Temperature-regulated 22 GHz water vapor radiometers for CARMA

Y. S. Jerry Shiao, Leslie W. Looney

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


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 efficiency. 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 the WVR 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.

Original languageEnglish (US)
Title of host publicationMillimeter and Submillimeter Detectors and Instrumentation for Astronomy IV
StatePublished - 2008
EventMillimeter and Submillimeter Detectors and Instrumentation for Astronomy IV - Marseille, France
Duration: Jun 26 2008Jun 28 2008

Publication series

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


OtherMillimeter and Submillimeter Detectors and Instrumentation for Astronomy IV


  • Interferometry
  • Radiometer
  • Water vapor

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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