Global VLBI Site Map - VLBI observations are sponsored by over 40 organizations located in 17 countries. 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.
[keywords: VLBI, site map](Added: 26-May-1999 Hits: 806)
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International VLBI Service - This site is the communication center for the IVS: the
International VLBI Service for Geodesy and Astrometry.
IVS is an international collaboration of organizations
that support or operate VLBI (very long baseline
interferometry) components. The site has links to IVS Data
Centers that hold VLBI data and products. Products include
Earth orientation ime series, terrestrial reference frame, and
celestial reference frame.
[keywords: VLBI, Earth rotation, radio astronomy,
Earth orientation, geodynamics, interferometry,
reference frames, length of day, space geodesy](Added: 18-Aug-1999 Hits: 799)
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Very Long Baseline Interferometry (VLBI) - On the most basic level, Very Long Baseline Interferometry, or VLBI, is a geodetic technique that determines the positions of observing stations (sites) on the Earth by measuring the time it takes a radio wavefront from a quasar (source) to reach pairs of sites. For each pair, as the wavefront travels from the source at a constant rate in all directions, the front will arrive at each site at a different time, yielding differences in position, or distance, between the sites. As these distances are measured over time for a network of sites, site positions and position changes over time can be measured. Other factors must be applied to model complications in observing -- for example, changes in the atmosphere that slow the wavefront down.
[keywords: VLBI, Very Long Baseline Interferometry](Added: 26-May-1999 Hits: 843)
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VLBI Program Homepage - The VLBI group coordinates the international geodetic
VLBI observing program in close cooperation with the U.S. Naval Observatory's Earth Orientation Department, performs basic research in geodesy to
improve the VLBI technique, analyzes VLBI data from numerous sources to produce exhaustive reports, and sets standards and performs quality
control functions for the geodetic VLBI community.
[keywords: VLBI, Very Long Baseline Interferometry](Added: 12-Jun-1999 Hits: 798)
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![[Spider Link]](http://earthsciencesportal.gsfc.nasa.gov/spider.cgi?URL=http://cddis.gsfc.nasa.gov/images/ivsmap.gif){kind=link}