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Paper: Why Single-Dish?
Volume: 278, NAIC-NRAO School on Single-dish Radio Astronomy: Techniques and Applications
Page: 27
Authors: Emerson, Darrel
Abstract: Single-dish radio telescopes and interferometers/aperture synthesis telescopes are complementary. For some tasks - such as obtaining an accurate measurement of large-scale structure in a region of the sky - the single-dish may be the only option. For other tasks, for example where higher resolution is required, then an interferometer may be the only choice. For some tasks - such as where the critical parameter may be total collecting area, no matter how it is configured - then either single-dish or interferometric instruments may be suitable. The fundamental difference between single-dish and interferometric instruments is in the range of angular scale sizes to which they are sensitive. However, purely practical points, such as the relative complexity of interferometer instrumentation with inevitably lower flexibility and the relative difficulty in upgrading instrumentation, and in many cases a steeper learning curve for user software, sometimes make a single-dish the ``telescope of choice'' for a given experiment. On the other hand, the difficulty in obtaining sufficient amplitude stability in single-dish instrumentation sometimes makes an interferometric instrument, which relies on cross-correlation of the signal rather than auto-correlation, a better choice. For a future generation of telescopes, in particular in the mm-wave and submm-wave region, perhaps most observing plans will require a combination of single-dish and interferometric data. Design of the ALMA telescope is nearly complete; this will consist of about 64 individual 12-meter antennas, operating from ~30 GHz up to ~950 GHz. The current design specifies that all 64 antennas will sometimes be operated as independent single-dish instruments, observing the same or different sources. This is in addition to the interferometric mode where all 64 antennas operate together as a multi-element interferometer. With a future generation of radio telescopes, the distinction between purely single-dish instruments and purely interferometer telescopes may become blurred.
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