Precipitable water vapour measurement using GNSS data in the Atacama Desert for millimetre and submillimetre astronomical observations

Abstract

Precipitable water vapour (PWV) strongly affects the quality of data obtained from millimetre- and submillimetre-wave astronomical observations, such as those for cosmic microwave background measurements. Some of these observatories have used radiometers to monitor PWV. In this study, PWV was measured from 2021 April to 2022 April using Global Navigation Satellite System (GNSS) instruments in the Atacama Desert, Chile, where several millimetre- and submillimetre-wave telescopes are located. We evaluated the accuracy of these measurements by comparing them to radiometer measurements. We calculated the PWV from GNSS data using CSRS-PPP (Canadian Spatial Reference System Precise Point Positioning), an online software package. When using GNSS data alone, the estimated PWV showed a systematic offset of +1.08 mm. When combining GNSS data with data from a barometer, which was co-located with the GNSS receiver, the estimated PWV showed a lower systematic offset of -0.05 mm. The GNSS PWV showed a statistical uncertainty of 0.52 mm with an averaging time of an hour. Compared to other PWV measurement methods, GNSS instruments are robust in bad weather conditions, have sufficient time resolution, and are less expensive. By demonstrating good accuracy and precision in low-PWV conditions, this paper shows that GNSS instruments are valuable tools for PWV measurements for observing site evaluation and data analysis for ground-based telescopes.