Evaluation of Shipborne GNSS Precipitable Water Vapor Over Global Oceans From 2014 to 2018

Atmospheric water vapor plays an essential role in climate change and weather forecasting. However, monitoring water vapor with high spatial and temporal resolutions remains a challenge, especially over ocean regions where observations are insufficient. Shipborne global navigation satellite systems (GNSSs) contribute to enriching water vapor measurements over oceans and also can help validate satellite observations. Due to the lack of long-time serial observations, the performance of shipborne GNSS-derived precipitable water vapor (PWV) is inadequately evaluated on the global ocean scale. In this study, an overall assessment of shipborne GNSS PWV over global oceans is performed based on six voyages from 2014 to 2018. In coastal areas, the PWV differences of shipborne GNSS with respect to (w.r.t.) ground-based GNSS and ground-launched radiosonde data are 2.64 and 2.85 mm in the root mean square (rms), respectively. In open oceans, compared to ship-launched radiosonde profiles and satellite measurements, shipborne GNSS PWV shows the rms of differences of 2.54 and 2.53 mm, respectively. In addition, the rms of PWV differences between the whole track of shipborne GNSS PWV and National Centers for Environmental Prediction (NCEP) Climate Forecast System Version 2 (CFSv2) products is 2.96 mm. The intertechnique validations demonstrate that the accuracy of shipborne GNSS PWV is superior to 3 mm, which meets the requirements of climate research and numerical weather prediction (NWP).

Automated summary

In this study, an overall assessment of shipborne GNSS-derived precipitable water vapor (PWV) over global oceans is performed based on six voyages from 2014 to 2018. The results show that shipborne GNSS PWV has a good accuracy, with differences compared to ground-based GNSS, ground-launched radiosonde data, ship-launched radiosonde profiles, and satellite measurements all falling within 3 mm. These findings demonstrate the importance and reliability of shipborne GNSS as a tool for climate research and numerical weather prediction.