Very Long Baseline Interferometry

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Very Long Baseline Interferometer

Author : Fujinobu Takahashi
ISBN : 4274903788
Genre : Radio interferometers
File Size : 33.56 MB
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VLBI is an acronym for Very Long Baseline Inferometry, and can be roughly divided into two areas of application. The first area is in geodesy, which is covered in considerable detail in this book. The second area is in astrometry, or radio astronomy, which is only briefly treated in the book.
Category: Radio interferometers

Very Long Baseline Interferometry

Author : Marcello Felli
ISBN : 9789400924284
Genre : Science
File Size : 65.73 MB
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The quest for high resolution has preoccupied radio astronomers ever since radio waves were first detected from space fifty years ago. This venture was par ticularly stimulated by the discovery of quasars, and led to the development of interferometer techniques using baselines of transglobal dimensions. These meth ods have become known as Very Long Baseline Interferometry (VLBI). Arrays of radio telescopes situated all over the Earth (or even in space) are regularly used for researches in radio astronomy, reaching resolutions as small as a fraction of a milli arcsecond. The technique also allows the measurement of the positions of the radio telescopes to a few millimeters and so VLBI has become a major tool in geodesy and the study of the rotation of the Earth. VLBI has now passed the pioneer stage and is becoming a standard facility available to astronomers and geodesists, requiring the coordination of the operations of indpendently owned radio telescopes around the world. In Europe observatories from England, Federal Republic of Germany, France, Italy, Poland, Sweden and The Netherlands are coordinated in their VLBI activity by the European VLBI Network Consortium (EVN). The Programme Committee of the EVN allocates time to scientific projects on a routine basis three times a year. The Unites States has a similar arrangement of a network of independent radio observatories, and joint experiments using 'Global Network' are often made.
Category: Science

Very Long Baseline Interferometry Applied To Polar Motion Relativity And Geodesy

Author : Chopo Ma
ISBN : OSU:32435031737117
Genre : Aeronautics
File Size : 85.90 MB
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"The causes and effects of diurnal polar motion are described. An algorithm is developed for modeling the effects on very long baseline interferometry observables. Five years of radio-frequency very long baseline interferometry data from stations in Massachusetts, California, and Sweden are analyzed for diurnal polar motion. It is found that the effect is larger than predicted by McClure. Corrections to the standard nutation series caused by the deformability of the earth have a significant effect on the estimated diurnal polar motion scaling factor and the post-fit residual scatter. Simulation3 of high precision very long baseline interferometry experiments taking into account both measurement uncertainty and modeled errors are described. It is found that the Wide-Band Optical Very Long Baseline Interferometer may be useful in studying gravitational deflection near Jupiter. A selection is made between two three-station networks for monitoring polar motion. The effects of scheduling and the number of sources observed on estimated baseline errors are discussed. It is found that a moderate number of sources should yield the best results. A comparison of actual and simulated experiments indicates that the present variability of real data is not well predicted."--Page [i].
Category: Aeronautics

New Calibration Sources For Very Long Baseline Interferometry At 1 6 Ghz

Author : Mekuanint Kifle Hailemariam
ISBN : OCLC:1062356577
Genre : Very long baseline interferometry
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I present new 1.6 GHz VLBI observations of sample of 43 radio sources in the Southern celestial Hemisphere. My goals were firstly to establish the suitability of the 43 sources as calibrators for 1.6 GHz VLBI observations, and secondly to determine, based on some selected sources from the sample, how the properties of the sources seen at 8.4 GHz are related to those seen at 1.6 GHz. I used seven telescopes; ASKAP, ATCA, Ceduna, Hobart, Mopra and Parkes from Australia, and HartRAO from South Africa. By evaluating the sources radial extents, flux density of the central components of the sources and their brightness, I classified the sources into very good, good, intermediate and bad calibrators. Among the 43 sources, I found that 38 sources fell into the good or very good calibrator classes. Among 35 of our sources, which are known to be good calibrators at 8.4 GHz, I found that 32 sources fell into the good or very good calibrator classes. Of the basis of my sample therefore, I can say that 91 percent of the good calibrators at 8.4 GHz are also safe to use at 1.6 GHz.
Category: Very long baseline interferometry

Interferometry And Synthesis In Radio Astronomy

Author : A. Richard Thompson
ISBN : 9783319444314
Genre : Science
File Size : 81.78 MB
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This book is open access under a CC BY-NC 4.0 license. The third edition of this indispensable book in radio interferometry provides extensive updates to the second edition, including results and technical advances from the past decade; discussion of arrays that now span the full range of the radio part of the electromagnetic spectrum observable from the ground, 10 MHz to 1 THz; an analysis of factors that affect array speed; and an expanded discussion of digital signal-processing techniques and of scintillation phenomena and the effects of atmospheric water vapor on image distortion, among many other topics. With its comprehensiveness and detailed exposition of all aspects of the theory and practice of radio interferometry and synthesis imaging, this book has established itself as a standard reference in the field. It begins with an overview of the basic principles of radio astronomy, a short history of the development of radio interferometry, and an elementary discussion of the operation of an interferometer. From this foundation, it delves into the underlying relationships of interferometry, sets forth the coordinate systems and parameters to describe synthesis imaging, and examines configurations of antennas for multielement synthesis arrays. Various aspects of the design and response of receiving systems are discussed, as well as the special requirements of very-long-baseline interferometry (VLBI), image reconstruction, and recent developments in image enhancement techniques and astrometric observations. Also discussed are propagation effects in the media between the source and the observer, and radio interference, factors that limit performance. Related techniques are introduced, including intensity interferometry, optical interferometry, lunar occultations, tracking of satellites in Earth orbit, interferometry for remote Earth sensing, and holographic measurements of antenna surfaces. This book will benefit anyone who is interested in radio interferometry techniques for astronomy, astrometry, geodesy, or electrical engineering.
Category: Science

Interferometry And Synthesis In Radio Astronomy

Author : A. Richard Thompson
ISBN : 9783527617852
Genre : Science
File Size : 40.75 MB
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Comprehensive, authoritative coverage of interferometric techniques for radio astronomy In this Second Edition of Interferometry and Synthesis in Radio Astronomy, three leading figures in the development of large imaging arrays, including very-long-baseline interferometry (VLBI), describe and explain the technology that provides images of the universe with an angular resolution as fine as 1/20,000 of an arcsecond. This comprehensive volume begins with a historical review followed by detailed coverage of the theory of interferometry and synthesis imaging, analysis of interferometer response, geometrical relationships, polarimetry, antennas, and arrays. Discussion of the receiving system continues with analysis of the response to signals and noise, analog design requirements, and digital signal processing. The authors detail special requirements of VLBI including atomic frequency standards, broadband recording systems, and antennas in orbit. Further major topics include: * Calibration of data and synthesis of images * Image enhancement using nonlinear algorithms * Techniques for astrometry and geodesy * Propagation in the neutral atmosphere and ionized media * Radio interference * Related techniques: intensity interferometry, moon occultations, antenna holography, and optical interferometry Interferometry and Synthesis in Radio Astronomy, Second Edition is comprehensive in that it provides an excellent overview of most radio astronomical instrumentation and techniques.
Category: Science

The Role Of Vlbi In Astrophysics Astrometry And Geodesy

Author : Franco Mantovani
ISBN : 9781402024061
Genre : Science
File Size : 59.73 MB
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A masterly survey of the last 13 years of Very Long Baseline Interferometry, reviewed in light of the most advanced astronomical observations. Topics covered include: Nonthermal emission from extragalactic radio sources; Principles of synchrotron emission in relation to astrophysics; Theory of relativistic jets; Young, powerful radio sources and their evolution; Scintillation in extragalactic radio sources; Radio and optical interferometry; Radio polarimetry; Unified schemes; Deep fields; Tropospheric and ionospheric phase calibration; Supernovae; VLBI for geodesy and geodynamics.
Category: Science

Diffraction Limited Imaging With Very Large Telescopes

Author : D.M. Alloin
ISBN : 0792301927
Genre : Science
File Size : 33.21 MB
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A few years ago, a real break-through happened in observational astronomy: the un derstanding of the effect of atmospheric turbulence on the structure of stellar images, and of ways to overcome this dramatic degradation. This opened a route to diffraction-limited observations with large telescopes in the optical domain. Soon, the first applications of this new technique led to some outstanding astrophysical results, both at visible and infrared wavelengths. Yet, the potential of interferometric observations is not fully foreseeable as the first long-baseline arrays of large optical telescopes are being built or cOIIllnissioned right now. In this respect a comparison with the evolution of radio-astronomy is tempting. From a situation where, in spite of the construction of giant antennas, low angular resolution was prevailing, the introduction of long baseline and very long baseline interferometry and the rapid mastering of sophisticated image reconstruction techniques, have brought on a nearly routine basis high dynamic range images with milliarcseconds resolution. This, of course, has completely changed our views of the radio sky.
Category: Science

Literature 1983

Author : S. Böhme
ISBN : 9783662111840
Genre : Science
File Size : 78.95 MB
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Astronomy and Astrophysics Abstracts aims to present a comprehensive documen tation of the literature concerning all aspects of astronomy, astrophysics, and their border fields. It is devoted to the recording, summarizing, and indexing of the relevant publications throughout the world. Astronomy and Astrophysics Abstracts is prepared by a special department of the Astronomisches Rechen-Institut under the auspices of the International Astronomical Union. Volume 33 records literature published in 1983 and received before August 1, 1983. Some older documents which we received late and which are not surveyed in earlier volumes are included too. We acknowledge with thanks contributions of our colleagues all over the world. We also express our gratitude to all organizations, observatories, and publishers which provide us with complimentary copies of their publications. Starting with Volume 33, all the recording, correction, and data processing work was done by means of computers. The recording was done by our technical staff members Ms. Helga Ballmann, Ms. Mona El-Choura, Ms. Monika Kohl, and Ms. Sylvia Matyssek. Mr. Martin Schlotelburg and Mr. Ulrich Uberall supported our task by careful proofreading. It is a pleasure to thank them all for their encouragement. Heidelberg, September 1983 The Editors Contents Introduction . . . . . . . . . . . . 1 Concordance Relation: ICSU-AB-AAA 3 Abbreviations 10 Periodicals, Proceedings, Books, Activities 001 Periodicals . . . . . . . . . . . 15 002 Bibliographical Publications, Documentation, Catalogues, Atlases 47 003 Books ...... . 51 004 History of Astronomy 58 005 Biography . . 64 006 Personal Notes 65 007 Obituaries . . .
Category: Science

An Introduction To Radio Astronomy

Author : Bernard F. Burke
ISBN : 9780521878081
Genre : Science
File Size : 25.40 MB
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This well-established, graduate-level textbook is a thorough introduction to radio telescopes and techniques for students and researchers new to the subject.
Category: Science