Tropospheric Monitoring Over the Ocean using Shipborne GNSS Receiver

An experimental cruise was conducted around the west side of the North Pacific Ocean with a global navigation satellite system (GNSS) antenna, which was installed facing the zenith on the deck of the 3,991-ton research vessel “Hakuho Maru” to investigate the benefits of multi-GNSS processing. More than 100 profiles were also observed by radiosondes released from the ship during the experiment. Using multi-GNSS signals improved the estimation accuracy of coordinates due to the high mean number of satellites. In addition to coordinates, precipitable water vapor (PWV) observed by the GNSS and radiosondes was also compared. The remarkable effect of multi-GNSS processing is demonstrated by the water vapor components. The root means square (rms) and bias of PWV between GPS and radiosonde observations was smaller in the case of multi-GNSS. Although some microwave satellites observe oceanic water vapor, they are insufficient for in-depth study of air–sea interaction. GNSS–PWV is advantageous because of its high accuracy and temporal resolution. More accurate PWV data can be obtained globally over the oceans by this method if GNSS-observing systems are installed in voluntary observing ships or buoys in the future. High-quality PWV data over the ocean would be useful for numerical weather predictions, such as for typhoons or hurricanes.