraints are tested. Then we check the deduced solution with the standard VLBI solution. Preliminary results show a strong dependency of differences between those two solutions on the NNR constraints.

Name : LUNZ Susanne

Institut : GFZ Potsdam

Co-Authors : S. Lunz, R. Heinkelmann, J. Anderson, M. Johnson, A. Fey, O. Titov

Type of presentation : POSTER

Country : GERMANY

Title : Gaia-VLBI: phase-referencing continuum emission observations of optically bright stars with the VLBA (planned proposal)

Abstract : As seen in Gaia Data Release 2, Gaia observations are magnitude dependent due to instrumental reasons. Amongst other things, this shows up in the form of significant spin of the bright (<13 mag) reference frame compared to the faint one. For independent verification of the global orientation and spin, as well as the parallax zero point of optically bright objects obtained from the Gaia mission, positional VLBI observations of radio stars are identified as being the most precise technique by the Gaia collaboration for the upcoming data releases (Lindegren, submitted to A&A). The observations allow an independent test of the calibration of the Gaia instrument for the bright magnitude range, and thus verification for data that is used for many applications, such as positioning and orientation on Earth and in space. Unfortunately VLBI data of radio stars is sparse till today and more observations would be very beneficial. Here, we propose an initial series of three radio star surveys in the continuum emission phase-referencing mode with the VLBA for the (re-)detection of carefully selected candidate stars with promising characteristics for the VLBI-Gaia link. In the first proposal we revisit optically bright stars that have been detected by continuum VLBI observations by various networks in the past. Whereas in the second proposal, we plan to find radio emission of suitable nearby single stars that have never been observed at radio wavelengths before. The third proposal will be for observations of radio stars with detected radio emission in the past, but which are not considered in the first proposal. The latter proposals are for finding new radio stars to optimize the geometrical sky distribution. For those objects successfully detected in one of these surveys, we will apply for another round of observing time to get precise positions, parallaxes, proper motions and non-linear variations, such as those caused by orbital motions in binary systems. For those objects that have been observed in the past by the VLBA, it is possible to include the archived data in the data processing due to the advantageous data policy of the VLBA.

Name : MALKIN Zinovy

Institut : Pulkovo Observatory

Co-Authors : Z. Malkin, A. Brzezinski, N. Capitaine, V. Dehant, R. Gross, C. Huang, D. McCarthy

Type of presentation : ORAL

Country : RUSSIA

Title : Overview of the 100-year history of the IAU Commission 19/A2

Abstract : We provide an overview of the 100-year history of IAU Commission 19/A2 "Rotation of the Earth". It began in 1919 as one of the 32 standing committees formed with the establishment of the IAU. In 1922, the Standing Committee became Commission 19 "Variation of Latitude" as the main topic of the Commission discussions was investigating polar motion, primarily using the results of the International Latitude Service (ILS). In 1964, the Commission was renamed "Rotation of the Earth", reflecting the expansion of its activities to include other available observations and the theory of the Earth's rotation and connections between the Earth's rotation and geophysical phenomena. In the framework of the 2015 IAU re-organization, Commission 19 was renewed as Commission A2 with the same name "Rotation of the Earth". During its whole history, the Commission has been an active part of the IAU, initiating or supporting tens of Union resolutions and recommendations related to the organization and interpretation of the observations of the Earth's orientation, theory of precession-nutation, celestial and terrestrial reference systems and frames, time scales, and other topics of scientific and practical interest. The Commission took part in organization of tens IAU sponsored or co-sponsored meetings. It continues to play an important role in the IAU coordinating international cooperative efforts and providing a link between the astronomical and geodetic communities and a link between the IAU and other organizations such as the International Union of Geodesy and Geophysics (IUGG) and the International Association of Geodesy (IAG). Jointly with the IUGG and IAG, the Commission has organized the International Earth Rotation and Reference Systems Service (IERS) and the International VLBI Service for Geodesy and Astrometry (IVS), and supported organization of the International GNSS Service (IGS), the International Laser Ranging Service (ILRS), and the International DORIS Service (IDS). It also initiated or co-organized many IAU and inter-union working groups on specific topics related to the Commission activities. In 2003, the IAU-IUGG Working Group on "Non-Rigid Earth Nutation Theory" was awarded with the Descartes Prize of the European Union, therewith providing visibility of the work of the Commission 19. Now the Commission continues its long and glorious history by working to improve the organization and accuracy of the Earth's orientation observations, to develop better understanding the Earth's rotation variations, and to improve the accuracy and consistency of celestial and terrestrial reference systems and frames.

Name : MALKIN Zinovy

Institut : Pulkovo Observatory

Co-Authors : Z. Malkin, E. Prudnikova, T. Soboleva, N. Miller

Type of presentation : POSTER

Country : RUSSIA

Title : Outstanding Pulkovo latitude observers Lidia Kostina and Natalia Persiyaninova

Abstract : This contribution is devoted to the memory of Pulkovo astrometrists Lidia Kostina and Natalia Persiyaninova. Lidia Dmitrievna Kostina (December 8, 1926 - June 4, 2010) and Natalia Romanovna Persiyaninova (August 26, 1929 - January 16, 2003) left a bright mark in the history of the Pulkovo Observatory, as well as in the history of the domestic and international latitude services. In the first place, they were absolute leaders in the latitude observations with the famous zenith-telescope ZTF-135. In 1954-2001, they obtained together more than 66’000 highly accurate latitudes, which make about 2/3 of all the observations made by 23 observers with the ZTF-135 after the WW2. They also provided a large contribution to investigation of the instrumental errors, methods of the data analysis, developing of the observing programs. Their results in studies of the latitude variations and polar motion were also highly recognized by the community.

Name : MALKIN Zinovy

Institut : Pulkovo Observatory

Co-Authors : Z. Malkin

Type of presentation : POSTER

Country : RUSSIA

Title : A new equal-area grid on the sphere

Abstract : A new method is proposed to divide a spherical surface into equal-area cells. The method is based on dividing a sphere into several latitudinal bands of near-constant span with further division of each band into equal-area cells. It is simple in construction and provides more uniform latitude step between latitudinal bands than other methods of isolatitudinal equal-area tessellation of a spherical surface.

Name : MAMMADALIYEV Nijat

Institut : TU Berlin

Co-Authors : P.A.Schreiner, S.Glaser, K.Balidakis, K.H.Neumayer, J.M.Anderson, R.Heinkelmann, R Koenig, H.Schuh

Type of presentation : ORAL

Country : GERMANY

Title : On a possible contribution of VLBI to geocenter realization via satellites assessed by simulation study

Abstract : The requirements of 1 mm accuracy and 1mm/decade stability, stated by the Global Geodetic Observing System (GGOS) for studies pertinent to global climate change and their interpretation, require the accurate determination of Earth system center of mass (CoM) variations . Observing extra-galactic radio sources and artificial near-Earth spacecraft orbiting around the instantaneous CoM with VLBI allows the determination of the instantaneous geocenter. In this study, the capability of state-of-the-art VLBI to observe satellites to estimate the geocenter is explored within the project GGOS-SIM-2. Accordingly, space geodetic observations are simulated for different station networks and satellite orbits introducing different error sources with and without various non-tidal geophysical loading models. Moreover, we assess the potential of the current and future VLBI system to estimate the geocenter.

Name : MARCO Francisco J.

Institut : Universitat Jaume I

Co-Authors : Marco, F.J. ; Martí­nez, M-J. ; López, J.A.

Type of presentation : POSTER

Country : SPAIN

Title : AN EXAMPLE TO ANALIZE DISCRETE VECTOR FIELDS ON THE SPHERE USING QUANTITATIVE AND QUALITATIVE METHODS

Abstract : An interesting but sometimes difficult task is the improvement of a ground based catalog using a large number of stars, through a of correction that providing a large period of accuracy. A re-reduction method, based on the extremely accurate data provided by DR2 is not always viable, so we must be satisfied with other possibilities that, as a compensation, intrinsically entail properties missed in the different Gaia versions. There are two advantages that "a priori" seem sufficient to justify further improving ground-based catalogs. The first advantage comes from comparing different ground-based catalogs (either globally or by zones, either in their mean observation times or by establishing different mean observation times according to the data for each star). It is convenient to keep in mind that each catalogue is centered at an epoch and the reduced positions includes errors of observation. The assumption that after the application of a reduction, with a very limited series of observations per star, a mean position can be deduced and the assessment that the mean error attributed is random are not necessary true (nor should it be, using so few data, assigning normal behavior as the statistical model). The decomposition of an error in a systematic part and a random part depends on the adjustment model and its precision. And it is problematic to assume that such a component is random if the statement "for such adjustment model and such precision order" is not added. To summarize this point, the improvement of two ground-based catalogs and their subsequent comparison may explain common parts of the residuals of the adjusted catalog, and then look for a physical explanation: For example as function of certain parameters of terrestrial rotation in certain mean observation times. The second advantage can, if achieved, reinforce the former. The question is: to what extent can we improve the positions of a ground-based catalog, so that its accuracy is (in the whole sphere, in an spherical area or on a certain set of stars) as comparable as possible to those of (modestly, of course) DR1 or DR2?. Since we must have aligned the system defined by Gaia with ICRF, why not try to repeat this for positions observed from Earth? Can this be arranged while conserving the intrinsic property that comes from observation from Earth? That being said, it is an impossible task, but we can lower the expectations in the following way: a) studying quantitative improvements that eliminate biases; b) and determining qualitative properties of the residual vector field related to their singular points. The techniques presented are performed for vector fields on the sphere depending on the distance, magnitude and spectral type and can also be applied to the vector field of the individual motions for each catalog.

Name : MARTIN-MUR Tomas

Institut : Caltech/JPL

Co-Authors : T. Martin-Mur, J. Lazio, S. Bhaskaran, R. Park, C. Jacobs

Type of presentation : ORAL

Country : USA

Title : Leveraging Gaia Data for Deep Space Navigation

Abstract : Star catalogs and solar system body ephemerides have been used over the years to determine the trajectories of spacecraft across the Solar System. Optical images of the position of natural bodies against the star background can be used to determine the position of the spacecraft taking the image either in inertial space or relative to the imaged body. Optical navigation was used during the planetary flybys of the Voyager spacecraft, was also used by the Galileo mission to tour the Jovian system and by Cassini mission to tour the Saturnian system, and Deep Space 1 demonstrated using asteroid images to perform cruise navigation across the Solar System. The increased accuracy and number of objects provided by Gaia’s star catalog can be used to more precisely and reliably navigate spacecraft across the Solar System. The development of interplanetary optical communications opens new possibilities: in addition to improving the accuracy of optical navigation using images taken by spacecraft, Gaia’s dense and accurate catalog can also be used to perform ground-based astrometry of spacecraft equipped with an optical communications terminal. The laser used to transmit data to the ground can also be imaged against the background of stars to determine the plane-of-sky position of the spacecraft, with accuracy, under the right conditions, similar to that provided by VLBI tracking. When compared with radiometric tracking, ground optical imaging has the advantage of not being affected by charged particle effects, but the disadvantage of requiring dark, clear skies. This talk will discuss the uses of the Gaia catalog for deep space navigation and the advantages and disadvantages of using optical and near-optical frequencies when compared with radio-frequency tracking.

Name : MARTíNEZ María J.

Institut : Universidad Politècnica de Valencia

Co-Authors : M.J. Martí­nez, F.J. Marco

Type of presentation : POSTER

Country : SPAIN

Title : A REVISION OF ΔT AND LOD VALUES FOR THE V, VI AND VIITH CENTURIES

Abstract : Studies of pretelescopic values of ΔT have been arranged by many authors. Ancient observational records of total and annular solar eclipses and in a lesser extend also lunar eclipses and occultation have been used to provide limits to the value of ΔT. We provide a first approximation for computed values of ΔT from the Vth to the VII th century considering all the available ancient astronomical records, paying special attention to those from Western Europe for which a new analysis and reduction has been carried out. The results obtained in the first instance corroborate those obtained by Soma and Tanikawa in the sense that the ΔT for these centuries seems to be significantly lower than that obtained by other studies.

Name : MIGNARD Francois

Institut : Université Côte d'Azur, Observatoire de la Côte d'Azur

Type of presentation : ORAL

Country : FRANCE

Title : Optical CRF from Hipparcos to Gaia: a tribute to Jean Kovalevsky

Abstract : We all witnessed great progress in the realisation of Celestial Reference Frame in the optical domain with the advent of space astrometry and the successul achievements of Hipparcos and Gaia. I will come back to the evolution of the field from the Hipparcos proposal in the early 1980s to the expected situation when Gaia complete its mission. The talk is dedicated to the late Jean Kovalevsky whose action was so decisive in the emergence of space astrometry and his key role and scientific career will be reminded.

Name : MOVSESIAN Pavel

Institut : Saint Petersburg State University

Co-Authors : P. Movsesian, S. Petrov, D. Trofimov, I. Chekunov

Type of presentation : POSTER

Country : RUSSIAN FEDERATION

Title : Analysis and normalization of GNSS onboard clocks

Abstract : Nowadays determination of precise coordinates using GNSS (Global Navigation Satellite System) observations can be made with differential method or with absolute solution (PPP method – Precise Point Positioning). Precision of navigational data, such as satellite ephemerides and satellite clock biases, is very important when using PPP method. Usually satellite orbits are approximated with smooth functions, currently their accuracy is about 2-3 cm. Unlike ephemerides satellite clock biases are not approximated with any function, also clock series are being processed not as a continuous time series but as daily fragments, which leads to jumps at 00:00 UTC. Processing methods that are currently used can also lead to clock jumps inside a day. Analysis of clock biases lead us to the conclusion that the aforementioned jumps don’t represent real clock behaviour. They are a result of incorrect processing methods. Other researchers also come to this conclusion. Different studies propose a variety of satellite clock improvement methods but clock jump removal is performed manually. This is an obstacle for large data array processing. We propose an automatic jump correction algorithm. Determination of quadratic trend and Kalman filter are employed by other methods in some way or another. Besides that we assume existence of some additional linear trends that were not properly processed originally. We processed about two years of satellite clock biases. Use of our algorithm allows removal of clock jumps on time intervals of any length.

Name : NAGHIBI Elnaz

Institut : Imperial College London

Co-Authors : S. E. Naghibi, S. A. Karabasov

Type of presentation : ORAL

Country : ENGLAND

Title : Excitation of the Earth’s Chandler wobble by the North Atlantic double-gyre

Abstract : We investigate the effect of the North Atlantic double-gyre on Chandler wobble excitation. To this end, we calculate the motion terms of the Chandler wobble excitation for the North Atlantic region using two different ocean models: i) a quasi-geostrophic double-gyre model in an idealized quadrangle domain with steady wind forcing and ii) HYCOM (HYbrid Coordinate Ocean Model) simulations with realistic continent boundaries and time dependent wind forcing. We analyze the discrepancies between the resulting excitation of the two models and discuss how differences in the models’ assumptions can result in different predictions of Chandler wobble excitation. Finally, to compare the contribution of the North Atlantic with that of global oceans, we verify the predicted excitation with geodetic observation of the Chandler wobble after subtraction of mass terms estimated from GRACE (Gravity Recovery and Climate Experiment) satellite gravimetry data.

Name : NASTULA Jolanta

Institut : Centrum Badan Kosmucznych PAN

Co-Authors : J. Nastula and J. Śliwińska

Type of presentation : ORAL

Country : POLAND

Title : Prograde and retrograde terms of gravimetric polar motion excitation estimates from the newest GRACE gravity field models

Abstract : The objective of this study is to consider what the newest Gravity Recovery and Climate Experiment (GRACE) solutions might contribute to the understanding of hydrological signal in polar motion excitations as observed by space geodetic techniques. The study also aimed to identify the solutions that best match geodetic observations of polar motion in specific spectral bands. In contrast to the previous works, here, the equatorial components of polar motion excitation functions (χ1 and χ2) are decomposed into prograde and retrograde time series by applying Complex Fourier Transform Models. We compare the reference hydrological signal in observed polar motion excitations (geodetic residuals) with (1) hydrological gravimetric excitation functions from the GRACE solutions (CSR RL05 and RL06, JPL RL05 and RL06, GFZ RL05 and RL06, ITSG 2016 and ITSG 2018, CNES RL03 and RL04) and from (2) the hydrological model LSDM with sea-level angular momentum SLAM added (LSDM + SLAM). Our general remark is that the new GRACE solutions provide better agreement with observed polar motion excitation than the previous solutions. Moreover, the consistency between different solutions has been increased. However, despite improved correlation agreement with reference data, there is still no satisfactory amplitude compatibility. The choice of the GRACE solution which best match geodetic observations depends on the oscillation considered.

Name : NICKOLA Marisa

Institut : HartRAO

Co-Authors : M. Nickola, A. de Witt, J. Quick, C.S. Jacobs, D. Gordon

Type of presentation : POSTER

Country : SOUTH AFRICA

Title : Improving HartRAO performance at K-band

Abstract : A K-band (24 GHz) celestial reference frame (CRF) of more than 900 sources covering the full sky has been constructed using over 0.6 million observations from more than 70 observing sessions from the VLBA and HartRAO-Hobart. In the north, the VLBA is able to observe declinations of +90 to -40 deg. In the south, the HartRAO-Hobart baseline is currently the only baseline regularly observing the southern sky at K-band for CRF development, covering declinations from -90 to +0 deg. Southern K-band CRF observations will benefit most from improving the baseline sensitivity and increasing the data recording rate. The baseline sensitivity has been greatly improved by the inclusion of the Tidbinbilla 70-m antenna in a first successful HartRAO-Tidbinbilla K-band session at the beginning of 2019. Digital back-end enhancements should allow for recording at a data rate of 4 Gbps in the south in the near future. One of the highest priorities for the HartRAO 26-m antenna, is to update the current pointing model. Further envisaged improvements for the HartRAO 26-m antenna that should improve K-band sensitivity in the south include an upgrade to the sub-reflector to allow for active-focusing, the replacement of ageing and failing encoders and re-alignment of surface panels. The additional baselines that may be provided by future HartRAO-Hobart-Tidbinbilla sessions, should allow for isolating pointing issues to a particular antenna.

Name : NURUL HUDA Ibnu

Institut : Observatoire de Paris

Co-Authors : I. Nurul Huda, C. Bizouard, S. Lambert, and Y. Ziegler

Type of presentation : POSTER

Country : FRANCE

Title : Estimation of Earth rotation resonance parameters through VLBI analysis

Abstract : The VLBI observations enable the investigation of the Earth rotation resonances in the retrograde diurnal band with respect to a terrestrial frame, associated with the Free Core Nutation (FCN), the Free Inner Core Nutation (FICN), and the common polar motion. The resonance parameters (period and quality factor) determine the frequency transfer function $T(\sigma)$ from the theoretical luni-solar nutation terms $\eta_R(\sigma)$ of a rigid Earth to the nutation terms observed by VLBI $\eta(\sigma): \eta(\sigma) = T(\sigma) \eta_R(\sigma)$. Therefore they can be obtained by inverting the former relations constituted by a set of observed and theoretical nutation terms. We revisit this problem by considering 40 years of VLBI observations and more complete atmospheric-oceanic non-tidal perturbations, that have to be removed from the observed nutation terms before inversion. The inclusion of the complete atmosphere and ocean correction produce a significant change of the FCN quality factor and FICN parameters. On the other hand the nutation analysis allows us to investigate the frequency dependence of the polar motion resonance in the diurnal band: for the retrograde nutation terms close to 18.6 years, the polar motion period is close to 396 days, and for nutation terms around 13.66 days, the analysis leads to a period of 383 days.

Name : PARK Han Earl

Institut : KASI

Co-Authors : H.-E. Park, K.-M. Roh, S.-M. Yoo, J. Cho

Type of presentation : POSTER

Country : SOUTH KOREA

Title : The Development of the GNSS-based Products Service System

Abstract : The Korea Astronomy and Space Science Institute (KASI) is developing a GNSS-based products service system, which regularly generates station positions, orbits, earth orientation parameters (EOP), and the analysis results, in order to utilize it in the Earth system research and the development of the Korean Positioning System (KPS). The service system consists largely of the Data Processing Server (DPS) and the Data Receive and Service Server (DRS). The DPS carries out data processing and data analysis with the Position and Navigation Data Analyst (PANDA) software, where various GNSS products are generated. The DRS collects data necessary for processing data, such as RINEX files, and serves the GNSS products. In this poster, the configuration of the GNSS-based products service system is introduced and several analysis results for the GNSS products are explained.

Name : PASHKEVICH Vladimir

Institut : Central (Pulkovo) Astronomical Observatory of Russian Academy of Sciences

Co-Authors : V.V.Pashkevich, A.N.Vershkov

Type of presentation : ORAL

Country : RUSSIA

Title : Geodetic (Relativistic) rotation of the Mars satellites system

Abstract : In this study the relativistic effects (the geodetic precession and the geodetic nutation, which are composing the effect of the geodetic rotation) in the rotation of Mars satellites system for the first time are investigated. The most essential terms of the geodetic rotation are found by means of the algorithm of Pashkevich (2016), which is applicable to the study of any bodies of the Solar system that have long-time ephemeris. As a result, in the perturbing terms of the physical librations and in Euler angles for Mars satellites (Phobos and Deimos) and in Euler angles for Mars the most significant systematic and periodic terms of the geodetic rotation are calculated. The reported study was funded by RFBR according to the research project 19-02-00811.

Name : PASHKEVICH Vladimir

Institut : Central (Pulkovo) Astronomical Observatory of Russian Academy of Sciences

Co-Authors : A.V.Melnikov, V.V.Pashkevich, A.N.Vershkov and G.M.Karelin

Type of presentation : POSTER

Country : RUSSIA

Title : Chaos and relativistic effects in the rotational dynamics of minor planetary satellites

Abstract : The chaotic regime of rotation of minor planetary satellites taking place during tidal evolution is considered. The possibility of the formation of strange attractors in the rotational dynamics of all known minor planetary satellites of the Solar system is estimated. A detailed analysis of the presence of anisotropy in the orientation of the satellite figure during its chaotic rotation was carried out. The relativistic effect (the geodetic precession, which is the part of the effect of the geodetic rotation) in the rotation of some minor satellites for the first time is investigated. As a result, in Euler angles, the most significant systematic terms of the geodetic rotation are calculated. The reported study was funded by RFBR according to the research project 19-02-00811.

Name : PASYNOK Sergey

Institut : VNIIFTRI

Co-Authors : S. Pasynok, I. Bezmenov, I. Ignatenko, Tcyba E.N.

Type of presentation : POSTER

Country : RUSSIAN FEDERATION

Title : Operative EOP activities in VNIIFTRI

Abstract : VNIIFTRI as the Russian Main Metrological Center of Time, Frequencies and Earth Rotation Service carried out the rapid EOP processing based on GNSS, VLBI and SLR observations for many years. VNIIFTRI takes participation in GNSS and SLR observations of IGS and ILRS too. The EOP activities at VNIIFTRI can be grouped in four basic topics: 1) Processing GNSS, SLR and VLBI observation data for EOP evaluation; 2) Evaluation of combined EOP values based on EOP series and SINEX combination; 3) Combination of GLONASS satellites orbit/clock; 4) Providing GNSS and SLR observations at five metrological sites acting under the auspices of VNIIFTRI. The processing of GNSS, SLR and VLBI observations is currently executed with the help of modern application program packages such as BERNESE GNSS software and ARIADNA software that were properly adapted to the rapid service mode. Combining daily EOP are calculated in VNIIFTRI by means the combination of the eight independent individual EOP series provided by four Russian analysis centers. The SINEX daily combination is provided too. The operative orbit/clock combination is carried out. GNSS observations on the five metrological sites are carried out permanently and hourly files are formed. The results of observations are collected in Russian Main Metrological Center . SLR observations are carried out at Mendeleevo and Irkutsk.

Name : PAVLIS Erricos

Institut : Joint Center for Earth Systems Technology, Univ. of Maryland, Baltimore County

Co-Authors : E. C. Pavlis, V. Luceri, M. Kuzmicz-Cieslak, and G. Bianco

Type of presentation : ORAL

Country : UNITED STATES

Title : The ILRS Planned Contribution to ITRF2020

Abstract : The ILRS Analysis Standing Committee (ASC) has been working towards the development of a vastly improved contribution of the SLR technique in the development of the next ITRF. The ASC has completed the re-analysis of the modern-era data set with improved modeling and the newly adopted approach for “systematic error”-free results. This re-analysis incorporates an improved “target signature” model (CoM) that allows better separation of true systematic errors at each tracking system from errors in the model describing the target’s signature for the particular system. The new modeling results in improved TRF attributes that are reflected in the time series of the TRF origin and scale. The new approach will be used for future ITRF model developments. The ASC devoted all its efforts to develop, evaluate and implement the new approach that will continuously monitor the systematic errors at all ILRS sites in the network. Following these developments, the ILRS operational products are based on our best knowledge of the ground system behavior and performance. The presentation will demonstrate the level of improvement with respect to the previous ILRS product series and a glimpse of what we should expect after the development of ITRF2020.

Name : PAVLOV Dmitry

Institut : Institute of Applied Astronomy

Co-Authors : D. Pavlov

Type of presentation : ORAL

Country : RUSSIA

Title : Solid body tides in the dynamical model of the Moon

Abstract : The current dynamical model of the Moon, used to build lunar-planetary ephemeris, is based on lunar laser ranging data (LLR) and GRAIL lunar gravimetry data. The model includes core-mantle friction, rotational dissipation, and tidal dissipation with a single delay, frequency-unaware. It is well known that the current model does not explain every observable signature in the rotation. There are three additional (kinematic) periodic terms well determined from LLR. There is also a nonzero S21 coefficient of lunar gravitational field, probably indicating another effect in the rotation still unaccounted for in the dynamical model. A possible extension to the dynamical model of the lunar tides, aiming to build a better approximation of the lunar non-rigid effects, is presented.

Name : PEREPELKIN Vadim

Institut : Moscow Aviation Institute

Co-Authors : V. Perepelkin, S. Krylov, A. Filippova

Type of presentation : POSTER

Country : RUSSIA

Title : DYNAMIC EFFECTS OF THE SPATIAL MOVEMENT OF THE EARTH-MOON SYSTEM IN THE EARTH’S POLE OSCILLATION

Abstract : On the basis of a numerical-analytical approach, the irregular effects of the oscillatory process of the Earth's pole, associated with changes in the Chandler and one-year component, are investigated. An approach to the study of oscillatory processes in the motion of the Earth's pole is proposed on the basis of joint consideration of the Chandler and one-year components of its motion. Within the framework of this approach, a transformation to a new coordinate system has been found, in which the in-phase motion of the pole and the precession of the lunar orbit are shown. Achievement of high accuracy of forecasts is associated with various disturbing factors that allow to analyze subtle effects in the oscillatory process of the earth's pole on a qualitative level. In the framework of the celestial mechanical formulation of the spatial variant of the problem "deformable Earth-Moon in the field of attraction of the Sun", the existence of the found oscillatory process with small amplitudes is shown. With the help of numerical-analytical modeling, the possibilities of identifying the parameters of the oscillations of the Earth's pole and the approximation of the extended model to the data of the International Earth Rotation and Reference Systems Service are considered. The estimates of the accuracy of the prediction of the coordinates of the Earth's pole are given, taking into account the additional terms caused by the lunar perturbation.

Name : PETROV Leonid

Institut : NASA Goddard Space Flight Center

Co-Authors : L. Petrov, R. Ray

Type of presentation : ORAL

Country : USA

Title : Combined analysis of free and forced nutations from VLBI group delays

Abstract : We revisit parameterization of Earth's nutation determined from VLBI group delays. The main goals of our study are (a) to obtain improved and self-consistent estimates of compliances that describe the response of the non-rigid Earth to external torques and geophysical excitations, along with realistic error estimates; (b) to close the budget of the excitation and dissipation of the FCN or to establish that the budget cannot be closed within uncertainties of geodetic observations. Our primary geodetic data are Very Long Baseline Interferometry (VLBI) group delays. This is achieved by (1) incorporating into our data analysis the non-gravitational forcings from the latest advanced tidal and non-tidal oceanic models and atmospheric models; (2) improving the ocean tide model at psi1 tide (critical because its frequency is so close to the NDFW frequency); and (3) estimating parameters of the nutation transfer function directly from VLBI group delays without resorting to intermediate time series. Preliminary results of the study are presented.

Name : PITJEVA Elena

Institut : Institute of Applied Astronomy of Russian Academy of Sciences

Co-Authors : E. V. Pitjeva, N. P. Pitjev, D. A. Pavlov

Type of presentation : ORAL

Country : RUSSIA

Title : Estimates of changes of the gravitational constant G and the gravitational parameter of the Sun GM_Sun based on new data and observations of spacecraft and on updated the EPM2019 ephemeris

Abstract : New planetary ephemeris EPM2019 has been built using data and observations for spacecraft and a refined dynamic model of the solar system. In the dynamic model, new mass estimates were obtained for the Main asteroid belt (for large bodies and a total mass estimate for small asteroids, debris and dust) using a new discrete model. A similar refinement was made for the Kuiper belt. The dynamic model includes the total influence of two numerous and compact groups of Jupiter Trojans L4 and L5. The new version of the EPM ephemeris takes into account the Lense-Thirring relativistic effect, which is especially important for Mercury and Venus. Observational data include the high-precision measurements, obtained relatively recently by the MESSENGER (Mercury orbiter) and Juno (Jupiter orbiter), as well as updated data of Odyssey and MRO (Mars orbiters) till the end of 2017. This allowed us to obtain a new estimate of the change of the gravitational parameter of the Sun GM_Sun. In addition, estimates of the mass loss of the Sun were obtained taking into account data from the Ulysses spacecraft (1992--2009) for the solar wind, averaged over the solar cycle. With those estimates taken into account, new upper and lower bounds were found on the change in the gravitational constant G.

Name : PUENTE Víctor

Institut : National Geographic Institute of Spain

Co-Authors : V. Puente, M. Folgueira, E. Azcue

Type of presentation : ORAL

Country : SPAIN

Title : Analysis of VLBI and GNSS ties in CONT campaigns

Abstract : Every three years, the International VLBI Service for Geodesy and Astrometry (IVS) manages CONT campaigns to acquire continuous VLBI data during 15 days. One of the purposes of these campaigns is the inter-technique comparison of VLBI products with other space geodesy techniques. In this work, VLBI estimates of Earth Orientation Parameters (EOP), station coordinates and troposphere Zenith Total Delays (ZTD) are compared to those estimated by means of Global Navigation Satellite Systems (GNSS) observations, considering different invididual and combined solutions for all CONT campaigns to date (CONT02, CONT05, CONT08, CONT11, CONT14 and CONT17).

Name : PUENTE Víctor

Institut : National Geographic Institute of Spain

Co-Authors : E. Azcue, V. Puente, S. Garcia-Espada, Y. Garcia-Espada, P. A. Vaquero

Type of presentation : POSTER

Country : SPAIN

Title : Status of the geodetic VLBI analysis at the National Geographic Institute of Spain

Abstract : National Geographic Institute of Spain has been very involved in the last decades in the technical aspects of geodetic VLBI and in the development of RAEGE project, for an Atlantic Network of Geodynamical and Space Stations. As a complement of these activities, a geodetic VLBI analysis team has been set up. The purpose of this contribution is to present the different activities carried out by the analysis team, regarding historical reprocessing of VLBI data using different software packages and the study of gravity deformation in Yebes radiotelescope.

Name : RAMBAUX Nicolas

Institut : IMCCE

Co-Authors : Nicolas Rambaux, Vishnu Viswanathan, Agnes Fienga, Jacques Laskar, Mickael Gastineau

Type of presentation : ORAL

Country : FRANCE

Title : Dynamical model of lunar core and observational constraint from Lunar Laser Ranging

Abstract : Our Moon is one of the most studied objects in the Solar system; we benefit from chemical, geophysical, and geodetical observations achieved by multiple Earth ground based telescopes and in situ missions. However, its deep interior properties remain a puzzle because the lunar core is very small implying weak signature in the observational data set. This paper focuses on the description of a new lunar core rotational model included in INPOP and used to provide a determination of the radius and geometry of the lunar core-mantle boundary (CMB) from the LLR observations. The obtained CMB radius is in full agreement with one seismological model

Name : RAUT Shrishail

Institut : Chair of Space Technology, Technische Universität Berlin

Type of presentation : POSTER

Country : GERMANY

Title : Effect of VLBI intensive sessions on daily and sub-daily ERP determined from CONT17 IVS data.

Abstract : This work deals with combining IVS (International VLBI Service for Geodesy and Astrometry) 1-hourly Intensive sessions and 24-hour sessions. We investigate the effects on the polar motion and UT1-UTC, which constitute the Earth Rotation Parameters (ERP). Sessions from the CONT17 campaign are chosen as they provide continuous VLBI observations over two weeks (28th Nov - 12th Dec 2017) of currently highest quality. For the standard 24-hour sessions in this campaign, two different legacy networks are involved, namely VLBA and IVS networks. Two intensive sessions take place in addition to the two 24-hour sessions every day. The intensives are combined with the 24-hour sessions at the normal equation level (NEQ) utilizing the global solution module of Vienna VLBI software at GFZ (VieVs@GFZ). The analysis is performed on the daily and sub-daily scales to quantify how intensives affect the ERP on different temporal resolutions. Furthermore, spectral analysis of the ERP estimates helps determining changes due to the intensive session combinations. Finally, , the VLBI results are compared at daily and sub-daily resolutions with the estimates obtained from the global navigation satellite systems (GNSS) analysis.

Name : RICHARD Jean-Yves

Institut : Observatoire de Paris - SYRTE - UMR CNRS 8630

Type of presentation : POSTER

Country : FRANCE

Title : Earth Orientation Parameters by GNSS & VLBI
COMBINATION at Normal Equation Level

Abstract : The Earth Orientation Parameters (EOP) - namely pole coordinates (x,y), difference UT1 - UTC, and precession-nutation corrections (dX,dY) w.r.t. IAU200A/2006 model - are determined on a daily basis by IERS Earth Orientation Centre (located at Observatoire de Paris/SYRTE) through combination of intra-technique EOP solutions. In parallel the Earth Orientation Center actively develops a multi-technique combination at normal equation level. Now, this combination is operated for data obtained by Global Navigation Satellite Systems (GNSS) and Very Long Baseline Interferometry (VLBI). It allows us to estimate in one run the EOP on a daily basis, the displacements of the stations constituting the terrestrial frame (TRF) on a weekly basis, and possibly the invariable coordinates of the quasars constituting the celestial frame (CRF). First results indicate that GNSS/VLBI combination permits to significantly decrease the correlation between EOP parameters.

Name : ROBERT Vincent

Institut : IMCCE - Observatoire de Paris - IPSA

Co-Authors : V. Robert, J. Desmars, J.-E. Arlot

Type of presentation : ORAL

Country : FRANCE

Title : The NAROO digitization centre

Abstract : Several hundred thousand photographic plates were made between 1890 and 1998, in all observatories of the World, before their production stopped to be gradually replaced by CCDs. It's a huge observation tank, especially that we know that only a tiny part was analyzed with former methods, and the results published and used for validation of dynamic or physical models. Some of these results are still in use today: these are observational data for which the time parameter is essential to describe the evolution of systems. The recent arrival of Gaia-DR2 catalog provided a new interest in the analysis of old observations : that of old astrophotographic plates. Because "former" star catalogs did not allow us to measure with a high accuracy observations made before the 60's, Gaia-DR2 references and data moves back this limitation. All solar system objects observed in the past could now be worth to (re-)reduce, to provide new accurate positioning data. For that purpose, Paris Observatory set up a new sub-micrometric digitizer to produce high accurate astrometric images. Moreover, this machine is able to digitize most of the different kind of plates for other scientific goals. In our presentation, we will present the NAROO facilities, machine and progress. We will detail our purpose, project and deadlines for digitizing plate collections of several observatories and institutes.

Name : ROCCA VOLMERANGE Brigitte

Institut : Institut d'astrophysique de Paris

Co-Authors : B. Rocca-Volmerange, L. Godinaud

Type of presentation : ORAL

Country : FRANCE

Title : Continuous UV to far-IR Spectral Energy Distributions of Quasars 

Abstract : Synthetic templates of QSOs and galaxies are proposed on the similar continuous wavelength coverage (10 to 10^7 AA: UV-farIR) defined by the new evolutionary code Pegase.3. Colors of QSOs and galaxies through the Gaia, WYSE and JWST instruments are predicted at various redshifts. These libraries are built for multiple objectives: dust properties (attenuation, scattering, emission), QSO-galaxy host correlations, by using best-fitting procedures on multi wavelength observations.

Name : ROLAND Jacques

Institut : IAP

Co-Authors : Roland, Gattano, Lambert & Taris

Type of presentation : ORAL

Country : FRANCE

Title : Structure and variability of quasars

Abstract : We will show how one can explain the variations of the time series of the source 2201+315 knowing the structure and the variability of its nucleus. More generally we will show how the structure and variability of quasars can produce the variations of the time series of geodetic observations.

Name : RON Cyril

Institut : Astronomical Institute CAS

Co-Authors : Y. Chapanov, C. Ron, J. Vondrák

Type of presentation : POSTER

Country : CZECH REPUBLIC

Title : Chandler period variations due to solar activity

Abstract : The Chandler wobble (CW) is a free rotational mode of the Earth associated with its dynamical ellipticity. In the absence of an external force, the CW would have a period of 430 days. The Chandler wobble is excited by a combination of atmospheric and oceanic processes, with the dominant excitation mechanism being ocean‐bottom pressure fluctuations, caused by ocean circulation and variations in temperature, salinity, and winds. The most important energy sources of all atmospheric and oceanic processes are the solar activity cycles, so the solar cycles affect climatic system and angular momentum of atmosphere and ocean, followed by polar motion and Chandler period variations. The Chandler period variations are determined from the coordinates of polar motion for 1860-now from the solution C01 of the IERS. The centennial, decadal and interannual harmonics of solar activity are determined by the Method of Partial Fourier Approximation of time series of the Total Solar Irradiance (TSI), Sunspot Numbers (SSN) and North-South Solar Asymmetry (N-S SA). The long-term variations of CW period are compared with corresponding cycles of N-S SA. The decadal and interannual oscillations with periods above 6yr of CW have good agreement with the TSI cycles in several frequency bands. The short-term CW oscillations have good agreement with SSN cycles in two bands of periodicity between 3 and 4 years. It is remarkable that the CW grand minimum around 1930 is strongly connected with all solar harmonics with dominating influence of long term N-S SA variations (periodicity 78-156yr, CW period decrease - 6d) and TSI variations (periodicity 39-52yr, CW period decrease - 10d). The TSI influence on CW period variations is non-linear and frequency dependent. The value of CW period increases during the warming cycles of solar activity and decreases during some solar minima.

Name : ROSAT Severine

Institut : IPGS-EOST

Co-Authors : S. Rosat, N. Gillet, J.-P. Boy

Type of presentation : ORAL

Country : FRANCE

Title : On the possible detection of inter-annual deformation signal at the Earth's surface due to the fluid core dynamics

Abstract : The dynamical fluid core powers the Earth's magnetic field. Fluid flows at the Earth's core surface are usually reconstructed from geomagnetic data, particularly from secular variations of the magnetic field. Fluid core motions induce changes in the fluid pressure acting at the core boundaries. We consider the possibility for a signature at the Earth’s surface of interannual deformations due to core flows. In particular, we will consider signals of period around 6-year, which are observed in both length-of-day (LOD) variation data (Abarca del Rio et al. 2000) as well as in GNSS observations (Ding & Chao, 2018). The 6-year oscillation in LOD series is associated with the propagation of torsional Alfven waves within the fluid core (Gillet et al. 2010). One possible triggering mechanism is associated with the solid inner core libration under a gravitational coupling between the solid inner core and the mantle (e.g. Davies et al. 2014). Potential relations with geomagnetic jerks have been drawn (Holme & de Viron 2013), although we know interannual magnetic field changes originate primarily from non-axisymmetric core fluid motions (e.g. Finlay et al, 2016). As such, interannual signals in GNSS series would more likely be the consequence of non-axisymmetric flows, and questions on a potential relation between these and torsional waves.

Name : SALSTEIN David

Institut : Atmospheric and Environmental Research

Type of presentation : ORAL

Country : USA

Title : Atmospheric angular momentum related to Earth rotation studies: history and modern developments

Abstract : It was noted some time ago that the angular momentum of the atmosphere varies, both regionally as well as in total. Given the conservation of angular momentum in the Earth system, except for known external torques, such variability implies transfer of the angular momentum across the atmosphere’s lower boundary. As nearly all is absorbed by the Earth below, the solid Earth changes its overall rotation from this impact. Due to the large difference between in the moments of inertia of the atmosphere and Earth, relatively big differences in the atmosphere are translated as relatively very small differences in the Earth, measurable as changes in Earth rotation rate, and polar motion. The relative atmospheric angular momentum (AAM), is that due to the motion of the winds and to the changes in mass distribution, closely related to the atmosphere pressure patterns; its variability in the atmosphere is mirrored in the Earth rotation rate and polar motion. This connection between the global solid Earth properties and the global and regional atmosphere on a number of time scales, especially seasonal and interannual, was much appreciated by Barbara Kolaczek, with Jolanta Nastula, at the Space Research Center in Warsaw, and this was a subject of our collaborative studies. Many calculations were made of atmospheric angular momentum, leading to a service under the Global Geophysical Fluids Center of the IERS based on calculations using both operational meteorological series, determined for weather forecasting purposes, and retrospective analyses of the atmosphere. Theoretical development of the connection between the AAM, Earth rotation/polar motion, and also the angular momentum of the other geophysical fluids occurred at the same time that space-based observations and enhanced computer power were allowing improved skills for both weather analysis and forecasting. Hence better determination of the AAM became possible, which could be used as a measure for forecasting Earth rotation. Today we are looking at the atmosphere in combination with the ocean and other fluids, and also assessing the implications of climate variability on Earth rotation through climate model research. According to models of the Earth system, significant changes in winds appear to be a possible result of climate change, with implications for the Earth rotation parameters.

Name : SECREST Nathan

Institut : U.S. Naval Observatory

Co-Authors : N. Secrest, J. Frouard

Type of presentation : ORAL

Country : USA

Title : Quasar Selection Techniques going into the Gaia Era

Abstract : Quasars, galaxies bolometrically dominated by the emission from their active galactic nuclei, are of profound importance to multiple areas of astrophysics. Not only do quasars inform our understanding of the deep relationship between supermassive black holes and their host galaxies, they also define a quasi-static reference frame that make them an ideal realization of the International Celestial Reference System (ICRS). Key to the utilization of quasars for reference frame work has been the advent of large, all-sky surveys, especially Gaia with its unprecedented astrometric precision at visual wavelengths. In this talk, I will discuss the advancements in quasar selection techniques made in recent years, and new avenues of research into overcoming our current observational limitations.

Name : SIDORENKOV Nikolay

Institut : Hydrometcenter of Russian Federation

Co-Authors : N, Sidorenkov, E. Dionis, C. Bizouard, L. Zotov

Type of presentation : ORAL

Country : RUSSA

Title : Decade fluctuations in Earth's rotation as evidences of lithospheric drift over the asthenosphere

Abstract : The decadal instabilities in Earth's rotation (DIER) are thought to be caused by the interactions between the Earth's core and its mantle. This hypothesis successfully explains why there is a close correlation between DIER and the variations in the rate of the westward drift of the geomagnetic eccentric dipole, since it is successfully reproduced by modeling of the redistribution of the angular momentum between the fluid core and the mantle of the Earth. However, the hypothesis can not explain the close correlations of DIER: with the observable variations in the masses of the Antarctic and Greenland ice sheets; with the decade oscillations of the types of synoptic processes (i.e. the epochs of the atmospheric circulation); with the anomalies of the global temperature; and with regional anomalies of the cloudiness, precipitations, and other climatic characteristics. An alternative to the core-mantle interaction hypothesis is presented here. This alternative hypothesis claims that the DIER are actually caused by fluctuations in the angular velocity of lithospheric drift over the asthenosphere. The sliding of the lithosphere over the asthenosphere is possible due to of the vibrational displacement mechanism produced by tidal forces. The lithospheric plates exhibit vibrational displacements over the asthenosphere in the horizontal direction by shear stresses caused by friction, wind, and ocean currents. There is abundant evidence supporting this lithospheric drift model

Name : SKURIKHINA Elena

Institut : IAA RAS

Type of presentation : POSTER

Country : RUSSIA

Title : ESTIMATION OF THE ACCURACY OF PREDICTION OF THE EARTH ORIENTATION PARAMETERS AT THE IAA DATA ANALYSIS CENTER

Abstract : The prediction of the parameters of the Earth's rotation (ERP) is especially important in the operational and super-operational determination of the ERP. The Data Analysis Center of IPA RAS uses its own ERP forecast, which was developed and tested for the IAA ERP service in 1996. Since then, only minor changes have been made regarding the nutation forecast (and the coordinates of the celestial pole). The algorithm is distinguished by high reliability and acceptable forecast quality. The accuracy of the prediction has not been evaluated since its introduction into the ERP service. In this regard, in the light of the increasing requirements for the accuracy of determining the EOP, it has become necessary to estimate the real accuracy of the forecast used. In the work, the accuracy of the prediction of the ERP for the IERS C04 and finals series used in the IAA is estimated.

Name : SPOTO Federica

Institut : Observatoire de la Côte d'Azur

Co-Authors : F. Spoto, P. Tanga

Type of presentation : ORAL

Country : FRANCE

Title : Asteroid astrometry in the Gaia era

Abstract : Gaia data release 2 (DR2) represents a real revolution in our understanding of asteroid astrometry. For the first time, Gaia DR2 contains almost 2 000 000 observations of 14 099 Solar System Objects with a sub-mas accuracy for the brightest asteroids. On the other side, the use of the DR2 stellar catalogue allows the observers to produce accurate measurements of asteroid positions, of the order of a few tens of mas, unthinkable before Gaia. We present an accurate and complete analysis of the asteroid post-fit residuals, analysing the performances of each observatory, per catalogue used in the reduction, year of observation and magnitude of the object. In particular, we will also give an overview of the main asteroid surveys used for discovery of near-Earth asteroids. We then compare the typical accuracy of ground-based observatories to the one of Gaia DR2 asteroid observations, showing the main improvements due to Gaia and the applications in the study of the Solar System.

Name : TANGA Paolo

Institut : Observatoire de la Côte d'Azur

Co-Authors : P. Tanga

Type of presentation : ORAL

Country : FRANCE

Title : Correcting archive asteroid astrometry by Gaia DR2

Abstract : As shown in the past, differences in zonal errors in old astrometric catalogs are at the origin of large residuals and poor statistical properties in the orbit computation of asteroids, whose astrometry has been calibrated by such catalogs. The increase in astrometric accuracy brought by the Gaia mission of ESA is the source of new challenges for the correct computation of improved asteroid orbits, especially when astrometric measurements reduced with previous catalogs are included. We explain a new approach to debiasing, devoted to the mitigation of zonal error in the available pre-Gaia asteroid astrometry.

Name : TCYBA Efim

Institut : FSUE VNIIFTRI

Co-Authors : E. Tcyba, O. Volkova

Type of presentation : POSTER

Country : RUSSIAN FEDERATION

Title : Determination of Earth Orientation Parameters by SLR in MMC SSTF FSUE VNIIFTRI

Abstract : In 2014, MMC SSTF FSUE VNIIFTRI resumed work on the processing of SLR data (LAGEOS 1,2) to calculate the EOP. As the basic programming package the Bernese 5.2 software (Switzerland) was chosen, which has been upgraded with the aim of improving the accuracy of EOP determination. Additional program modules are written in Perl, Python and Matlab programming languages and can be used on both Windows OS and Linux, 32-bit and 64-bit platforms. The accuracy of determining the coordinates of the Earth’s pole by developed software is 0.08 - 0.1 mas. In 2017, a special software module for data post-processing was developed which allowed to increase the accuracy of EOP determination according to SLR and GNSS data by 12-20 % (tests were carried out on the data of FSUE VNIIFTRI, IAA (Institute of Applied Astronomy) and IAC (Information-Analytical Center of Russian Space Agency). Further improvement of accuracy is possible by increasing the amount of measurement information and increasing the frequency of EOP determination per day.

Name : TEYSSANDIER Pierre

Institut : SYRTE, Observatoire de Paris

Co-Authors : P. Teyssandier

Type of presentation : ORAL

Country : FRANCE

Title : Unified approach of Shapiro and lensing effects in the field of an axisymmetric spinning body

Abstract : The existence of two time transfer functions has been recently proved for the Schwarzschild-like space-times in the linearized, weak-field limit. We extend this analysis to the metric of any axisymmetric spinning body. The contributions of the mass and spin multipoles are given by elementary integrals which can be calculated with any symbolic computer program. The expressions thus obtained can be applied to astrometry, tests of gravity and gravitational lensing without the appearance of enhanced terms.

Name : TITOV Oleg

Institut : Geoscience Australia

Co-Authors : F. Shu (SHAO)

Type of presentation : ORAL

Country : AUSTRALIA

Title : Observations of radio stars with geodetic VLBI

Abstract : We run a set of VLBI experiments to observe accurate positions of several known radio stars including the 65-meter Tianma and 64-meter Parkes radio telescopes. One radio star HR 1099 was detected in S/X dual frequency observing mode, and two radio stars (UX Ari and HR132714) were detected with the phase-referencing observations in X-band. The best measured formal error is 0.25 mas for HR1099 proving a good quality of the VLBI observations. Combination of the new results with the legacy optical and radio astronomical data helps to improve the estimates of proper motion of the three radio sources. Radio star UX Ari shows a complicated motion presumably due to several hidden companions. More VLBI observations of optically bright radio stars are necessary to calibrate the Gaia DR2 mission parallax. We are planning more observations of optically bright radio stars in phase-reference mode using large VLBI facilities.

Name : TROFIMOV Dmitrii

Institut : Saint Petersburg State University

Co-Authors : D.A. Trofimov, S.D. Petrov, Y.A. Serov, I.V. Chekunov, S.S. Smirnov, K.V. Zheltova, O.A. Troshichev

Type of presentation : POSTER

Country : RUSSIA

Title : Total Electron Content over Vostok antarctic station

Abstract : Total Electron Content (TEC) is one of the most important parameters of the ionosphere for propagation of radio waves. TEC is now being routinely monitored by global GNSS networks almost everywhere on Earth except geomagnetic poles. In order to study TEC evolution near the southern magnetic pole, two series of GNSS observations were carried out at the Vostok Antarctic station. Every of the two series lasted about one year each, 2016 and 2018. The collected GNSS observatoins were processed with RTKLIB and GeNeSiS software packages. TEC was estimated both from code and phase observables. The resulting TEC time series were analysed and compared to the global TEC map. These results may potentionaly augment our knowledge about ionosphere structure and evoultion near the geomagnetic poles. As a continuation of this study a permanent GNSS receiver is considered to be installed at the Vostok Antarctic station.

Name : VONDRáK Jan

Institut : Astronomical Institute CAS, Prague

Co-Authors : J. Vondrak, C. Ron

Type of presentation : ORAL

Country : CZECH REPUBLIC

Title : DETERMINATION OF FCN PARAMETERS FROM DIFFERENT VLBI SOLUTIONS, CONSIDERING GEOPHYSICAL EXCITATIONS

Abstract : Different VLBI solutions of celestial pole offsets (CPO) are used to determine parameters (period and Q-factor) of Free Core Nutation (FCN). To this end, Brzeziński’s broad-band Liouville equations are numerically integrated to account for geophysical excitations (effects of the atmosphere, oceans and geomagnetic jerks are considered). Best-fitting values of FCN parameters are found by least-squares fit to observed CPO, corrected for the difference between the FCN parameters used in IAU 2000 model of nutation and newly estimated ones; MHB transfer function is used to compute these corrections.

Name : WINSKA Malgorzata

Institut : Warsaw University of Technology

Type of presentation : POSTER

Country : POLAND

Title : Improved geodetic-hydrological residual time series constrained by polar motion observations and geophysical models

Abstract : The mass transport occurring in the Earth has a large influence on the excitation of polar motion. However, determination of the accurate time series of geophysical Earth rotation excitations coming from atmosphere, ocean and land hydrology models is far from being completely explaining observed variations in polar motion. The major contributors to changes in the Earth’s rotation are atmosphere and ocean, but land hydrology is important as well. Current global water storage models differ significantly from one another and are unable to fully close the so called geodetical budget: the agreement between observed geodetic excitations on polar motion and geophysical ones. Here, we compare the effects of several hydrological excitation functions calculated by removing modelled atmospheric and oceanic effects from space observations of full polar motion excitations GAM (Geodetic Angular Momentum). We called that functions as geodetic-hydrological residual time series. The estimation of hydrological effects on Earth’s rotation differs when using one atmospheric (Atmospheric Angular Momentum – AAM) and one oceanic model (Oceanic Angular Momentum – OAM). The goal of this study is to build and objective criterion that justifies the use of one combination of AAM+OAM to estimate geodetic-hydrological residuals time series. To do that, we determine the quality of each series by making an estimation of their noise level, using a generalized formulation of the “ three cornered-hat” method. After that, we construct a combined GAM-(AAM+OAM) series, which the noise level of combined geophysical time series will be minimal. These geodetic residuals time series will be analyzed and compared with hydrological excitation functions determined from hydrological models and from Gravity Recovery and Climate Experiment GRACE satellite mission.

Name : YATSKIV Yaroslav S.

Institut : Main Astronomical Observatory

Type of presentation : POSTER

Country : UKRAINE

Title : On the consistency between local ties and space geodesy estimates in the Simeiz-Katzively co-location site

Abstract : The agreement between local ties of measuring points of the stations in the Simeiz-Katzively co-location site and space geodesy estimates of coordinates of these stations was quantified. There are large discrepancies (up to 120 mm) between these data, the reason for which needs a further study.

Name : ZACHARIAS Norbert

Institut : US Naval Observatory

Co-Authors : N.Zacharias, C.Finch

Type of presentation : ORAL

Country : USA

Title : Deep South Telescope

Abstract : The US Naval Observatory acquired a 1-meter telescope, the Deep South Telescope (DST). It was deployed at Cerro Tololo Interamerican Observatory (CTIO), Chile in March 2019. A 4k CCD camera will be used to image selected optical counterparts of ICRF sources which display significant radio-optical position offsets. This high cadence observing program is part of a joint effort between USNO and Paris Observatory under the FRAMEx program of AGN monitoring. DST will also be used for other programs in the future, including near IR observations with a camera mounted at the 2nd Nasmyth focus.

Name : ZOTOV Leonid

Institut : Lomonosov Moscow State University

Type of presentation : ORAL

Country : RUSSIA

Title : CHANDLER WOBBLE VARIABILITY

Abstract : The works that we carried out during the last ten years lead to significant progress in the knowledge of the Chandler wobble (CW) of the Earth polar motion. In paper [1] we reconstructed the excitation of this resonant mode by using Panteleev corrective filtering. Now we are sure, that this filtering is a regularizing algorithm as far as its parameters are consistently selected with the uncertainty affecting the resonance parameters and the observations. The excitation demonstrated a quasi 20-year amplitude modulation. In the framework of the first order differential linear equation describing the polar motion, it is easy to show that this modulation accounts for the 40-year change of the CW amplitude as well as the splitting of the CW spectra. A simple model of the CW, composed of 80 and 40-year harmonics, accounts for the present minimum in Chandler wobble amplitude, like in 1930s, and also predicts that its amplitude will start to increase in the nearest future with a phase shift of 180 degree. On the other hand, geodetic excitation of the CW well matches the ocean-atmospheric excitation [2,3,4] over recent 50 years with a dominant role of the ocean, producing the 20-year modulation. Thus, the physical cause of it could stem from climatic or tidal process influencing the oceanic circulation. This work is supported by Chinese Discipline Innovative Engineering Plan of Modern Geodesy and Geodynamics (NSFC grant No. B17033).

Name : ZSCHOCKE Sven

Institut : Lohrmann Observatorium, Technische Universität Dresden

Co-Authors : S. Zschocke

Type of presentation : ORAL

Country : GERMANY

Title : On the post-linear metric of a solar system body

Abstract : The Multipolar Post-Minkowskian (MPM) formalism represents an approach for determining the metric density in the exterior of a compact source of matter. The MPM formalism is used in order to derive the post-linear metric tensor of a solar system body of arbitrary shape and inner structure and oscillational motions. These results are a prerequisite for the relativistic theory of light propagation in the solar system aiming at ultra-highly precise astrometric measurements, where the post-linear coefficients of the metric tensor of solar system bodies become relevant.