Getting a Clear View Through the Atmosphere - Radiometric Phase Correction at 183 GHz

Details Getting a Clear View Through the Atmosphere - Radiometric Phase Correction at 183 GHz Getting a Clear View Through the Atmosphere - Radiometric Phase Correction at 183 GHz

Oct 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999alma.confe..69w&link_type=abstract

Science with the Atacama Large Millimeter Array (ALMA), Associated Universities, Inc., held October 6-8, 1999 at Carnegie Instit

Astronomy and Astrophysics

Astronomy

Water Vapor, Phase Fluctuation, Angular Resolution, 183 Ghz

Scientific paper

At millimeter wavelengths, phase fluctuations caused by changing amounts of water vapor in the atmosphere disturb the images formed by ground-based instruments, in a manner similar to the effects of "seeing" familiar to optical astronomers. Unless corrections are applied, these fluctuations will render impossible observations of faint objects with an angular resolution of better than a few tenths of an arc second, even on a good site, such as Chajnantor. Our poster will explain the cause of these phase corrections and methods of phase correction. We describe the first water vapor monitors (wvm's) designed to allow phase correction by measuring the atmospheric emission from the 183 GHz water vapor line (Wiedner, 1998). The two radiometers were tested on Mauna Kea, Hawaii, and in fair weather (2.2 mm pwv) phase correction reduced the rms phase fluctuations from 60o (140 mu m) to 25o (60 mu m) over 30 minutes, i.e. 75% of the intensity of the decorrelated signal was retrieved. Though more testing is necessary, this seems a very promising method to reduce phase fluctuations at ALMA. Wiedner, M. C. 1998, Atmospheric Water Vapour and Astronomical Millimetre Interferometry, PhD Thesis, University of Cambridge http://www.mma.nrao.edu/workinggroups/cal_imaging/183GHz.html