Atmospheric phase characteristics of the ALMA long baseline

Satoki Matsushita, Yoshiharu Asakik, Edward B. Fomalont, Denis Barkats, Stuartt A. Corder, Richard E. Hills, Rvohei Kawabe, Luke I. Maud, Koh Ichiro Morita, Bojan Nikolic, Remo P. Tilanus, Catherine Vlahakis

Research output: Chapter in Book/Report/Conference proceedingConference contribution

4 Scopus citations


Atacama Large Millimeter/submillimeter Arraj (ALMA) is the world's largest millimeter / submilliineter (mm / submm) interferometer. Along with science observations, ALMA has performed several long baseline campaigns in the last ft years to characterize and optimize its long baseline capabilities, lo 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 miii/siibiiiui image degradation. For the first time, we present detailed properties of atmospheric phase fluctuation at miii/subiiiiii 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 (0.2 - 0.3) at baseline length greater than about 1 km. Some of the data, on the other hand, show a single slope up to the maximum baseline length of around 15 km. l he phase correction method based on water vapor radiometers (WV Rs) works well, especially for cases with preci pi table water vapor (PWV) greater than 1 mm. typicalh yielding a 50% decrease or more in the degree of phase fluctuation. However, significant amount of atmospheric phase fluctuation still remains after the WVH phase correction; about 200 micron in rnis excess path length (rms phase fluctuation iu unit of length) even at PWV less than 1 nun. 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.

Original languageEnglish (US)
Title of host publicationGround-Based and Airborne Telescopes VI
EditorsHeather K. Marshall, Helen J. Hall, Roberto Gilmozzi
ISBN (Electronic)9781510601918
StatePublished - 2016
Externally publishedYes
EventGround-Based and Airborne Telescopes VI - Edinburgh, United Kingdom
Duration: Jun 26 2016Jul 1 2016

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherGround-Based and Airborne Telescopes VI
Country/TerritoryUnited Kingdom


  • ALMA
  • Atmospheric phase fluctuation
  • Long baseline
  • Phase correction

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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