Observations of Quasars using Interferometer Baselines up to 3,074 km

Broten, N. W.; Locke, John; Legg, T. H.; McLeish, C. W.; Richards, R. S.; Chisholm, R. M.; Gush, H. P.; Yen, J. L.; Galt, John

doi:10.1038/215038a0

Cited by 25 publications

(11 citation statements)

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“…34°. This agrees with the detailed analysis of the 21-cm interferometric measurements on this source made between Jodrell Bank and Malvern (20,23).…”

Section: B Measurements Using Resolving Powers Betweensupporting

confidence: 77%

Radio Observations of Angular Structure

Palmer¹

1968

Highlights astron.

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Complete information about the angular sizes and structures of discrete radio sources would, in principle, require observations in many position angles and at a large number of resolving powers, of which the highest power must resolve the smallest significant features in the sources. Since some sources are known to have components with differing radio spectra, similar amounts of data would be required at each of several wavelengths. One would then be able to examine statistically the relation between fringe visibility and resolving power at two or three wavelengths, and hence search for structural differences between different types of discrete sources.

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“…34°. This agrees with the detailed analysis of the 21-cm interferometric measurements on this source made between Jodrell Bank and Malvern (20,23).…”

Section: B Measurements Using Resolving Powers Betweensupporting

confidence: 77%

Radio Observations of Angular Structure

Palmer¹

1968

Highlights astron.

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“…Subsequent history can be traced from the first extragalactic interferometric observations by the National Radio Astronomy Observatory (NRAO)-Arecibo group at 0.6 GHz on a 220-km baseline, the MIT-NRAO group (Moran et al, 1967) at 1.7 GHz, on a baseline of 845 km, and the Canadian long baseline interferometry group (Broten et al, 1967) at 0.4 GHz, on a baseline of 3074 km. Early work in geodesy, astrometry, and clock synchronization was done in 1969 (Cohen, 1972;Hinteregger et al, 1972), yielding accuracies in distances of 2-5 meters and in source positions on the order of 1 arc sec.…”

Section: Introductionmentioning

confidence: 99%

Astrometry and geodesy with radio interferometry: experiments, models, results

1998

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Interferometry at radio frequencies between Earth-based receivers separated by intercontinental distances has made significant contributions to astrometry and geophysics during the past three decades. Analyses of such very long baseline interferometric (VLBI) experiments now permit measurements of relative positions of points on the Earth's surface and of angles between celestial objects at levels of better than one cm and one nanoradian, respectively. The relative angular positions of extragalactic radio sources inferred from this technique presently form the best realization of an inertial reference frame. This review summarizes the current status of radio interferometric measurements for astrometric and geodetic applications. It emphasizes the theoretical models that are required to extract results from the VLBI observables at present accuracy levels. An unusually broad cross section of physics contributes to the required modeling. Both special and general relativity need to be considered in properly formulating the geometric part of the propagation delay. While high-altitude atmospheric charged-particle (ionospheric) effects are easily calibrated for measurements employing two well-separated frequencies, the contribution of the neutral atmosphere at lower altitudes is more difficult to remove. In fact, mismodeling of the troposphere remains the dominant error source. Plate tectonic motions of the observing stations need to be taken into account, as well as the nonpointlike intensity distributions of many sources. Numerous small periodic and quasiperiodic tidal effects also make important contributions to space geodetic observables at the centimeter level, and some of these are just beginning to be characterized. Another area of current rapid advances is the specification of the orientation of the Earth's spin axis in inertial space: nutation and precession. Highlights of the achievements of very long baseline interferometry are presented in four areas: reference frames, Earth orientation, atmospheric effects on microwave propagation, and relativity. The order-of-magnitude improvement of accuracy that was achieved during the last decade has provided essential input to geophysical models of the Earth's internal structure. Most aspects of VLBI modeling are also directly applicable to interpretation of other space geodetic measurements, such as active and passive ranging to Earth-orbiting satellites, interplanetary spacecraft, and the Moon. [S0034-6861(98)

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“…Much more sensitive and precise VLBI systems, which used wider bandwidths and atomic frequency standards, were developed by three other groups. In Canada, an analog recording system was developed with a bandwidth of 1 MHz based on television tape recorders (Broten et al 1967). Fringes were obtained at a frequency of 448 MHz on baselines of 183 and 3074 km on several quasars in April 1967.…”

Section: Very-long-baseline Interferometrymentioning

confidence: 99%