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Proceedings Paper

Atmospheric phase characteristics of the ALMA long baseline
Author(s): Satoki Matsushita; Yoshiharu Asaki; Edward B. Fomalont; Denis Barkats; Stuartt A. Corder; Richard E. Hills; Ryohei Kawabe; Luke T. Maud; Koh-Ichiro Morita; Bojan Nikolic; Remo P. J. Tilanus; Catherine Vlahakis
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Paper Abstract

Atacama Large Millimeter/submillimeter Array (ALMA) is the world’s largest millimeter/ submillimeter (mm / Submm) interferometer. Along with science observations, ALMA has performed several long baseline campaigns in the last 6 years to characterize and optimize its long baseline capabilities. To achieve full long baseline capability of ALMA, it is important to understand the characteristics of atmospheric phase fluctuation at long baselines, since it is believed to be the main cause of mm/submm image degradation. For the first time, we present detailed properties of atmospheric phase fluctuation at mm/submm wavelength from baselines up to 15 km in length. Atmospheric phase fluctuation increases as a function of baseline length with a power-law slope close to 0.6, and many of the data display a shallower slope (02.-03) at baseline length greater than about 15 km. Some of the data, on the other hand, show a single slope up to the maximum baseline length of around 15 km. The phase correction method based on water vapor radiometers (WVRs) works well, especially for cases with precipitable water vapor (PWV) greater than 1 mm, typically yielding a 50% decrease or more in the degree of phase fluctuation. However, signicant amount of atmospheric phase fluctuation still remains after the WVR phase correction: about 200 micron in rms excess path length (rms phase fluctuation in unit of length) even at PWV less than 1 mm. This result suggests the existence of other non-water-vapor sources of phase fluctuation. and emphasizes the need for additional phase correction methods, such as band-to-band and/or fast switching.

Paper Details

Date Published: 27 July 2016
PDF: 13 pages
Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 99064X (27 July 2016); doi: 10.1117/12.2231846
Show Author Affiliations
Satoki Matsushita, Academia Sinica Institute of Astronomy and Astrophysics (Taiwan)
Yoshiharu Asaki, Joint ALMA Observatory (Chile)
National Astronomical Observatory of Japan, Chile Observatory (Chile)
Edward B. Fomalont, Joint ALMA Observatory (Chile)
National Radio Astronomy Observatory (United States)
Denis Barkats, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Stuartt A. Corder, Joint ALMA Observatory (Chile)
National Radio Astronomy Observatory (United States)
Richard E. Hills, Cavendish Lab., Univ. of Cambridge (United Kingdom)
Ryohei Kawabe, National Astronomical Observatory of Japan (Japan)
Univ. of Tokyo (Japan)
SOKENDAI (Japan)
Luke T. Maud, Leiden Observatory (Netherlands)
Koh-Ichiro Morita, Joint ALMA Observatory (Chile)
National Astronomical Observatory of Japan, Chile Observatory (Chile)
Bojan Nikolic, Cavendish Lab., Univ. of Cambridge (United Kingdom)
Remo P. J. Tilanus, Leiden Observatory, Leiden Univ. (Netherlands)
Catherine Vlahakis, Joint ALMA Observatory (Chile)
National Radio Astronomy Observatory (United States)


Published in SPIE Proceedings Vol. 9906:
Ground-based and Airborne Telescopes VI
Helen J. Hall; Roberto Gilmozzi; Heather K. Marshall, Editor(s)

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