Design of an infrared water vapour monitor for measurements of the atmospheric water content in Antarctica

The Infrared Radiometer for Millimetre Astronomy (IRMA) is a 20 mum (15 THz) water vapour monitor. Using a simple infrared detector to measure the emitted flux across a spectral band containing only water vapour rotational transitions it is possible to determine the precipitable water vapour column abundance (PWV) using an atmospheric model. Water vapour is one of the principal sources of opacity at infrared wavelengths, thus measuring diurnal and seasonal trends in PWV plays an important role in observatory site assessment. The Antarctic plateau, with its high altitude, atmospheric stability, and extremely low humidity, represents a unique location for conducting astronomical observations. The site testing role of the IRMA instrument has been refined through remote operation in both Chile and Hawaii, and has now been extended to include Dome C, Antarctica. One IRMA unit will be integrated into the instrument suite of the University of New South Wales' AASTINO site monitoring facility in September 2007. We present here an overview of the IRMA concept and features that enables their use in site testing applications in remote locations of the Chilean desert. In addition, we describe the modifications required for operation in the low temperature environment (-80degC) encountered at Dome C.