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Dirk Behrend - One of the best experts on this subject based on the ideXlab platform.
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vlbi a fascinating technique for Geodesy and astrometry
Journal of Geodynamics, 2012Co-Authors: H Schuh, Dirk BehrendAbstract:Abstract Since the 1970s Very Long Baseline Interferometry (VLBI) has proven to be a primary space-geodetic technique by determining precise coordinates on the Earth, by monitoring the variable Earth rotation and orientation with highest precision, and by deriving many other parameters of the Earth system. VLBI provides an important linkage to astronomy through, for instance, the determination of very precise coordinates of extragalactic radio sources. Additionally, it contributes to determining parameters of relativistic and cosmological models. After a short review of the history of geodetic VLBI and a summary of recent results, this paper describes future perspectives of this fascinating technique. The International VLBI Service for Geodesy and Astrometry (IVS), as a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU), is well on its way to fully defining a next generation VLBI system, called VLBI2010. The goals of the new system are to achieve on scales up to the size of the Earth an accuracy of 1 mm in position and of 0.1 mm/year in velocity. Continuous observations shall be carried out 24 h per day 7 days per week in the future with initial results to be delivered within 24 h after taking the data. Special sessions, e.g. for monitoring the Earth rotation parameters, will provide the results in near real-time. These goals require a completely new technical and conceptual design of VLBI measurements. Based on extensive simulation studies, strategies have been developed by the IVS to significantly improve its product accuracy through the use of a network of small (∼12 m) fast-slewing antennas. A new method for generating high precision delay measurements as well as improved methods for handling biases related to radio source structure, system electronics, and deformations of the antenna structures has been developed. Furthermore, as of January 2012, the construction of ten new VLBI2010 sites has been funded, with good prospects for one dozen more antennas, which will improve the geographical distribution of geodetic VLBI sites on Earth and provide an important step toward a global VLBI2010 network. Within this paper, the Global Geodetic Observing System (GGOS) of the IAG will also be introduced and the contribution of VLBI to GGOS will be described.
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the international vlbi service for Geodesy and astrometry ivs current capabilities and future prospects
Journal of Geodesy, 2007Co-Authors: Wolfgang Schluter, Dirk BehrendAbstract:Very Long Baseline Interferometry (VLBI) plays a unique and fundamental role in the maintenance of the global (terrestrial and celestial) reference frames, which are required for precise positioning in many research areas such as the understanding and monitoring of global changes, and for space missions. The International VLBI Service for Geodesy and Astrometry (IVS) coordinates the global VLBI components and resources on an international basis. The service is tasked by the International Association of Geodesy (IAG) and International Astronomical Union (IAU) to provide products for the realization of the Celestial Reference Frame (CRF) through the positions of quasars, to deliver products for the maintenance of the terrestrial reference frame (TRF), such as station positions and their changes with time, and to generate products describing the rotation and orientation of the Earth. In particular, VLBI uniquely provides direct observations of nutation parameters and of the time difference UT1-UTC. This paper summarizes the evolution and current status of the IVS. It points out the activities to improve further on the product quality to meet future service requirements.
W Torge - One of the best experts on this subject based on the ideXlab platform.
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from a regional project to an international organization the baeyer helmert era of the international association of Geodesy 1862 1916
2015Co-Authors: W TorgeAbstract:The following paper describes the first epoch of organized international collaboration in Geodesy, which started about 150 years ago and finally led to today’s “International Association of Geodesy”. This development may be regarded as a consequence of the refined definition of the figure of the Earth, originating at the end of the seventeenth century and leading from the rotational ellipsoid to the equipotential surfaces of the gravity field, close to mean sea level. An increasing number of geodetic enterprises based on astronomic, geodetic and gravimetric measurements followed until the middle of the nineteenth century, in order to determine the curvature of the Earth’s figure at different regions of the world. The arc measurement based on triangulation played a special role at these endeavours, because this method was now increasingly used as the basis for national mapping. In 1861, the retired Prussian General Johann Jacob Baeyer took up earlier ideas from Schumacher, Gauss, Bessel, Struve and others, and proposed an arc measurement project for central Europe in order to systematically study the figure of the Earth in this region. The proposed network ranged from southern Italy to Norway, and from France to Poland, and its survey and evaluation naturally required international cooperation. Baeyer’s initiative immediately got the support from the Prussian government, and the enthusiastic collaboration of the European countries soon reached far beyond the original project. Consequently, the name of this “governmental” scientific organization changed from “Mitteleuropaische Gradmessung” to “Europaische Gradmessung”, and the scientific program widened significantly by including levelling, mean sea level investigations, standardization of length and time measures, and gravity observations. Baeyer remained the dominating person of the “European Arc Measurement” until his death (1885), keeping a strong position as the President of the Association’s Central Bureau hosted at the newly established Prussian Geodetic Institute. The following epoch is governed by Friedrich Robert Helmert, well-known by a fundamental monograph on “Higher Geodesy”, who became appointed Director of the Geodetic Institute and the Central Bureau in 1886. The regional organization immediately extended to the global “Internationale Erdmessung” (“Association Geodesique Internationale”), and the scientific program was enlarged significantly, with strong accent on physical Geodesy and geophysics including investigations on temporal variations. This epoch ended due to the First World War, when the governmental convention on the Association was not extended. Although a reduced association among neutral nations succeeded in keeping the Latitude Service alive, the next era of international cooperation in Geodesy only followed in 1922, within the frame of the non-governmental “International Union of Geodesy and Geophysics”.
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the international association of Geodesy 1862 to 1922 from a regional project to an international organization
Journal of Geodesy, 2005Co-Authors: W TorgeAbstract:Geodesy, by definition, requires international collaboration on a global scale. An organized cooperation started in 1862, and has become today’s International Association of Geodesy (IAG). The roots of modern Geodesy in the 18th century, with arc measurements in several parts of the world, and national geodetic surveys in France and Great Britain, are explained. The manifold local enterprises in central Europe, which happened in the first half of the 19th century, are described in some detail as they prepare the foundation for the following regional project. Simultaneously, Gauss, Bessel and others developed a more sophisticated definition of the Earth’s figure, which includes the effect of the gravity field. In 1861, the retired Prussian general J.J. Baeyer took up earlier ideas from Schumacher, Gauss, Struve and others, to propose a Central European Arc Measurement in order to study the figure of the Earth in that region. This led to a scientific organization, which soon extended from Central Europe to the whole continent and later to the globe, and changed its name in 1886 to ‘Internationale Erdmessung’ (International Geodetic Association). The scientific programme also widened remarkably from more local studies based on geometric data to regional and global investigations, with gravity measurements as an important source of information. The Central Bureau of the Internationale Erdmessung was hosted at the Prussian Geodetic Institute in Potsdam, and with Baeyer as Director, developed as an efficient tool of the Association. The scientific research extended and deepened after 1886, when F.R. Helmert became Director of the Central Bureau. A stronger international participation then took place, while the influence of the German states reduced. Of great practical importance were questions of standardization and reference systems, but first attempts to interpret gravity field variations and to monitor geodynamic phenomena by geodetic methods indicated future tendencies. With the First World War and the expiry of the last international convention in 1916, the international cooperation within the frame of the Association practically came to an end, which ended the first epoch of the Association. Nevertheless, due to the strong commitment of two scientists from neutral countries, the International Latitude Service continued to observe polar motion and to deliver the data to the Berlin Central Bureau for evaluation. After the First World War, Geodesy became one of the founding members of the International Union for Geodesy and Geophysics (IUGG), and formed one of its Sections (respectively Associations). It has been officially named the International Association of Geodesy (IAG) since 1932.
Antoine Rolland - One of the best experts on this subject based on the ideXlab platform.
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Geodesy and metrology with a transportable optical clock
Nature Physics, 2018Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of Units. However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy, a major challenge remains: their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations. Here, we report the first field measurement campaign with a transportable 87Sr optical lattice clock. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km away, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a 171Yb lattice clock also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.
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Geodesy and metrology with a transportable optical clock
Nature Physics, 2018Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:Optical atomic clocks, due to their unprecedented stability1–3 and uncertainty3–6, are already being used to test physical theories7,8 and herald a revision of the International System of Units9,10. However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy 11 , a major challenge remains: their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations12–14. Here, we report the first field measurement campaign with a transportable 87Sr optical lattice clock 12 . We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km away, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a 171Yb lattice clock 15 also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks. An atomic clock has been deployed on a field measurement campaign to determine the height of a mountain location 1,000 m above sea level, returning a value that is in good agreement with state-of-the-art Geodesy.
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Geodesy and metrology with a transportable optical clock
arXiv: Atomic Physics, 2017Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:The advent of novel measurement instrumentation can lead to paradigm shifts in scientific research. Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of units (SI). However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy, a major challenge remains. This is their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations. Here we report the first field measurement campaign performed with a ubiquitously applicable $^{87}$Sr optical lattice clock. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km apart, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a $^{171}$Yb lattice clock also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.
Christian Lisdat - One of the best experts on this subject based on the ideXlab platform.
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Geodesy and metrology with a transportable optical clock
Nature Physics, 2018Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of Units. However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy, a major challenge remains: their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations. Here, we report the first field measurement campaign with a transportable 87Sr optical lattice clock. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km away, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a 171Yb lattice clock also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.
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Geodesy and metrology with a transportable optical clock
Nature Physics, 2018Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:Optical atomic clocks, due to their unprecedented stability1–3 and uncertainty3–6, are already being used to test physical theories7,8 and herald a revision of the International System of Units9,10. However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy 11 , a major challenge remains: their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations12–14. Here, we report the first field measurement campaign with a transportable 87Sr optical lattice clock 12 . We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km away, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a 171Yb lattice clock 15 also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks. An atomic clock has been deployed on a field measurement campaign to determine the height of a mountain location 1,000 m above sea level, returning a value that is in good agreement with state-of-the-art Geodesy.
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Geodesy and metrology with a transportable optical clock
arXiv: Atomic Physics, 2017Co-Authors: Jacopo Grotti, Silvio Koller, Stefan Vogt, Sebastian Hafner, U Sterr, Christian Lisdat, Heiner Denker, Christian Voigt, Ludger Timmen, Antoine RollandAbstract:The advent of novel measurement instrumentation can lead to paradigm shifts in scientific research. Optical atomic clocks, due to their unprecedented stability and uncertainty, are already being used to test physical theories and herald a revision of the International System of units (SI). However, to unlock their potential for cross-disciplinary applications such as relativistic Geodesy, a major challenge remains. This is their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations. Here we report the first field measurement campaign performed with a ubiquitously applicable $^{87}$Sr optical lattice clock. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km apart, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a $^{171}$Yb lattice clock also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.
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a clock network for Geodesy and fundamental science
Nature Communications, 2016Co-Authors: Christian Lisdat, G Grosche, Nicolas Quintin, C Shi, S M F Raupach, Christian Grebing, D Nicolodi, Fabio Stefani, A AlmasoudiAbstract:Leveraging the unrivalled performance of optical clocks as key tools for geo-science, for astronomy and for fundamental physics beyond the standard model requires comparing the frequency of distant optical clocks faithfully. Here, we report on the comparison and agreement of two strontium optical clocks at an uncertainty of 5 × 10−17 via a newly established phase-coherent frequency link connecting Paris and Braunschweig using 1,415 km of telecom fibre. The remote comparison is limited only by the instability and uncertainty of the strontium lattice clocks themselves, with negligible contributions from the optical frequency transfer. A fractional precision of 3 × 10−17 is reached after only 1,000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than any previous long-distance clock comparison. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second. Comparing the frequency of two distant optical clocks will enable sensitive tests of fundamental physics. Here, the authors compare two strontium optical-lattice clocks 690 kilometres apart to a degree of accuracy that is limited only by the uncertainty of the individual clocks themselves.
Wolfgang Schluter - One of the best experts on this subject based on the ideXlab platform.
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the international vlbi service for Geodesy and astrometry ivs current capabilities and future prospects
Journal of Geodesy, 2007Co-Authors: Wolfgang Schluter, Dirk BehrendAbstract:Very Long Baseline Interferometry (VLBI) plays a unique and fundamental role in the maintenance of the global (terrestrial and celestial) reference frames, which are required for precise positioning in many research areas such as the understanding and monitoring of global changes, and for space missions. The International VLBI Service for Geodesy and Astrometry (IVS) coordinates the global VLBI components and resources on an international basis. The service is tasked by the International Association of Geodesy (IAG) and International Astronomical Union (IAU) to provide products for the realization of the Celestial Reference Frame (CRF) through the positions of quasars, to deliver products for the maintenance of the terrestrial reference frame (TRF), such as station positions and their changes with time, and to generate products describing the rotation and orientation of the Earth. In particular, VLBI uniquely provides direct observations of nutation parameters and of the time difference UT1-UTC. This paper summarizes the evolution and current status of the IVS. It points out the activities to improve further on the product quality to meet future service requirements.
