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Proceedings Paper

Temperature-regulated 22 GHz water vapor radiometers for CARMA
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Paper Abstract

The Combined Array for Research in Millimeter-wave Astronomy (CARMA) have carried out a water vapor radiometer (WVR) project to test the WVR phase correction technique for better observational effciency. We have built two uncooled, but temperature-regulated, 22 GHz WVR prototypes to explore the feasibility of the technique. To better isolate the effects of instrumental and atmospheric instabilities, we have optimized theWVR design for simplicity with less high frequency components. The calibration system is Dicke switch with a single ambient load. The thermal regulation system consists of heaters and multi-stage insulation. We have completed testing of the WVR prototypes in a laboratory and at the CARMA site. The gain stability is about 20-100 mK and the front-end temperature rms is about a few mK to hundreds, depending on weather conditions. Based on the site tests, the sky temperature at 22 GHz usually varies a few K in 15 minutes, which is not necessary due to the atmospheric water vapor. Such short time-scale background temperature variation overwhelms the limit of the WVR dynamic range. Moreover, we have compared the WVR data rms with the phase monitor at the site and obtain a scale factor of the 22 GHz water vapor line, 6-12, which is consistent with the results of other WVR projects. We suggest that expanding the WVR dynamic range with diode detector models and a better thermal regulation system are keys to the success of the CARMA WVR phase correction.

Paper Details

Date Published: 18 July 2008
PDF: 12 pages
Proc. SPIE 7020, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV, 70202F (18 July 2008); doi: 10.1117/12.789749
Show Author Affiliations
Y.-S. Jerry Shiao, Univ. of Illinois at Urbana-Champaign (United States)
Leslie W. Looney, Univ. of Illinois at Urbana-Champaign (United States)

Published in SPIE Proceedings Vol. 7020:
Millimeter and Submillimeter Detectors and Instrumentation for Astronomy IV
William D. Duncan; Wayne S. Holland; Stafford Withington; Jonas Zmuidzinas, Editor(s)

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