Independent Validation of Total Precipitable Water From Morphed Integrated Microwave Imagery at CIMSS: A Global Study Using GNSS and Radiosonde Measurements

The total precipitable water (TPW) product, obtained from Morphed Integrated Microwave Imagery at Cooperative Institute for Meteorological Satellite Studies (CIMSS) (MIMIC), is generated using multi-satellite microwave (MW) sensors. This product provides high-temporal-resolution and near-real-time TPW over both land and ocean worldwide, which addresses the gap in MW-based TPW products for land areas. However, the accuracy of the MIMIC TPW product has not been validated thoroughly and systematically, hindering a full understanding of its capabilities, limitations, and potential applications in weather and climate research. For the first time, we perform a comprehensive validation of the performance of the MIMIC TPW Version 2 product using reference water vapor observations from Global Navigation Satellite System (GNSS) and radiosonde (RS) stations between 2017 and 2020 across the globe. A total of 16,998,104 MIMIC-GNSS and 858,037 MIMIC-RS data pairs are utilized in our validation procedure. Compared to GNSS data, the MIMIC TPW data exhibits the R2, root-mean-square error (RMSE), relative RMSE, standard deviation, mean absolute percentage error, and mean bias of 0.77, 6.29 mm, 33.99%, 6.29 mm, 40.45%, and 0.06 mm, respectively. Compared to RS data, these values are computed to 0.92, 4.89 mm, 21.79%, 4.83 mm, 20.73%, and -0.75 mm, respectively. The MIMIC TPW product has higher RMSE in large TPW conditions, with limited variations across various advection times. The global TPW distribution is well-aligned between MIMIC and ERA5.