Status of ESA’s independent Earth Orientation Parameter products

<p>The availability of highly accurate, up-to-date Earth Orientation Parameters is of major importance for all positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for ESA missions and the EU space programs, e.g. Galileo, EGNOS and Copernicus.</p><p>In the frame of its responsibility to provide the Geodetic reference for ESA missions, ESA’s Navigation Support Office at ESOC is already contributing to the realisation of the International Terrestrial Reference Frame (ITRF) and the combined Earth Orientation Parameters provided by the International Earth Rotation Service (IERS). The contribution is realised through individual contributions to international services such as the International GNSS Service (IGS), the International Laser Ranging Services (ILRS), the International DORIS Service (IDS), the International Earth Rotation Service (IERS) and in the future also to the International VLBI Service (IVS).</p><p>For the combination and the long-term predictions of the Earth orientation products ESA is still relying on the International Earth Rotation Service (IERS). Over the past years, ESA repeatedly experienced problems with outdated or missing predictions of the Earth orientation parameters (Bulletin A). Considering the importance of up-to-date Earth orientation parameters, the dependence on a single source outside Europe is considered a risk for European industry, for ESA missions and for EU programmes. For this reason, ESA initiated in 2017 a study with the target to develop independent ESA Earth Orientation parameter products. This study, executed by a consortium led by the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM), is expected to finish in the course of this year.</p><p>In this presentation we will give an overview of ESAs up-to-date reference products and discuss their quality. It will outline the combination approach and discuss the way forward to an fully operational provision of the ESA Earth Orientation Parameter products.</p>

THE ANALYSIS OF THE STABILITY OF PERMANENT GPS STATION VILNIUS (VLNS) / NUOLAT VEIKIANČIOS VILNIAUS (VLNS) GPS STOTIES STABILUMO ANALIZĖ / АНАЛИЗ СТАБИЛЬНОСТИ ПОСТОЯННО ДЕЙСТВУЮЩЕЙ СТАНЦИИ ГПС VILNIUS (VLNS)

Lithuania has been participating in the activities of the EUREF permanent network since 1996, when GPS station VILNIUS started regular continuous tracking of GPS satellites. The GPS station was established with a help of the Onsala Space Observatory (Sweden) and was mounted in the territory of Vilnius international airport (Lithuania). Four character identifier VLNS and DOMES number 10801M001 were assigned to VILNIUS GPS station by the International Earth Rotation Service in 1999. VILNIUS station is operated and maintained by the Institute of Geodesy of Vilnius Technical University. The main task of the permanent VLNS GPS station is to take part in EUREF activities and serve as reference to GPS campaigns in Lithuania. The aim of this paper is to describe the evolution and current status of the technical equipment of VILNIUS station. The paper also presents the analysis of data quality and a few years interval of coordinate determination at VLNS within the EUREF network. Santrauka EUREF nuolat veikiančių stočių tinklo veikloje Lietuva dalyvauja nuo 1996 m., kai GPS VILNIAUS stotis pradėjo reguliarius matavimus iš GPS palydovų. Stotis įsteigta padedant Onsalos kosmoso observatorijai (Švedija). GPS stotis įrengta Vilniaus tarptautinio oro uosto teritorijoje 1999 metais. Tarptautinė žemės sukimositarnyba stočiai suteikė keturių simbolių identifikatorių VLNS ir DOMES numerį 10801M001. GPS VILNIAUS stotį prižiūri ir valdo Vilniaus Gedimino technikos universiteto Geodezijos instituto specialistai. Pagrindinis stoties uždavinys yra dalyvauti EUREF veikloje, ir tai turi būti atraminis geodezinis punktas GPS kampanijoms Lietuvoje. Straipsnio tikslas – aprašyti dabartinę techninės įrangos būklę ir jos tobulinimo eigą. Pateikiama kelerių metų matavimo duomenų kokybės analizė ir nustatytos koordinatės EUREF tinkle. Резюме В проекте сети постоянно действующих станций ГПС EUREF Литва участвует с 1996 г., когда станция VILNIUS стала производить постоянные измерения со спутников ГПС. Станция была основана при помощи Онсольской космической oбсерватории (Швеция). Станция ГПС установлена на территории Вильнюсского международного аэропорта. В 1999 г. Международная служба вращения Земли присвоила станции код VLNS и DOMES номер 10801М001. Станцией управляют специалисты из Геодезического института Вильнюсского технического университета им. Гедиминаса. Главной задачей станции является участие в мероприятиях EUREF, а также быть основным геодезическим пунктом в кампаниях ГПС на территории Литвы. В статье преследовалась цель описать состояние технического оборудования станции и меры по его улучшению. Представлен анализ данных измерений ГПС за несколько лет и определены геодезические координаты в сети EUREF.

SLR Contribution to Investigation of Polar Motion

The Satellite Laser Ranging (SLR) technique has been used to determine Earth Rotation Parameters (ERP) for over twenty years. Most of results contributed to the International Earth Rotation Service (IERS) are based on analysis of observations of Lageos 1 & 2 satellites collected by the global tracking network of about 40 stations. Now five analysis centers submit operational (with 2–15 days delay) solutions and about ten analysis centers contribute yearly final (up to 23 years) ERP series. Some statistics related to SLR observations and analysis are presented and analyzed. Possible problems in SLR observations and analysis and ways of its solution are discussed.

Seth Carlo Chandler Jr.: The Discovery of Variation of Latitude

It took Seth Carlo Chandler Jr. just one year to discover the 14 month and annual components of the variation of latitude (polar motion) that had eluded the most talented astronomers for more than a century. He succeeded where those before him had failed because: he used a global set of observations that had been painstakingly collected by astronomers of many nationalities over more than 150 years; he ignored the common wisdom that unexpected annual variations in astronomical observations were always caused by temperature effects on instruments or atmospheric refraction anomalies; and he was not misled by the theory, which predicted that the Eulerian wobble must have a period of approximately 10 months. Chandler was a true amateur only in the sense that he pursued astronomy out of love, while making his living as an actuary. He began his scientific training at the youthful age of 15 under the tutelage of Benjamin Pierce, perhaps the greatest American mathematician of that time. He then became: a private assistant to Benjamin Apthorp Gould, Jr., an aide to Gould while employed by the US Coast Survey, and Assistant Editor to Gould for the Astronomical Journal. It would be impossible to understand and appreciate Chandler’s achievements without recognizing his relationship with Gould, his brilliant mentor and lifelong colleague — the man he once described as his “Magnus Apollo.”In 1901 Chandler announced that the 14 month motion was not a simple oscillation but was in itself a compound motion consisting of the previously discovered 428 day component, and a much smaller 436 day component, whose reality was “beyond reasonable doubt.” The beating of two such components would result in a rapid change in the phase and amplitude of the Chandler motion at intervals of about 80 years. If Chandler was correct, in about 2010, give or take perhaps five years, we should see the next occurrence of this phenomenon. With the International Earth Rotation Service in operation there should be no difficulty in detecting and quantifying such an event, very nearly one century after Chandler’s death.

Project MERIT and the Formation of the International Earth Rotation Service

Project MERIT was an international programme to Monitor Earth Rotation and Intercompare the Techniques of observation and analysis. It was conceived by a working group that was set up by the International Astronomical Union in 1978 and was carried through with additional support from the International Union of Geodesy and Geophysics. The first objective was to encourage the development of the use of new techniques, such as laser ranging and radio interferometry, for the regular determination of universal time and polar motion. A successful ‘short campaign’ of observations by six techniques was carried out during the period 1980 August to October. Operational and analysis centres were set up for each technique and a coordinating centre was established at the Bureau International de l’Heure (BIH). The results were reported and discussed at the first MERIT Workshop in 1981.The preparations for the ‘main campaign’, which was held from 1983 September 1 to 1984 October 31, and the plans for the activities that were to follow it were reviewed at the second MERIT Workshop in 1983. Important additional features of the campaign included the use of ‘MERIT Standards’ for the reduction and analysis of the data, the use of electronic techniques for the distribution of data, the comparison of the results with the changes in the angular momentum of the atmosphere and special emphasis on the improvement of the terrestrial reference frame. Proposals for a new International Earth Rotation Service were prepared at the third MERIT Workshop in 1986. The MERIT programme was continued from 1984 until the new service formally started on 1988 January 1. Over the decade the accuracy of the Earth-rotation parameters improved considerably.

History of the Bureau International de l’Heure

At the beginning of the 20th century, the development of radio time signals offered the possibility of unifying the measurements of Universal Time (UT). A new service, the Bureau International de l’Heure, hosted by the Paris Observatory, was entrusted with this task. The BIH began its operation in 1912, although its statutes were officially settled only in 1919. This paper recalls the activities of the BIH on time determination and various connected fields: Earth rotation, reference frames, atomic time. With the importance of atomic time and the emergence of new techniques for the measurement of Earth rotation, a new organization was required. It was prepared by the MERIT and COTES programs (1978) and by the bodies of the Metre Convention, with the active participation of the BIH. The BIH was dissolved at the end of 1987, its work being shared between the Bureau International des Poids et Mesures and the new International Earth Rotation Service.

Introduction of JD 3 ON ‘PRECESSION, NUTATION AND ASTRONOMICAL CONSTANTS IN THE DAWN OF THE 21ST CENTURY’.

Due to the adoption of the new International Celestial Reference Frame (ICRF), the Earth’s Ori-entation Parameters (EOP) will be revised and their definitions will need to be re-examined and clarified. This implies that precession/nutation formulation will be also revised in the future. The precession/nutation theories for a non-rigid Earth suffer from a lack of dissipation in the core and from a mismodeling of the ocean and of the atmospheric effects. The scientific community is examining these questions. The IAU community is consequently not yet ready to adopt a new precession/nutation geophysical model but the users may use the International Earth Rotation Service (IERS) empirical series. In order to review those questions and prepare the future research, the Scientific Organizing Committee (SOC: P. Bretagnon, V.A. Brumberg, N. Capitaine, V. Dehant (Chair), T. Fukushima, E. Groten, H. Kinoshitä, B. Kolaczek, D.D. McCarthy, P.K. Seidelmann and P.T. Wallace) has proposed invited talks on the current situation concerning: (1)the formulation of precession/nutation (N. Capitaine, see paper 1),(2)the planetary theories and their relation to precession/nutation (P. Bretagnon, see paper 2),(3)the precession/nutation for a rigid Earth (J. Souchay and H. Kinoshita, see paper 3),(4)the DExxx JPL ephemerides precision and accuracy (E.M. Standish, see paper 4),(5)the observations of the Celestial Ephemeris Pole (CEP) and in particular the pole offset from which precession/nutation corrections can be derived (M. Feissel and A.M. Gontier, see paper 5),

Earth Orientation - The Current and Future Situation

Sub-milliarcsecond astrometry often requires an accurate characterization of the orientation of the Earth in a quasi-inertial reference frame. The International Earth Rotation Service (IERS) standards provide the current state of the art in the transformation between celestial and terrestrial reference systems. Improvements in the determination of Earth orientation parameters which describe this transformation continue to be made. Current and future capabilities are given.