Remotely operated infrared radiometer for the measurement of atmospheric water vapor

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 20mum region to measure the column abundance of atmospheric water vapor, this paper describes the latest version of the IRMA concept, which has been developed for operation at Llano de Chajnantor, future site of the Atacama Large Millimeter Array (ALMA). Since there is presently limited infrastructure at the Chilean site the design must pay careful attention to all aspects of remote operation.