ALMA Memo #303 Water Vapour Radiometers for ALMA

The JCMT-CSO single-baseline interferometer was the first to demonstrate phase correction using the 183 GHz line, using equipment built by Martina Wiedner, Richard Hills and colleagues. Only a limited quantity of data were gathered but the results (ALMA memo 252) were encouraging and suggested that even an uncooled system could provide effective phase calibration at submillimetre wavelengths. Single baseline interferometry at JCMT-CSO is no longer a supported mode of operation, so further observations would be difficult though not perhaps impossible to arrange. It is however possible that two SMA antennas can be equipped with 183 GHz systems, using the radiometer currently at CSO plus a clone of it being built in Canada by Christine Wilson and the HIA. It is unclear when this experiment might produce results on Mauna Kea, but access to a large set of data in a variety of atmospheric conditions would certainly be useful in establishing the capabilities of the technique.