Since February 2005, an Infrared Radiometer for Millimeter Astronomy (IRMA) has been measuring precipitable
water vapour levels in Chile at the Gemini South site on Cerro Pachon with a second unit added at the Las
Campanas observatories site in August 2005. We have also started data collection with three additional IRMA
units at three locations for the TMT site testing effort. After a number of technical modifications to ensure
reliable operations at much lower sites than IRMA was designed for, 6 months of near continuous pwv data have
been collected at both existing telescope sites and several months of data at TMT candidate locations. These
data are enabling us to compare the sites on diurnal as well as seasonal timescales.
The Infrared Radiometer for Millimetre wavelength Astronomy (IRMA) is a compact, light weight, low cost, low maintainance water vapour monitor, with an accuracy that enables it to be used to correct the phase distortions caused by atmospheric water vapour in millimetre wavelength interferometers. The IRMA III prototype is a major improvement on earlier versions of IRMA, with an emphasis on simplicity and reliability. We present results of tests conducted on the Smithsonian Millimeter Array (SMA) telescope on Mauna Kea in February 2004. The test campaign involved using three IRMA III devices with the SMA to provide phase correction information for improving the quality of the astronomical interferometric data.