Astronomy and Astrophysics Supplement Series, Vol. 119, November I 1996, 559-567
Radiometric monitoring of atmospheric water vapor as it pertains to phase correction in millimeter interferometry
Department of Astronomy, University of Illinois, 1002 W. Green St., Urbana, IL 61801, U.S.A.
Received November 21, 1995; accepted March 26, 1996
Abstract:Water vapor in the Earth's troposphere produces fluctuations in the phase of millimeter-wavelength radiation from astronomical sources. Such fluctuations seriously limit the spatial resolution achievable with current millimeter interferometers. Since water vapor is also a source of atmospheric opacity at these wavelengths, radiometric measurements of sky brightness may be used to monitor the fluctuating water vapor content of the atmosphere and thereby the fluctuations in the interferometric phase. The atmospheric opacity depends on the frequency and on the physical conditions of those atmospheric regions in which the water vapor is located. Atmospheric temperature influences the strengths of the various absorption lines, and pressure influences the degree of line broadening. The magnitude of the phase fluctuations relative to the brightness fluctuations is therefore also dependent on frequency, temperature, and pressure. The frequency of a radiometric monitoring system may be chosen to minimize the dependence of this ratio on the atmospheric parameters.
Key words: atmospheric effects --- instrumentation: interferometers --- methods: observational --- techniques: interferometric