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Topic: VLBI

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Very Long Baseline Interferometry

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	MERLIN : VLBI - Spanning the World.
		VLBI differs from other kinds of interferometry in that the individual telescopes do not need to be connected in anyway.
		VLBI picture of the centre of Virgo A showing a narrow jet issuing from the core.
		VLBI image of the complex jet in 3C48, the second quasar to be discovered.
	www.merlin.ac.uk /about/layman/vlbi.html (629 words)

	Radio astronomy
		VLBI involves using a number of antenna linked together to create a giant antenna which can resolve features with smaller angles.
		VLBI is used mostly for mapping and timing.
		It was launched in February 1997 and is orbiting the Earth in an elliptical orbit to enable VLBI observations on baselines between space and ground telescopes.
	www.ebroadcast.com.au /lookup/encyclopedia/vl/VLBI.html (639 words)

	CDDIS \| VLBI Summary
		VLBI is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar.
		VLBI is unique in its ability to make rapid, accurate measurements of the orientation of the terrestrial reference frame with respect to the celestial reference frame.
		VLBI determines with unequaled accuracy the terrestrial reference frame (antenna locations on the Earth), the celestial reference frame (quasar positions on the sky), and Earth's orientation in space.
	cddis.gsfc.nasa.gov /vlbi_summary.html (437 words)

	Very Long Baseline Interferometry - Wikipedia, the free encyclopedia
		The VLBI technique enables this distance to be much greater than that possible with conventional interferometry, which requires antennas to be physically connected by coaxial cable, waveguide, optical fiber, or other type of transmission line.
		However, since the VLBI technique measures the time differences between the arrival of radio waves at separate antennas, it can also be used "in reverse" to perform earth rotation studies, map movements of tectonic plates very precisely (within millimetres), and perform other types of geodesy.
		In VLBI interferometry, the digitized antenna data are usually recorded at each of the telescopes (in the past this was done on large magnetic tapes, but nowadays it is usually done on large RAID arrays of computer disk drives).
	en.wikipedia.org /wiki/VLBI (1439 words)

	VLBI and Radio Astronomy
		On 25 March 2004, the first-ever successful real-time international transmission and processing of VLBI data was conducted between Haystack's Westford antenna in Massachusetts and the Onsala Space Observatory antenna in Sweden.
		The Haystack Observatory at MIT is one of the pioneers in the field of Very-Long-Baseline Interferometry (VLBI) in radio astronomy.
		VLBI techniques involve using multiple radio telescopes simultaneously in an array to record data, which is then stored on magnetic tape and shipped to a central processing site for analysis.
	science.internet2.edu /vlbi.html (1677 words)

	Binary Research Institute (Site not responding. Last check: 2007-10-20)
		VLBI (Very Long Baseline Interferometry), the process of using extragalactic radio sources, such as quasars, to pinpoint changes in the Earth's orientation to inertial space is a tremendously helpful tool.
		As precise as VLBI is in recording and documenting the Earths orientation to space it does not determine the "causes" for the change in orientation.
		The fact of the matter is, unless we had radio telescopes on the surface of the Sun, that could simultaneously coordinate with such devices on the surface of the Earth, we cannot be sure that all the causes of the Earth's changing orientation to inertial space are strictly local.
	www.binaryresearchinstitute.org /evidence/vlbi.shtml (588 words)

	VLBI Astrometry (Site not responding. Last check: 2007-10-20)
		Astrometry is a branch of astronomy that deals with the positions of stars and other celestial bodies, their distances and movements.
		Very Long Baseline Interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy, in which the data received at each antenna in the array is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk.
		The resolution achievable using interferometry is proportional to the distance between the antennas furthest apart in the array.
	www.vlbi-astrometry.org /index.shtml (161 words)

	The Lab for Terrestrial Physics
		VLBI, or Very Long Baseline Interferometry is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar.
		VLBI makes a direct measurement of the Earth's orientation in space from which geoscientists then model such phenomena as atmospheric angular momentum, ocean tides and currents, and the elastic response of the solid Earth.
		VLBI determines with unequaled accuracy the terrestrial reference frame (antenna locations on the Earth), the celestial reference frame (quasar positions on the sky), and Earth's orientation in space.
	ltpwww.gsfc.nasa.gov /ltp/vlbi.html (390 words)

	IERS VLBI Coordinating Centre (Site not responding. Last check: 2007-10-20)
		VLBI measures the time differences in the arrival of microwave signals from extragalactic radio sources received at two or more radio observatories.
		VLBI is the only technique capable of measuring all components of the Earth's orientation accurately and simultaneously.
		Currently, VLBI determinations of earth-rotation variations, and of the coordinates of terrestrial sites and celestial objects are made routinely and regularly with estimated accuracies of about +/-0.2 milliarcsecond or better.
	hpiers.obspm.fr /eop-pc/techniques/VLBI.html (180 words)

	Kozmikus Geodéziai Obszervatórium
		VLBI has important geodetic and geophysical applications as well, such as the determination of Earth rotation and crustal movements.
		VLBI measures the time difference between the arrival of the radio waves at different antennas on the Earth surface.
		We are involved in both VLBI imaging of extremely distant quasars and studies of the apparent angular size-redshift relation for constraining cosmological world models.
	www.sgo.fomi.hu /53-vlbi_eng.html (1678 words)

	Mark-5 VLBI Analysis Software Calc/Solve
		Mark-5 VLBI Analysis Software Calc/Solve is a set of programs for analyzing very long baseline interferometry observations made under astrometric and geodetic programs.
		VLBI analysis system archives the output of correlator post-processing software into the databases, computes theoreticals values of delay and delay/rate, finds adjustments to the parameters of the model by LSQ fit, calculates statistics of the solution, generates tables and plots of the final results and and make a lot of other things.
		User's manual to program snranal for computation the mean correlated flux of each source achieved at the particular geodetic VLBI experiment, for computation of the mean system equivalent flux density (SEFD) of each antenna participated.
	gemini.gsfc.nasa.gov /solve (1636 words)

	Canadian Spatial Reference System - VLBI - Polar Motion
		Forces within the earth, its atmosphere and oceans along with the gravitational pull of the sun and moon act to influence the earths rotation.
		VLBI's precise measurements allow us to very accurately calculate the rotational speed of the earth and observe its changes.
		If we were to use VLBI observations to repeatedly measure the distance between 2 radio telescope located on different continents we could determine speed and direction in which they were moving relative to one another.
	www.geod.nrcan.gc.ca /geodesy/vlbi/vlbi04_e.php (196 words)

	MIT Haystack Observatory: Astronomy Wideband VLBI
		The technique of very long baseline interferometry (VLBI) depends on faithfully recording the fluctuations of electric field caused by incoming radio waves from astronomical sources, as captured by the receiving system of an antenna.
		Already, with recording rates of 1 Gbit/sec through the Mark 5 system, experiments combining the collecting area of the world's largest radio telescopes are achieving greater sensitivity than any in the history of radio astronomy, and further improvements will quickly follow.
		VLBI is in a transition from being an expensive but powerful technique with limited sensitivity, to being an inexpensive and yet more powerful technique, with sensitivity limited only by the constituent antennas of the array.
	www.haystack.edu /ast/uvlbi/index.html (369 words)

	What is... (Site not responding. Last check: 2007-10-20)
		VLBI (Very Long Baseline Interferometry) is one of the most accurate methods used to measure the Earth and its orientation in space.
		With VLBI observations we can determine with great precision irregularities in the rotation of the earth and variations in the direction of the Earth's axis.
		The continuous measurement of the variations of the Earth's rotational speed and orientation of its axis are of great importance for the evolution of our climate, because up to 90% of the effects can be traced back to the influence of the global atmospheric circulation and the tidal currents of the oceans.
	vlbi.geod.uni-bonn.de /English/what_is_english.html (426 words)

	European VLBI Network: Newsletter 17 - May 2007
		EVN, a VLBI network of radio telescopes spread throughout Europe and beyond, operated by an international Consortium of institutes.
		Possibly, the next VLBI symposium in 2008, will be the 1st International VLBI Symposium as a results of a major integration process between the EVN and the VLBA, which started at the EVN CBD meeting held in Bonn.
		The core (to the West) is unpolarised (< 1%) and the jet (to the East) is smoothly polarised with a polarised fraction of approximately 16%.
	www.ira.inaf.it /evnnews (2636 words)

	VLBI and Radio Astronomy
		On 25 March 2004, the first-ever successful real-time international transmission and processing of VLBI data was conducted between Haystack's Westford antenna in Massachusetts and the Onsala Space Observatory antenna in Sweden.
		The Haystack Observatory at MIT is one of the pioneers in the field of Very-Long-Baseline Interferometry (VLBI) in radio astronomy.
		VLBI techniques involve using multiple radio telescopes simultaneously in an array to record data, which is then stored on magnetic tape and shipped to a central processing site for analysis.
	www.internet2.edu /science/vlbi.html (1701 words)

	End of VLBI Data Analysis at NOAA (Site not responding. Last check: 2007-10-20)
		Routine processing of VLBI data and the electronic distribution of Earth orientation results ended on 31 December 1994.
		All operational activities associated with coordinating and scheduling the NEOS and the IRIS Intensive VLBI observing sessions became the sole responsibility of USNO as of 01 January 1995.
		We recognize the vital function that VLBI fulfills in reinforcing the terrestrial reference frame, establishing a stable inertial celestial reference frame, and in determining regular, reliable Earth orientation parameter values, especially UT1.
	www.ngs.noaa.gov /GRD/VLBI/VLBI-END.html (387 words)

	Astronomers Demonstrate a Global Internet Telescope
		VLBI (or Very Long Baseline Interferometry) is a technique used by radio astronomers to image the sky in supreme detail.
		In the past, the VLBI technique was severely hampered because the data had to be recorded onto tape and then shipped to a central processing facility for analysis.
		The data were then delivered to the Joint Institute for VLBI in Europe (JIVE), the central processing facility for the EVN in the Netherlands.
	www.jb.man.ac.uk /news/evlbi (1318 words)

	Metsähovi Radio Observatory: VLBI
		The VLBI observing frequencies of Metsähovi are 22 GHz, 43 GHz and 85 - 115 GHz.
		In 2001 and 2002 "normal" VLBI measurements were slightly disturbed by the antenna system upgrade and the 147 GHz (2 mm) VLBI test experiment.
		By using VLBI space telescope, the resolving power at given wavelength improves as the maximal distance between telescopes increases.
	kurp.hut.fi /vlbi (908 words)

	Astronomical VLBI at HartRAO
		VLBI operations run on the linux-based New Control Computer System at the observatory.
		HartRAO has been involved in a number of VLBI experiments to look at the details of the structure of the jet, and changes in the structure over time.
		In this VLBI image we see fine details of the upper jet as it leaves the area around the fl hole, which is in the centre of the image.
	www.hartrao.ac.za /vlbi (688 words)

	VLBI Instrumentation Basics
		VLBI observatories are usually large, expensive, and not very portable (go to the NASA observatory in Robledo de Chavela, Madrid, and check this for yourself!).
		VLBI instrumentation can be divided into several subsystems including antennas, receivers, frequency standards, calibration, recorders, and correlation.
		Hydrogen masers are the usual VLBI frequency standards, which can be two or more orders of magnitude more stable than rubidium and cesium standards.
	www.ira.cnr.it /~torres/thesis/node9.html (1095 words)

	VLBI at Arecibo Observatory
		The 305-m Arecibo radio telescope became part of the VLBI network in late 1990s as part of the HALCA mission of the Japanese VSOP project.
		The EVN Calculator could be used to estimate the sensitivity of a VLBI observation.
		Currently, all VLBI observations carried out in Arecibo are recorded on Mark 5A disk units.
	www2.naic.edu /~astro/aovlbi (919 words)

	CDDIS \| VLBI Summary
		VLBI is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar.
		VLBI is unique in its ability to make rapid, accurate measurements of the orientation of the terrestrial reference frame with respect to the celestial reference frame.
		The International VLBI Service for Geodesy and Astrometry (IVS) is an international collaboration of organizations which operate or support Very Long Baseline Interferometry (VLBI) components.
	cddisa.gsfc.nasa.gov /vlbi_summary.html (437 words)

	ESA - Space Science - Observations: Very Long Baseline Interferometry (VLBI)
		The Very Long Baseline Interferometry (VLBI) technique – the ultimate case of interferometry – was originally developed in the 1960s by astronomers who were seeking ways to push the angular resolution of radio telescopes to the limits for studies of distant celestial objects.
		In the case of Huygens VLBI tracking, data from about twenty radio telescopes located in Asia, Australia and the United States will be processed at the European VLBI Network Data Processor at JIVE.
		VLBI tracking of Huygens during its parachute descent in the atmosphere of Titan will allow observers to reach an unprecedented accuracy of about one kilometre in determination of the probe’s position - at the distance between Earth and Titan of 1200 million kilometres!
	www.esa.int /esaSC/SEM8FUXDE2E_index_0.html (401 words)

	A VLBI survey at 2.29 GHz
		The VLBI survey is also useful for studying the characteristics of compact radio sources.
		The sample observed with VLBI covers the full sky and was chosen largely on the basis of criteria placed on total 2.7GHz flux density and spectral index alpha between 5 and 2.7GHz, neglecting temporal variability.
		Based on these sample criteria, the VLBI survey is estimated to be 93 % complete, again neglecting temporal variability, with a total of 312 sources observed.
	cats.sao.ru /doc/VLBI_sur.html (1485 words)

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