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Science 7 January 1983:
Vol. 219. no. 4580, pp. 51 - 54
DOI: 10.1126/science.219.4580.51
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Articles

Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

ALAN E. E. ROGERS 1, ROGER J. CAPPALLO 1, HANS F. HINTEREGGER 1, JAMES I. LEVINE 1, EDWIN F. NESMAN 1, JOHN C. WEBBER 1, ALAN R. WHITNEY 1, THOMAS A. CLARK 2, CHOPO MA 2, JAMES RYAN 2, BRIAN E. COREY 3, CHARLES C. COUNSELMAN 3, TOMAS A. HERRING 3, IRWIN I. SHAPIRO 3, CURTIS A. KNIGHT 4, DAVID B. SHAFFER 4, NANCY R. VANDENBERG 4, RICHARD LACASSE 5, ROBERT MAUZY 5, BENNO RAYHRER 5, BRUCE R. SCHUPLER 6, and J. C. PIGG 6

1 Haystack Observatory, Westford, Massachusetts 01886
2 Goddard Space Flight Center, Greenbelt, Maryland 20771
3 Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge 02139
4 Phoenix Corporation, McLean, Virginia 22102
5 National Radio Astronomy Observatory, Green Bank, West Virginia 24944
6 Computer Science Corporation, Silver Spring, Maryland 20910

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.

Submitted on May 18, 1982


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