GPS-derived Precipitable Water Vapour in Antarctica and validation with radiosoundings

The capability of the GPS in retrieving the precipitable water vapour (PWV) content at low- and mid-latitudes has been amply investigated by several studies. In Polar Regions, beyond the classical positioning application, the use of GPS observations for sensing the atmosphere is of particular interest due to its easy and unmanned operability. It is well known that, in those areas, the atmospheric water vapour content is approximately one third or less than that present at mid latitudes and that on the Antarctic Plateau the PWV drops down to less than a few mm. As a consequence, the use of GPS data in sensing the atmosphere can be reliably applied only on coastal areas, were the PWV is large enough to exceed the sensitivity of the method. Radio-soundings are periodically performed at several coastal Antarctic stations, where permanent GPS equipments are also installed. The co-location of GPS and radio-soundings allows a validation of the PWV derived from the geodetic data. In this investigation we present the results of the analysis of continuous long time series of GPS data acquired at Mawson (MAW1), Casey (CAS1), Davis (DAV1), McMurdo (MCM4) and Mario Zucchelli (TNB1) stations during twelve years spanning 1999-2010. Particularly, at each site, the PWV is determined with GPS data and the same parameter derived from the analysis of the radio-sounding is used for validation. The GPS analysis is optimized for Antarctic data, using specific atmospheric models (e.g. the Vienna Mapping Function) and particular care in the data screening and elimination. The sites to be analyzed were selected according to the radiosonde equipment: the Vaisala sensors' readings were corrected specifically with ad hoc models.