Very long baseline interferometry

The diameter of a telescope entrance pupil or the distance between two telescopes determine the baseline, which determines the resolution of the interferometer in combination with the detected wavelength. The table compares the resolution of single telescopes and interferometers at optical and radio wavelengths. Note that the resolution of optical interferometers is comparable to that of radio very long baseline interferometry (VLBI). 

Because of the incredible precision of interferometric techniques, this measured velocity is altogether one percent of the earth s circumference velocity derived from the orbital motion. Very-long-baseline interferometry (VLBI)— which is an exhaustively improved Pogany experiment—can detect Ago 10-9 in the earth s rotation. 

It is possible to produce a precise ephemeris for local use by tracking the satellites from a number of so-called fiducial stations, whose positions are known very precisely, at the same time as the measurements are taken at the new stations (Ashkenazi and Ffoulkes-Jones, 1990). These fiducial stations may be Very Long Baseline Interferometry (VLBI) or Satellite Laser Ranging (SLR) sites, which are usually at considerable distances apart (typically 1000 km), or GPS stations especially established for this purpose (eg EUREF, the European Reference Network) (EUREF, 1989). Using these fiducial stations in a... 

Very Long Baseline Interferometry Technique in which astronomical observations are carried out by separate radio telescopes thousands of miles apart, then combined to form a single image. 

A.C.S. Readhead Radio astronomy and very long baseline interferometry. Sci. Am. 246/6, 38 (1982)... 

J.J. Degnan Satellite laser ranging and very long baseline interferometry. In Encyclopedia of Earth Sciences, Vol. 2, ed. by M. Kauffman (Simon and Schuster MacmiUan, New York 1996) p. 935... 

Self-calibration also relies on a priori information about the sky brightness, but it mainly exploits the fact that the number of systematic errors introduced at each antenna (N) is usually much less than the number of sampled coherences ( A ). The errors can be atmospheric in origin, but any source of error that can be considered to affect each antenna separately can also be removed. Thus, self-calibration can also correct for slow frequency drifts in the frequency standard used at each antenna and has thereby allowed true imaging in very-long-baseline interferometry (VLBI), in which the frequency standards are completely independent from antenna to antenna. 

D. Space-Based Very-Long-Baseline Interferometry... 

One of the striking features of interstellar maser emission is the enormous intensity the maser lines have. In the case of water, the brightness temperature for the source W49 reaches about 1015 °K. Furthermore, the line widths of the observed lines are extremely narrow, typically only a few ten of kHz. Both properties, intense and narrow emission lines, are intrinsic indications of maser emission. It has been found that the angular size of all interstellar maser sources is very small, i.e. much smaller than the spatial resolution obtained with large single dish radiotelescopes. From long baseline interferometry, however, an upper limit has been placed on the apparent source size of about 0.002 seconds of arc (for W49 = 0.0003 , Orion = 0.001 ) (Hills et al., 1972), which, for example, at the distance of Orion, 450 pc, makes this particular water vapor source about 1/2 AU in size. This is comparable with the diameter of a red... 

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