Converting 350 μm tipper opacity to precipitable water vapor for extremely dry sites

In this work, it is present a method to convert atmospheric opacity from 350 μm tipper radiometers to precipitable water vapour (PWV). The dynamic range of these tippers is limited and therefore, their use is confined to sites with very low PWV such as the Chilean Altiplano, with altitudes higher than 5000 m. The main scientific drivers behind this procedure are long term climatological studies in the region and water vapour concentration for calibration of radio-astronomical data. The method presented here differs from a previous version in that the ground temperature at the time of the opacity measurement is now included as input to the procedure, as opposed to the use of long-term temperature averages. This new procedure solves the problem of induced false anomalies in the resultant PWV, allowing the results to be used for PWV studies at any timescale, e.g. from hours to decades. In addition, these improvements notably increase the accuracy of the conversion, when the results are compared with other independent measurements taken simultaneously and with the instruments physically co-located.