Real-time shipborne multi-GNSS atmospheric water vapor retrieval over the South China Sea

Atmospheric water vapor plays a prominent role in weather forecasting and climate change, which can be measured accurately with conventional water vapor observing techniques and the global navigation satellite system (GNSS). However, there are limited studies that assess the retrieval of PWV exclusively using Beidou over oceans, as well as for GLONASS and Galileo. In this contribution, we investigate retrieving the real-time precipitable water vapor (PWV) based on shipborne GNSS kinematic precise point positioning (PPP) solutions through an 8-days experiment over the South China Sea. Observations from multi-constellation and single-constellation, including GPS, GLONASS, Galileo, and Beidou are processed. Real-time shipborne GNSS PWV is validated using ERA5 PWV products. The results obtained from the single-constellation analysis indicate that Beidou performs comparably to Galileo in PWV retrieval, surpasses GLONASS, but slightly falls behind GPS. It exhibits an accuracy of 3.19 mm when compared to the ERA5 PWV products after an average initialization time of 43.9 min. Furthermore, it is demonstrated that real-time multi-GNSS PWV achieves an accuracy improvement of more than 15% compared to single-constellation resolutions, reaching an accuracy of 2.34 mm. Real-time shipborne GNSS can accurately sense atmospheric water vapor over oceans and contribute to time-critical meteorological applications.