Validation of the multi-satellite merged sea surface salinity in the South China Sea

Sea surface salinity (SSS) is an essential variable of ocean dynamics and climate research. The Soil Moisture and Ocean Salinity (SMOS), Aquarius, and Soil Moisture Active Passive (SMAP) satellite missions all provide SSS measurements. The European Space Agency (ESA) Climate Change Initiative Sea Surface Salinity (CCI-SSS) project merged these three satellite SSS data to produce CCI L4 SSS products. We validated the accuracy of the four satellite products (CCI, SMOS, Aquarius, and SMAP) using in-situ gridded data and Argo floats in the South China Sea (SCS). Compared with in-situ gridded data, it shows that the CCI achieved the best performance (RMSD: 0.365) on monthly time scales. The RMSD of SMOS, Aquarius, and SMAP (SMOS: 0.389; Aquarius: 0.409; SMAP: 0.391) are close, and the SMOS takes a slight advantage in contrast with Aquarius and SMAP. Large discrepancies can be found near the coastline and in the shelf seas. Meanwhile, CCI with lower RMSD (0.295) perform better than single satellite data (SMOS: 0.517; SMAP: 0.297) on weekly time scales compared with Argo floats. Overall, the merged CCI have the smallest RMSD among the four satellite products in the SCS on both weekly time scales and monthly time scales, which illustrates the improved accuracy of merged CCI compared with the individual satellite data.