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Paper: Phase Correction on Mauna Kea Using 183 GHz Water Vapor Monitors
Volume: 217, Imaging at Radio Through Submillimeter Wavelengths
Page: 327
Authors: Wiedner, M. C.; Hills, R. E.
Abstract: Correcting for phase fluctuations caused by atmospheric water vapor is one of the main challenges faced by millimeter and submillimeter interferometry, and routine subarcsecond imaging will only be possible once this problem is solved. For phase correction at the CSO-JCMT submillimeter interferometer we have built two simple uncooled water vapor monitors (wvm) which measure the intensity of the strong 183 GHz water transition. The monitors are mounted on the telescopes so that they probe (nearly) the same atmosphere as the astronomical beam traverses. Since the center of the 183 GHz water vapor line already saturates with 2 mm precipitable water vapor (pwv) we measure the line intensity in three channels in the line wings, 1.2, 4.2 and 7.8 GHz away from the line center. These lines have high, but varying sensitivities of 20 - 3 K per mm of optical path for 0.5 to 4 mm pwv (cf. 0.4 K/mm at 22 GHz, 1.7 K/mm at 220 GHz). For observations at 350 GHz the wvms reduced the rms phase from 60circ (140 microns) to 26 circ (62 microns) (1.5 mm pwv) (, i.e. the amplitude decorrelation is reduced from 42% to 10%), and from random (~350 microns) to 48 circ (110 microns) (3.3 mm pwv) (100% to 30%).
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