Evaluating the Accuracy of Satellite-Based Microwave Radiometer PWV Products Using Shipborne GNSS Observations Across the Pacific Ocean

Satellite-based conically scanning microwave radiometers are capable of making precipitable water vapor (PWV) observations over the vast ocean regions. In this study, PWV from five on-orbit satellite-based microwave radiometers (SMWRs), i.e., special sensor microwave imager/sounder (SSMIS) F16, SSMIS F17, SSMIS F18, Advanced Microwave Scanning Radiometer 2 (AMSR2), and global precipitation measurement (GPM) microwave imager (GMI), are evaluated by shipborne global navigation satellite system (GNSS) PWV during a 77-day cruise across the Pacific Ocean from June 01, 2017, to August 16, 2017. This cruise crossed about 90° in latitude (from 40° S to 50° N) and about 174° in longitude (from 72° W to 114° E). The shipborne GNSS PWV is first compared with PWV derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) products. The comparison results show that the root mean square error (RMSE) between shipborne GNSS PWV and ERA5 PWV is 2.1 kg/m2. The shipborne GNSS PWV is then used to evaluate the PWV derived from five SMWRs. The statistical results show that the PWV from all SMWR has a good agreement with shipborne GNSS PWV. The PWV RMSEs of SSMIS F16, SSMIS F17, SSMIS F18, AMSR2, and GMI evaluated by shipborne GNSS PWV are 2.0, 2.0, 1.8, 1.5, and 1.7 kg/m2, respectively. In addition, statistical results indicate that SSMIS F16, SSMIS F17, SSMIS F18, AMSR2, and GMI overestimate PWV with respect to GNSS by 1.1, 0.5, 0.5, 0.4, and 0.4 kg/m2, respectively.