Intercomparison of Multi-Satellite Merged CCI Sea Surface Salinity Product with SMOS, Aquarius, and SMAP

Launching salinity satellites has alleviated the scarcity of sea surface salinity (SSS) data, enabling new methods for monitoring global SSS. The European Space Agency (ESA) integrated multi-satellite data, including the Soil Moisture and Ocean Salinity (SMOS) satellite, the Aquarius satellite, and the Soil Moisture Active-Passive (SMAP) satellite, and released the Climate Change Initiative (CCI) salinity product. The quality assessment of satellite-derived salinity products is a critical prerequisite for ensuring their application reliability. This study evaluated monthly and weekly satellite-derived salinity products, including CCI, Aquarius, SMOS, and SMAP, from the perspectives of data quality and their ability to capture ocean phenomena. Results indicated that the CCI monthly product achieved the highest accuracy, with a bias within 0.1 Practical Salinity Unit (PSU) and Root Mean Square Error (RMSE) around 0.1 PSU in open-ocean regions (60°S–60°N). All products effectively reflected El Niño-Southern Oscillation (ENSO)-related salinity shifts. On a weekly scale, CCI exhibited a stronger correlation with in situ SSS data, with Root Mean Square Error (RMSE) of 0.2–0.3 PSU. CCI effectively captured the weekly-scale variations in SSS, with RMSEs of 0.23 PSU in the Indian Ocean moored buoy array and 0.16 PSU in the Pacific and Atlantic tropical moored buoy arrays. Comparisons with buoy and Array for Real-time Geostrophic Oceanography (Argo) data highlight CCI's potential as a reference for buoy SSS data quality control.