Retrieval of the precipitable water vapor from shipborne multi-GNSS measurements in tropical cyclone-prone regions of the Northwest Pacific during the summer season in 2021

Abstract. Global Navigation Satellite System (GNSS) is useful for monitoring atmospheric precipitable water vapor (PWV) content. GNSS observations performed in the ocean are relatively rare, making PWV observations at sea difficult to achieve. We previously retrieved shipborne GNSS PWV in the Northwest Pacific and conducted a comparative study with other observation systems. In this study, we demonstrate that reliable results can be obtained for the shipborne GNSS PWV over the ocean by using observations from similar regions at different times and comparing them with another dataset. To achieve this, we introduce the retrieval and validation of PWV from shipborne GNSS observations conducted aboard the research vessel from July 30 to August 25, 2021, in tropical cyclone-prone regions of the Northwest Pacific Ocean. The shipborne GNSS-derived PWV is validated against three reference datasets - radiosonde, low Earth orbit satellite (MetOp-IASI), and geostationary satellite (GK2A-AMI) - to assess its accuracy and reliability in oceanic environments. The GNSS PWV exhibits good agreement with radiosonde measurements, with a mean bias of −0.94 mm and a root mean square (RMS) of 4.28 mm. In addition, the two variables exhibit a correlation coefficient of 0.80. A comparison between GNSS-derived PWV and PWV obtained from GK2A-AMI observations reveals a minimal mean bias of 0.08 mm, which indicates good agreement. The RMS value between the two datasets is slightly greater than that observed with the radiosonde, reaching 4.83 mm. This comparison yields a correlation coefficient of 0.79. Furthermore, the PWV derived from MetOp-IASI shows a substantial bias of 2.58 mm and a relatively large RMS error of 6.99 mm compared with the GNSS PWV, with a correlation coefficient of 0.71. These results are consistent with previous findings. We suggest that the PWV derived from shipborne GNSS observations in tropical cyclone-prone regions of the Northwest Pacific provides stable and reliable results.