Determination on precipitable water vapor from ground-based GNSS and COSMIC-2 radio occultation over Taiwan

FORMOSAT-7/COSMIC-2 have launched on June 2019 and provided high space resolution RO profile data. The data can be benefit for weather and climate studies, as well as increasing the accuracy of weather forecast. This study aims to assess two years COSMIC-2 RO-PWV (precipitable water vapor) accuracy. Ten years GNSS-PWV data inverted from PPP (precise point positioning) are better than from DD (double difference) method when taking radiosonde observed data as reference true value in Taiwan. Hence in this study GNSS-PWV from PPP are compared with the COSMIC-2 RO-PWV to verify the accuracy of RO-PWV. RO-PWV derived from COSMIC-2 in 2020 and 2021 is underestimated when taking GNSS-PWV as reference. Removing the elevation of the lowest point of an RO event above 5km can avoid the RO event with error exceed 40mm, and obtain mean RO error of 6.8mm.