Submillimetre Astronomy From The Ground
The most significant limitation to the detection of astronomical emission at submillimetre wavelengths with ground based observatories is atmospheric emission, noise and attenuation. Like the infrared, the submillimetre atmosphere is dominated by numerous water vapour absorption bands and it is only through "windows" between these bands that observations are possible. The ideal submillimetre observing site is dry, cool, has stable weather conditions and is away from urban population centres. There are only a handful of such sites identified, they include Mauna Kea (Hawaii, USA), the Llano de Chajnantor Observatory on the Atacama Plateau (Chile), the South Pole, and Hanle in India (the Himalayan site of the Indian Astronomical Observatory. Comparisons show that all four sites are excellent for submillimetre astronomy, and of these sites Mauna Kea is the most established and arguably the most accessible. There has been some recent interest in high-altitude Arctic sites, particularly Summit Station in Greenland where the PWV measure is always better than at Mauna Kea
The Llano de Chajnantor Observatory site hosts the Atacama Pathfinder Experiment (APEX), the largest submillimetre telescope operating in the southern hemisphere, and the world's largest ground based astronomy project, the Atacama Large Millimeter Array (ALMA), an interferometer for submillimetre wavelength observations made of 54 12-metre and 12 7-metre radio telescopes. The Submillimeter Array (SMA) is another interferometer, located at Mauna Kea, consisting of eight 6-metre diameter radio telescopes. The largest existing submillimetre telescope, the James Clerk Maxwell Telescope, is also located on Mauna Kea.
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