Measurements of atmospheric water vapor above Mauna Kea using an infrared radiometer

Astronomical arrays operating at (sub)millimeter wavelengths are seriously compromised by rapid variations in atmospheric water vapor that distort the phase coherence of incoming celestial signals. The signal received by each antenna of the array suffers a phase delay that varies rapidly with time and from antenna to antenna. Unless corrected, these distortions limit the coherence time of the array and seriously compromise its sensitivity and image quality. Building on the success of a prototype infrared radiometer for millimeter astronomy (IRMA), which operates in the 20μm region to measure the column abundance of atmospheric water vapor, this paper presents results obtained with a second generation IRMA operating at the James Clerk Maxwell telescope (JCMT) between January and July 2001. The results are compared with other measures of water vapor available on the summit of Mauna Kea, including: the JCMT SCUBA bolometer camera, the California Institute of Technology (CSO) opacity monitors, the JCMT 183GHz water vapor radiometer and Hilo-launched radiosonde data.