Sensing Real-Time Water Vapor Over Oceans With Low-Cost GNSS Receivers

Water vapor over oceans is significant for numerical weather prediction (NWP) and climate research. Ocean platform-based global navigation satellite system (GNSS) which can sense the atmospheric water vapor is becoming an important supplement for water vapor measurements over oceans. However, the application of ocean platform-based GNSS meteorology is normally based on geodetic GNSS receivers, which implies the high cost of hardware. In this contribution, we investigate the potential of retrieving real-time water vapor over oceans with a low-cost receiver (u-blox F9P), and a geodetic GNSS receiver (Trimble NetR9) is also equipped in the experiment vessel. The post-processed Trimble NetR9 zenith total delay (ZTD) estimates and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 precipitable water vapor (PWV) products are used for the validation of real-time ZTDs and PWV values. The results show that the real-time ZTDs derived from the low-cost multi-GNSS (GPS + Galileo) observations obtain a difference of over 2.13 cm in root-mean-square (rms) compared to the post-processed ZTDs with an averaged initialization time of approximately 40 min. In addition, compared to ERA5 PWV, the real-time PWV derived from u-blox F9P multi-GNSS observations shows a difference in rms of approximately 4 mm. Although u-blox F9P multi-GNSS performs relatively worse than Trimble NetR9 multi-GNSS in real-time ZTD/PWV estimates, the accuracy of low-cost GNSS receivers derived water vapor over oceans can still meet the requirements for NWP and nowcasting, which demonstrates promising prospects in supplementing the measurements of water vapor over oceans.